NV-center-based microwave-free quantum sensor and uses and characteristics thereof

[0001] The present patent application is a divisional of, and claims priority to, U.S. application Ser. No. 17/629,171, filed on Jan. 21, 2022, which is a national stage of, and claims priority to, Patent Cooperation Treaty Application No. PCT/DE2020/100648, filed on Jul. 22, 2020, which application claims the priority of the German patent applications DE 10 2019 009 153.1 filed on Jul. 25, 2019, DE 10 2019 009 155.8 filed on Aug. 5, 2019, DE 10 2019 005 484.9 filed on Aug. 5, 2019, DE 10 2019 129 092.9 filed on Oct. 28, 2019, DE 10 2019 130 115.7 filed on Nov. 7, 2019, DE 10 2020 107 831.5 filed on Mar. 22, 2020, and DE 10 2020 003 532.9 filed on Apr. 5, 2020, the disclosures of which are incorporated by reference in the present patent application.

[0002] The disclosure relates, inter alia, to a method and a device for generating acoustically equivalent electrical and digital signals by means of sensors based on quantum mechanical effects as microphones or pickups for musical instruments and other technical and medical instruments. The present disclosure thus relates in particular to the detection of magnetic flux densities B, electric flux densities D, pressures P, motion velocities v, position coordinates, distances, electric currents, forces on atomic nuclei afflicted with a magnetic moment, accelerations a, gravitational field strengths g, mechanical and electromagnetic oscillations, rotational velocities ω, temperatures ϑ, intensities of ionizing radiations by means of sensors based on quantum mechanical effects. The mechanical vibrations can be used, for example, in musical instruments to produce tones. The evaluation of amplitude and frequency of mechanical vibrations can also be used for quality control of motors or other regularly moving components. Further applications are the use as seismograph or for medical examinations.

[0003] Generic methods to convert positions, movements, accelerations, rotational speeds, or vibrations into electrically or digitally equivalent signals are pressure-based sensors, thermoelastic or magnetic induction-based methods. The latter is particularly common for electric (electric) guitars and basses. According to the prior art, it is known, for example, that electric guitars or electric basses are equipped with pick-ups in order to convert the vibrations of a struck string into acoustic signals. This uses the induction of voltages by means of temporal field changes in a coil according to Faraday's law. The determination of vibrations by geophones also uses a coupling of earth vibrations to a coil in which a free-moving magnet is located.

[0004] A fundamental disadvantage of these methods is that the induction voltage is determined by the temporal change of the magnetic field, in particular by the change of the magnetic flux B, thus representing a differential filter with a corresponding noise amplification. Likewise, the induction of the coil in the measuring system represents a low-pass filter and leads to non-linear transmissions of mechanically composed oscillations of different frequencies. Pressure-based sensors have similar disadvantages. Conventional magnetic sensors also have the disadvantage of low sensitivity or strong temperature dependence, or both. For example, Hall sensor elements have a high internal resistance, which limits the measurement speed. Consequently, the transfer of mechanical vibrations into acoustically equivalent electrical or digital signals is only possible to a limited extent with the present technology. The disclosure is further directed to a housing comprising a sensor system and/or quantum technological system. The sensor system comprises a sensor element having a paramagnetic center (NV1) in the material of a sensor element. All sub-devices of the sensor system are preferably non-ferromagnetic. This relates in particular to the lead frame for mounting the sensor system within an open cavity housing. The paramagnetic center (NV1) is preferably an NV center in a diamond crystal serving as the sensing element, in which case diamond is at least in part the sensing element material. The use of other centers, such as the ST1 center or the SiV center or the GeV center is conceivable. The disclosure is also directed to a corresponding sensor system and/or quantum technological system, wherein the optical transmitter (PL1) of the sensor system is chopped, i.e., pulse modulated. By a special measure, all residues of the chopper frequency spectrum are removed from the spectrum of the sensor output signal (out). In particular, a special type of noise reduction is claimed. As used herein, pulse modulation refers to various modulation techniques such as pulse amplitude modulation (PAM), pulse code modulation (PCM), pulse frequency modulation (PFM), pulse width modulation (PWM), pulse pause modulation (PPM), pulse phase modulation (PPM), and pulse position modulation (PPM). Reference is made to hyperlink https://de.wikipedia.org/wiki/Pulsmodulation.

[0005] The features described in the following and the features of the claims can typically be combined with each other, even if such combinations are not combined with each other in the claims of the first application, since in part due to lack of space only preferred and/or exemplary combinations were reflected in the claims and the description. The prerequisite for such a combination, which may not be expressly described herein, is that the combination is useful and functional and can be tested by the skilled person, if necessary. The disclosure expressly includes such combinations.

[0006] Recently, many publications have been made on the use of NV centers as quantum dots for quantum sensing, quantum computing and quantum cryptography.

[0007] Sensors based on quantum mechanical effects are preferably based on paramagnetic spin states and generate no or an extremely low magnetic field themselves. They allow magnetic fields of up to several hundred kHz to be determined independently of frequency. Compared to magnetic field measurement methods based on induction, the measurement system does not affect the oscillating system to be measured and thus allows an uninfluenced measurement of the system to be measured. Due to the measurement principle based on quantum mechanical effects, the detection principle is largely insensitive to temperature.

[0008] FIG. 1 shows a prior art quantum dot-based measurement system schematically as a highly simplified block diagram. In the prior art, a pump radiation source (PL1) with a pump radiation wavelength (λ_pmp) emits pump radiation (LB) into a first transmission path (I1) as a function of a transmission signal (S5). For the intensity i1 of the pump radiation (LB) emitted into the first transmission path (I1), we find the equation I in linear approximation:

[0009] $I1=h0+\mathrm{hRa}+h1*\left(s5w+s5g+\mathrm{hRb}\right)$

[0010] Here h0 describes an offset value that is specific to the pump radiation source (PL1). hRa describes a noise that is independent of intensity. h1 describes a proportionality factor that applies to the pump radiation source (PL1) at the selected operating point with a linear approximation. s5w represents the instantaneous value of the alternating component (S5w) of the transmission signal (S5). s5g represents the instantaneous value of the DC component (S5g) of the transmission signal (S5). hRb represents the co-amplified input noise of the pump radiation source (PL1). Thus, in the prior art, the pump radiation source (PL1) is modulated with the transmission signal (S5).

[0011] Only a first portion a1 of the pump radiation (LB), which is located in the first transmission path (I1), reaches the sensor element with the paramagnetic center (NV1) or the paramagnetic centers (NV1). Preferably, the sensor element is one or more diamonds and the paramagnetic center (NV1) in this case is then preferably one or more NV centers.

[0012] The pump radiation (LB) from the first transmission path (I1) thus irradiates the paramagnetic center or centers (NV1) of the sensor element with pump radiation (LB). The paramagnetic center or centers (NV1) convert a second portion a2 of the received pump radiation (LB) into a fluorescence radiation (FL) having an intensity i2.

[0013] $i2=a1*a2*\left[h0+\mathrm{hRa}+h1*\left(s5w+s5g+\mathrm{hRb}\right)\right]$

[0014] The paramagnetic center (NV1) or centers (NV1) thus radiate the fluorescence radiation (FL) into a second transmission path (I2) with intensity i2. The sensor element also reflects or transmits a third portion a3 of the pump radiation (LB) into the second transmission path (I2).

[0015] $i2=a1*a2*\left[h0+\mathrm{hRa}+h1*\left(s5w+s5g+\mathrm{hRb}\right)\right]+a1*a3*\left[h0+\mathrm{hRa}+h1*\left(s5w+s5g+\mathrm{hRb}\right)\right]$

[0016] An optical filter (F1), which is assumed to be ideal here, transmits the fluorescence radiation (FL) and absorbs or reflects the pump radiation (LB) so that only a fourth fraction a4 of the fluorescence radiation (FL) reaches the radiation receiver (PD).

[0017] $i{2}^{\prime }=a4*a1*a2*\left[h0+\mathrm{hRa}+h1*\left(s5w+s5g+\mathrm{hRb}\right)\right]$

[0018] At the end of the second transmission path (I2), the radiation receiver (PD) receives this portion of the fluorescence radiation (FL) with intensity i2′ and converts it into a receiver output signal (S0) with value (s0).

[0019] $s0=d0+\mathrm{dRa}+d1*\left(I{2}^{\prime }+\mathrm{dRb}\right)$ $s0=d0+\mathrm{dRa}+d1*\left(a4*a1*a2*\left[h0+\mathrm{hRa}+h1*\left(s5w+s5g+\mathrm{hRb}\right)\right]+\mathrm{dRb}\right)$

[0020] Here, d0 describes an offset value specific to the radiation receiver (PD). dRa describes a noise of the radiation receiver (PD) that is independent of the intensity. d1 describes a proportionality factor that applies to the radiation receiver (PD) at the selected operating point with linear approximation. dRb stands for the co-amplified input noise of the radiation receiver (PD). Multiplying out results in:

[0021] $s0=d0+\mathrm{dRa}+d1*a4*a1*a2*h0+d1*a4*a1*a2*\mathrm{hRa}+d1*a4*a1*a2*h1*s5w+d1*a4*a1*a2*h1*s5g+d1*a4*a1*a2*h1*\mathrm{hRb}+d1*a4*a1*a2*\mathrm{dRb}$

[0022] In the prior art, multiplication is then performed with the instantaneous value (s5w) of the alternating component (S5w) of the transmission signal (S5) to the filter input signal (S3):

[0023] $s3=d0*s5w+\mathrm{dRa}*s5w+d1*a4*a1*a2*h0*s5w+d1*a4*a1*a2*\mathrm{hRa}*s5w+d1*a4*a1*a2*h1*s5w*s5w+d1*a4*a1*a2*h1*s5g*s5w+d1*a4*a1*a2*h1*\mathrm{hRb}*s5w+d1*a4*a1*a2*\mathrm{dRb}*s5w$

[0024] We now use a linear loop filter (TP) with the filter function F[X1]. Let X1 and X1 be the two values of any two signals. Let x be any real factor. For the purposes of this disclosure, a filter with filter function F[X1] is a linear filter if (Equation XIII) holds:

[0025] $F\left[X1+X2\right]=F\left[X1\right]+F\left[X2\right]$ $F\left[x*X1\right]=x*F\left[X1\right]$

[0026] This filter input signal (S3) is then filtered in a low-pass filter as a loop filter (TP) in the prior art.

[0027] This loop filter (TP) is a linear filter with filter function F[s3] according to Equation XIII, thus the value (s3) of the filter input signal (S3) is to be the input variable of the filter function F[ ].

[0028] The structure of the loop filter (TP) is typically chosen so that at least approximately:

[0029] $F\left[s5w\right]=0$ $F\left[s5w*s5w\right]=1$ $F\left[1\right]=1$

[0030] For the filter output signal (S4) we then obtain:

[0031] $s4=d0*F\left[s5w\right]+F\left[\mathrm{dRa}*s5w\right]+d1*a4*a1*a2*h0*F\left[s5w\right]+d1*a4*a1*a2*F\left[\mathrm{hRa}*s5w\right]+d1*a4*a1*a2*h1*F\left[s5w*s5w\right]+d1*a4*a1*a2*h1*s5g*F\left[s5w\right]+d1*a4*a1*a2*h1*F\left[\mathrm{hRb}*s5w\right]+d1*a4*a1*a2*F\left[\mathrm{dRb}*s5w\right]$

[0032] With F[s5w]=0 and F[s5w*s5f]=1 we then find:

[0033] $s4=d1*a4*a1*a2*h1+F\left[\mathrm{dRa}*s5w\right]+d1*a4*a1*a2*F\left[\mathrm{hRa}*s5w\right]+d1*a4*a1*a2*h1*F\left[h\mathrm{Rb}*s5w\right]+d1*a4*a1*a2*F\left[\mathrm{dRb}*s5w\right]$

[0034] As can be easily seen, the noise is reduced by mixing higher-frequency noise components down with the transmission signal (S5). Since the noise levels of these noise components are smaller with respect to 1/f smoking, which is dominant at low frequencies, there is an improvement in the noise performance. However, the noise, especially the white noise, does not disappear.

[0035] The instantaneous value (s0) of the receiver output signal (S0) is multiplied by the instantaneous value (s5) of the transmission signal (S5) and the resulting value of the filter input signal is then filtered in a loop filter (TP).

[0036] This problem is significantly reduced by the apparatus and method disclosed herein. Complete elimination of noise is not known to be possible for physical reasons.

[0037] Furthermore, there are no known methods in the prior art for producing diamonds with a high density of NV centers, which are necessary to obtain a good measurement signal.

[0038] Moreover, no methods for enhancing contrast (KT) are known in the prior art.

[0039] The healing of crystal damage and the change in appearance of diamonds is already known from U.S. Pat. No. 4,124,690 A, without disclosing the production of red diamonds.

[0040] A process for reducing the colour of diamonds is known from EP 0 014 528 B1. This is a process for reducing the colour of type 1b diamonds, which according to EP 0 014 528 B1 is characterised by the fact that the diamond is subjected to irradiation with such an energy current and that at least 1018 lattice gaps per cm³ are produced in the diamond. According to the technical teaching of EP 0 014 528 B1, the irradiated diamond is then heat treated at a temperature of 1600° C. to 2200° C. under a pressure at which the diamond is crystallographically stable at the applied temperature.

[0041] From EP 0 275 063 A2 a method for generating a high NV center density in diamond is known, in which the diamond is irradiated with electrons of high energy and then annealed at a temperature between 500° C. and a pressure lower than 1 Torr.

[0042] A method for producing a red diamond is known from EP 0 615 954 A1. The method of EP 0 615 954 A1 comprises the steps:

• • [0043] 1. Preparation of a synthetic diamond crystal containing at least 1×10¹⁷ and less than 4×10¹⁸ atoms/cm³ of type Ib nitrogen and less than 1×10¹⁸ atoms/cm³ of boron;
  • [0044] 2. irradiating the diamond crystal with an electron beam at an energy of 1 to 10 MeV in a density range of 2×10¹⁵ to 5×10¹⁶ electrons/cm² or with a neutron beam in a density range of 2×10¹⁵ to 8×10¹⁷/cm² and
  • [0045] 3. Annealing the diamond crystal irradiated with the electron beam or the neutron beam in a vacuum atmosphere or an inert gas atmosphere of not more than 10⁻¹ Torr at a temperature of at least 600° C. and less than 800° C. for at least 3 hours.

[0046] Irradiation with the electron beam or neutron beam causes radiation damage in the diamond, which cannot be removed even with subsequent annealing. Therefore, diamonds treated in this way are typically slightly cloudy.

[0047] According to the technical teachings of EP 0 615 954 A1, a red diamond thus produced has an absorption coefficient for type Ib nitrogen at 500 nm wavelength of at least 0.1 cm⁻¹ and less than 0.2 cm⁻¹ and an NV center-caused absorption coefficient at 570 nm which is at least 0m05 cm⁻¹ and less than 1 cm⁻¹. The absorption coefficient of the GR1 center, the H2 center, the H3 center and the H4 center in the visible region are typically less than 0.2 cm⁻¹ in a red diamond fabricated according to the technical teachings of EP 0 615 954 A1.

[0048] From RU 2 145 365 C1 a process is known for refining diamonds by exposing them to electron beams and annealing them for a period of time ranging from 30 minutes to several hours before the diamonds acquire specific shades of color. According to RU 2 145 365 C1, the process of RU 2 145 365 C1 is characterized in that the diamonds are subjected to a treatment with electron beams with an integrated electron flow in the range of 5×10¹⁵-5×10¹⁸ cm⁻² and in that the annealing is carried out either at atmospheric pressure or at atmospheric pressure or in vacuum or in an atmosphere of inert gases at 300-1900° C. Also, in the technical teaching of RU 2 145 365 C1, the irradiation-annealing sequence is preferably repeated several times in order to prevent agglomeration of radiation damage into agglomerations which can no longer be dissolved.

[0049] From EP 0 316 856 B1, purple diamonds are known having absorption coefficients of 0.2-2 cm⁻¹ of Ib type nitrogen at 500 nm and of 0.3-10 cm⁻¹ of NV center at 570 nm, said diamonds having an absorption coefficient of less than 0.2 cm⁻¹ of GR1, H2, H3 and H4 centers in the visible region. In the method according to the technical teachings of EP 0 316 856 B1 for producing purple diamonds, an artificial synthetic diamond crystal of Ib type having an Ib nitrogen content of the crystal in the range of 8×10¹⁷ to 1.4×10¹⁹ atoms/cm³ is used, the crystal being subjected to electron irradiation of 5×10¹⁶-2×10¹⁸ electrons/cm² at 2-4 MeV and an annealing process at a temperature of 800-1100° C. According to the technical teachings of EP 0 316 856 B1, the process is characterized by the fact that the annealing process is carried out in a vacuum of less than 1.33 Pa (10⁻² Torr) for more than 25 hours, i.e., for a very long time. It is also known from EP 0 316 856 B1 that, if necessary, further irradiations with electrons and further annealing steps can follow after annealing by means of an annealing step.

[0050] A method for forming color centers in diamond is known from RU 2015 132 335 A. The method of RU 2015 132 335 A comprises irradiating the diamonds. According to the technical teachings of RU 2015 132 335 A, the diamonds should have a uniform volume distribution of A aggregates with a concentration of at least 10¹⁸ cm.⁻³ According to the RU 2015 132 335 A, the ionizing radiation used for irradiation should have an energy of at least 1 MeV at a dose of 100-120 ppm/cm² per A unit. According to RU 2015 132 335 A, the technical teaching of RU 2015 132 335 A is characterized in that the irradiation is carried out with an intermediate annealing at a temperature of 850-900 K repeatedly until the desired concentration of color centers is reached, followed by an annealing of the diamond in an inert medium at a temperature of 1200-2000 K for 0.5-2 hours. The intermediate annealing already improves the healing of the radiation damage, but cannot prevent the damage from agglomerating and the diamond from becoming cloudy.

[0051] From EP 1 645 664 A1, a process for the production of fancy red diamonds with stable coloring centers that absorb in the range of wavelengths from 400 to 640 nm is known. The process of EP 1 645 664 A1 is based on irradiating the diamonds with an electron current and hardening at a temperature of at least 1100° C. in a vacuum. According to EP 1 645 664 A1, the process of EP 1 645 664 A1 is characterized by the fact that natural diamonds of type 1a are used and that in the crystal lattice of these natural diamonds isolated nitrogen atoms are formed in the substitutional position of depletion type C. The process of EP 1 645 664 A1 is based on the irradiation of diamonds with an electron current and hardening at a temperature of at least 1100° C. in a vacuum. This happens according to the technical teaching of EP 1 645 664 A1 by a high-temperature processing in a high-pressure apparatus at a temperature higher than 2150° C. and at a stabilized pressure of 6.0-7.0 Gpa, which is carried out before irradiation by a high-energy electron current with a dose of 5×10¹⁵-5×10¹⁸ cm⁻² at 2-4 MV, using diamonds containing depletion type A, or by a high-energy electron current with a dose of more than 10¹⁹ cm⁻² using natural diamonds with a high nitrogen content containing more than 800 ppm nitrogen admixture as depletion type A and B1 nitrogen admixture as depletion type A and B1.

[0052] U.S. Pat. No. 8,986,646 B2 discloses a method for generating NV centers in CVD diamond material. According to the technical teaching of U.S. Pat. No. 8,986,646 B2, the method of U.S. Pat. No. 8,986,646 B2 comprises irradiating the diamond material and then annealing the diamond material. According to the technical teaching of U.S. Pat. No. 8,986,646 B2, the diamond material that is irradiated is single crystal diamond material grown by a CVD process and containing single substitution nitrogen atoms (N_sO). The diamond material according to U.S. Pat. No. 8,986,646 B2 has an absorption spectrum with an integrated total absorption in the visible range from 350 nm to 750 nm, in which at least 10% of the integrated absorption is due to absorption by N_sO. Irradiation is performed to produce isolated vacancies V in the CVD diamond material. According to U.S. Pat. No. 8,986,646 B2, the concentration of the isolated vacancies in the irradiated diamond material after irradiation is at least 0.05 ppm and at most 1 ppm, both to provide sufficient vacancies for the formation of the NV centers and to avoid agglomeration of the vacancies into larger complexes. The technical teaching of U.S. Pat. No. 8,986,646 B2 provides for subsequent annealing of the irradiated diamond material to form NV centers from at least some of the individual substitutional nitrogen defects (N_sO) and the introduced isolated vacancies. According to the technical teachings of U.S. Pat. No. 8,986,646 B2, the treated CVD diamond material after the irradiation and annealing steps (i) and (ii) has the following properties: [V⁰ GR1<0.3 ppm, [V] ND1<0.3 ppm, [N_sO]<1.5 ppm, [V chains]<20 cm⁻¹ at 250 nm, [NV]≥10¹² cm⁻³. The technical teachings of U.S. Pat. No. 8,986,646 B2 provide for an annealing temperature of 1600° C.

[0053] U.S. Pat. No. 8,961,920 B1 discloses a method for changing the color of a diamond. The method of U.S. Pat. No. 8,961,920 B1 starts with identifying a nitrogen content of a type IaB diamond, the diamond initially having a first color. This is followed, according to the technical teachings of U.S. Pat. No. 8,961,920 B1, by processing the diamond in a high pressure/high temperature (“HPHT”) press under diamond stable conditions to change the color of the diamond from the first color to a second color comprising yellow. Then, according to the technical teaching of U.S. Pat. No. 8,961,920 B1, irradiating the diamond with electrons having an energy between about 1 MeV and about 20 MeV is performed to change the color of the diamond from the second color to a third color, which is bluish-greenish. Finally, in accordance with the technical teachings of U.S. Pat. No. 8,961,920 B1, annealing of the diamond is then performed at a temperature of less than 1100° C. and under vacuum or a pressure of not more than about 500 kPa to change the color of the diamond from the third color to a fourth color which is red, pink, or purple. Irradiation with the electron beam causes radiation damage to the diamond, which cannot be removed even with subsequent annealing. Therefore, diamonds treated in this way are typically slightly cloudy.

[0054] U.S. Pat. No. 8,168,413 B2 discloses a process for producing luminescent diamond particles, which comprise irradiating diamond particles with an ion beam. According to the technical teachings of U.S. Pat. No. 8,168,413 B2 the diamond particles have a diameter of 1 nm to 1 mm and 5 ppm to 1000 ppm color centers. According to the technical teachings of U.S. Pat. No. 8,168,413 B2, the ion beam has a kinetic energy of 1 keV to 900 MeV. According to the technical teaching of U.S. Pat. No. 8,168,413 B2, the irradiation is followed by heating the irradiated diamond particles in a non-oxidizing atmosphere to a temperature between 600 and 1000° C. and oxidizing the surface of the luminescent diamond particles. The irradiation with the electron beam causes radiation damage in the diamond, which cannot be removed even with subsequent annealing. Therefore, diamonds treated in this way are typically slightly cloudy.

[0055] A method of changing the color of a diamond is known from EP 1 097 107 B1. According to the technical teaching of EP 1 097 107 B1, the method comprises subjecting the diamond to irradiation with an energy suitable to cause photonuclear transmutation of selected atoms to other atoms. According to the technical teachings of EP 1 097 107 B1, this energy is selected to excite a giant dipole resonance (GDR) in the diamond. According to the technical teaching of EP 1 097 107 B1, the irradiation is such that either: (1) transmutations of carbon atoms to boron atoms are caused, imparting a blue color to the diamond, or (2) in the case of a nitrogenous yellow diamond, that transmutations of nitrogen atoms to carbon atoms are caused, reducing the yellow color of the diamond. Further, according to the technical teachings of EP 1 097 107 B1, the method of EP 1 097 107 B1 comprises reducing radiation damage in the diamond by cooling the diamond to restore the diamond crystal lattice, the color change due to the transmutation according to EP 1 097 107 B1 being unaffected. A red color was not reported here in EP 1 097 107 B1.

[0056] JPH 0 536 399 B2 describes a process for the blue coloring of diamonds by means of an electron beam and water-cooling during irradiation.

[0057] From U.S. Pat. No. 5,637,878 A, a method for coloring jewelry diamonds is known in which the jewelry diamond blanks are irradiated with an electron beam. The method of U.S. Pat. No. 5,637,878 A for electron beam irradiation of gemstones for color enhancement comprises the steps:

• • [0058] 1. Placing the gemstones in a vibratory medium that has been provided with a coolant;
  • [0059] 2. Circulating a coolant through the coolant device;
  • [0060] 3. Initiating an oscillating motion along a horizontal y-axis in the oscillating means;
  • [0061] 4. Aiming an oscillating electron beam generated by an electron beam source having a power of about 10 kW to about 500 kW at the gemstones, wherein the oscillating electron beam travels along a z-axis;
  • [0062] 5. Maintaining coolant circulation through the coolant until the gems have cooled to ambient temperature; and
  • [0063] 6. Removing the evenly colored gemstones.

[0064] The technical teachings of U.S. Pat. No. 5,637,878 A further disclose a preferred electron energy of 3 MeV to 5 MeV.

[0065] A diamond modification method is known from CN 107 840 331 A, which according to CN 107 840 331 A is characterized in that the method of CN 107 840 331 A comprises treating the diamond with a radiation beam comprising protons, wherein the energy difference between the highest energy and the lowest energy of the protons comprises at least 5 MeV. According to the technical teaching of CN 107 840 331 A, the radiation source used is cosmic radiation at an altitude of at least 20 km.

[0066] From US 2009 0 110 626 A1 an annealing process is known, in which the diamond is very quickly brought to a high temperature of approx. 2200° C. under high pressure.

[0067] From U.S. Pat. No. 7,604,846 B2 a recoloring of diamonds by means of ion bombardment and subsequent annealing is known, which exhibits the problems of the prior art already discussed.

[0068] The processes for the artificial production of red diamonds have in common that, as a rule, an irradiation with ionizing radiation takes place and then, in a subsequent step, an attempt is made to repair the radiation damage in the diamond blank by means of a heat treatment, which may also take place under high pressure. This procedure has the massive disadvantage that flaws form in the diamond crystal during the high-energy irradiation. These tend to cluster together to form larger complexes, which can then no longer be dissolved with the subsequent heat treatment.

[0069] It is true that, as described above, attempts have been made to prevent this agglomeration of the defects into larger complexes by cyclic repeated irradiation and subsequent healing. However, this can only be done with partial success.

[0070] These clusters of flaws lead to a clouding of the jewelry diamonds and thus to a deficiency with regard to the so-called “clarity” of the jewelry diamonds. Such stones are called “cloudy” and their value is diminished due to the reduced optical brilliance. From the paper M. Capelli, A. H. Heffernan, T. Ohshima, H. Abe, J. Jeske, A. Hope, A. D. Greentree, P. Reineck, B. C. Gibson, Increased nitrogen-vacancy center creation yield in diamond through electron beam irradiation at high temperature, Carbon (2018), doi: https://doi.org/10.1016/j.carbon.2018.11.051, an increase in NV center yield is known but not yet sufficient.

[0071] From CAPELLI, Marco, et al. “Increased nitrogen-vacancy center creation yield in diamond through electron beam irradiation at high temperature”, Carbon, 2019, 143. yr., pp. 714-719 a procedure for insitu healing of radiation damage of an electron irradiation with 2 MeV electrons at high temperature is known. FIG. 6 of Capelli's paper shows a maximum final NV center concentration of 50 ppm*(maximum) 4% conversion rate 2 ppm for an initial nitrogen concentration 50 ppm. The maximum conversion rate according to FIG. 6 of Capelli's writing is 4% at about 0.8 ppm NV content. For 200 ppm initial nitrogen content, FIG. 6 of Capelli's writing discloses a conversion rate of 0.5%, corresponding to about 1 ppm NV center density. Thus, Capelli's writing does not disclose a concentration>2%. Even with the assumption of 4% conversion rate for 200 ppm not supported by Capelli's writing, no concentration>8 ppm can be inferred from the technical teachings of Capelli's writing.

[0072] Microwave-free magnetometry with nitrogen-vacancy centers in diamond is known from ARNE WICKENBROCK ET AL, “Microwave-free magnetometry with nitrogen-vacancy centers in diamond,” ARXIV.org, CORNELL UNIVERSITY LIBRARY, 201 OLIN LIBRARY CORNELL UNIVERSITY ITHACA, NY 14853, Jun. 9, 2016 (2016-06-09), XP080965843, DOI: 10.1063/1.4960171. The paper by Wickenbrock gives <200 ppm as the initial concentration of nitrogen atoms in diamond before electron irradiation. With a conversion degree of 0.5% based on the value for an initial NV center density of 200 ppm from FIG. 6 of Capelli's writing, this gives a maximum concentration of NV center concentration in the diamond of Wickenbrock's writing of 1 ppm. The best conversion rate of Capelli's writing is 4% with an initial nitrogen content of 25 ppm. Even if this much too optimistic conversion rate of 4%, based on the value for an initial NV center density of 25 ppm from FIG. 6 of Capelli's paper, were also effective at 200 ppm—which it is not—it would still result in a maximum concentration of 8 ppm, the production of which, however, is no longer covered by the prior art. According to FIG. 6 of Capelli's paper, however, only a concentration of NV centers in the diamond of <3 ppm can be expected under these conditions.

[0073] From WO 2019 108 781 A1 a stationary solid state spin sensor with magnetic angle is known. WO 2019 108 781 A1 leaves open how the NV centers are generated. In section WO 2019 108 781 A1, the authors of WO 2019 108 781 A1 write, “Because the magic-angle-spinning magnetic field mitigates dipolar coupling between the color center defects and unwanted paramagnetic impurities that create small magnetic fields localized around each color center defect, the solid-state host 1310 can be doped at a higher doping density than in conventional solid-state spin sensors. For example, the density of the color center defects in the solid-state host 1310 may range from about 1.76 c 10¹⁴ cm⁻³ to about 1.76 c 10¹⁹ cm⁻³ (1 ppb to 100 ppm). This higher doping density enables more sensitive measurements and finer spatial resolution for imaging magnetic fields and other physical quantities.” Unfortunately, however, WO 2019 108 781 A1 leaves completely open how such diamonds can be produced or where they can be obtained.

[0074] US 2015 0 090 033 A1 discloses a gyroscope based on nitrogen defect centers in diamond. US 2015 0 090 033 A1 writes in its section “The NV-center concentration after this process is estimated to be on the order of 10 ppm”. I.e., the technical teaching of the US 2015 0 090 033 A1 explains thus that thus the process presented there typically a NV-center-density of 10 ppm can be reached, but just not more. Quite correctly, US 2015 0 090 033 A1 states in the following section: “Diamonds with NV center vacancy concentrations of between approximately 10 ppm and approximately 200 ppm are preferred”. The same applies to section “The preferred number of vacancy centers in the diamond lattice is between approximately 10 ppm and 200 ppm.” It is undoubtedly desirable to achieve the highest possible NV center concentration. However, the technical teaching of US 2015 0 090 033 A1 precisely leaves completely open how to achieve a NV center density of more than 10 ppm in the diamond. Therefore, the technical teaching US 2015 0 090 033 A1 only discloses a method for producing NV centers with a typical NV center density of 10 ppm and unfortunately does not disclose a method for producing NV centers with a typical NV center density of more than 10 ppm. Thus, with respect to NV center concentration>10 ppm, it can only be reworked if NV diamonds from other sources are used. US 2015 0 090 033 A1 does not disclose such a source of diamonds with NV center densities greater than 10 ppm or a method of producing them.

[0075] US 2017 0 328 956 A1 discloses a wireless network-based battery management system.

[0076] None of the writings disclose a method of fabricating diamonds with a concentration of nitrogen void centers (NV centers) with a density greater than 10 ppm let alone 20 ppm.

[0077] Thus, there is a desire in the art to produce high NV center concentrations without a pathway for achieving NV center concentrations>10 ppm being disclosed. There is a significant lack of relevant literature.

[0078] From the paper Gurudev Dutt, Liang Jiang, Jeronimo R. Maze, A. S. Zibrov “Quantum Register Based on Individual Electronic and Nuclear Spin Qubits in Diamond”, Science, Vol. 316, 1312-1316, 01.06.2007, DOI: 10.1126/science.1139831 a method for coupling the nuclear spin of C¹³ nuclei with the electron spins of the electron configuration of NV centers is known.

[0079] From the paper Thiago P. Mayer Alegre, Antonio C. Torrezan de Souza, Gilberto Medeiros-Ribeiro, “Microstrip resonator for microwaves with controllable polarization”, arXiv:0708.0777v2 [cond-mat.other] 11.10.2007 a cross-shaped electrically conductive microwave resonator is known. In this regard, reference is made to their FIG. 2. One application of the cross-shaped microwave resonator named by the authors in the first section of the paper is the driving of paramagnetic centers by means of optically detected magnetic resonance (OMDR). A dedicated named application is quantum information processing (QIP). The substrate of the electrically conductive microwave resonator is a PCB (=printed circuit board). The dimensions of the resonator are 5.5 cm, which is in the order of magnitude of the wavelength of the microwave radiation to be coupled in. The microwave resonator is powered by voltage control. The two beams of the resonator cross are electrically connected. Selective driving of individual paramagnetic centers (NV1) while not driving other paramagnetic centers (NV1) is not possible with the technical teachings of the paper Thiago P. Mayer Alegre, Antonio C. Torrezan de Souza, Gilberto Medeiros-Ribeiro, “Microstrip resonator for microwaves with controllable polarization”, arXiv:0708.0777v2 [cond-mat.other] 11.10.2007.

[0080] From the paper Benjamin Smeltzer, Jean Mcintyre, Lilian Childress “Robust control of individual nuclear spins in diamond”, Phys. Rev. A 80, 050302 (R)-25 Nov. 2009 a method for accessing individual nuclear ¹³C-spins using NV cents in diamond is known.

[0081] From the paper Petr Siyushev, Milos Nesladek, Emilie Bourgeois, Michal Gulka, Jaroslav Hruby, Takashi Yamamoto, Michael Trupke, Tokuyuki Teraji, Junichi Isoya, Fedor Jelezko, “Photoelectrical imaging and coherent spin-state readout of single nitrogen-vacancy centers in diamond” Science 15 Feb. 2019, Vol. 363, Issuc 6428, pp. 728-731, DOI: 10.1126/science.aav2789 electronic readout of spin states of NV centers is known.

[0082] From the paper Timothy J. Proctor, Erika Andersson, Viv Kendon “Universal quantum computation by the unitary control of ancilla qubits and using a fixed ancilla-register interaction”, Phys. Rev. A 88, 042330-24 Oct. 2013 a method for using so-called ancilla quantum bits to entangle a first nuclear spin with a second nuclear spin using ancilla bits is known.

[0083] WO 2016 083 140 A1 discloses a method for measuring the magnetic field with a ramp method and with control of the quantum bit by means of a microwave. From U.S. Pat. No. 9,910,105 B2, the measurement of magnetic fields with Zeeman splitting and microwave driving is known. Also known from U.S. Pat. No. 9,541,610 B2 is a magnetic field sensor using microwaves for quantum dot control. From U.S. Pat. No. 9,551,763 B1 a magnetic field sensor with a 4-sided antenna is known, which also uses microwaves. From U.S. Pat. No. 10,408,889 B2, a controller for a magnetic field sensor for controlling microwaves is known. Also known from U.S. Pat. No. 10,120,039B2 is a magnetic field sensor with microwave control. From U.S. Pat. No. 10,168,393 B2 a magnetic field sensor with microwave control with the aid of a bias magnet is known. Also known from U.S. Pat. No. 10,241,158 B2 is a magnetic field sensor with microwave control. From U.S. Pat. No. 10,345,396 B2, U.S. Pat. No. 10,359,479 B2, U.S. Pat. No. 8,547,090 B2, U.S. Pat. No. 9,557,391 B2, U.S. Pat. No. 9,829,545 B2, U.S. Pat. No. 9,910,104 B2 and U.S. Pat. No. 10,408,890 B2 magnetic field sensors with radio wave drive are known. From U.S. Pat. No. 9,222,887 B2, a magnetic field sensor with nanoparticles and a microwave drive is known. Also known from U.S. Pat. No. 9,632,045 B2 and U.S. Pat. No. 9,658,301 B2 are magnetic field sensors with microwave drive. From U.S. Pat. No. 9,664,767 B2, a method for manipulating NV center spins with Walsh reconstruction based on microwave actuation is known. From U.S. Pat. No. 10,007,885 B1 a measurement using entanglement and pertubation pulses is known. From WO 2018 169 997 A1 a magnetic field measurement using an AFM tip is known.

[0084] U.S. Pat. No. 10,006,973 B2 discloses a magnetic field sensor comprising two photodetectors. According to its technical teachings, the device of U.S. Pat. No. 10,006,973 B2 includes a diamond assembly having a diamond with one or more nitrogen vacancies, a light emitting diode configured to emit light toward the diamond, a first photosensor configured to detect a first portion of the light emitted from the light emitting diode, a second photosensor configured to detect a second portion of the light emitted from the light emitting diode, and a processor operatively coupled to the first photosensor and a second photosensor. The first portion of the light does not travel through the diamond according to the technical teachings of U.S. Pat. No. 10,006,973 B2, whereas the second portion of the light does travel through the diamond according to the technical teachings of U.S. Pat. No. 10,006,973 B2. In U.S. Pat. No. 10,006,973 B2, the processor is configured to compare a first signal received from the first photosensor with a second signal received from the second photosensor and to determine, based on the comparison of the first signal and the second signal, the strength of a magnetic field applied to the diamond. Similar constructions are known from U.S. Pat. No. 9,720,055 B1, U.S. Pat. No. 9,817,081 B2, and U.S. Pat. No. 9,823,314 B2, which use three optical sensors.

[0085] U.S. Pat. No. 10,012,704 B2 discloses a magnetic field sensing device using a resistive inductive conductor loop. The technical teachings of U.S. Pat. No. 10,012,704 B2 disclose a diamond nitrogen vacancy sensor comprising a diamond having one or more nitrogen vacancies, a loop of conductive material positioned adjacent a portion of the diamond, and a resistor coupled to a first end of the loop and a second end of the loop, the loop and resistor forming a low pass filter for the DNV sensor. The resistor may be modified by a control device or controller.

[0086] From U.S. Pat. No. 8,947,080 B2 a magnetic field sensor is known which detects the Zeeman shift.

[0087] From U.S. Pat. No. 9,599,562 B2, a nanoparticle-diamond-metal compound is known which comprises a diamond nanoparticle having a nitrogen vacancy center and a metallic nanostructure. In this case, the diamond nanoparticle has a predetermined radius and is preferably at least partially directly bonded to a layer of the metallic nanostructure. The nitrogen vacancy center is disposed in the technical teachings of U.S. Pat. No. 9,599,562 B2 at a distance based at least in part on the predetermined radius of the diamond nanoparticle.

[0088] A method for measuring a drillhole is known from U.S. Pat. No. 9,638,821 B2.

[0089] None of the above fonts allow the use of a microwave-free and radio-wave-free sensor system that does not require alignment of the diamond crystal.

[0090] The combination of features of the literature cited in this document with features of the patent literature and non-patent literature cited in this document is an explicit part of the disclosure and, to the extent permitted in the respective legal system of the later nationalizing state of this international application, part of the claiming.

[0091] The disclosure is therefore based on the task of creating a solution that does not have the above disadvantages of the state of the art and has other advantages. This paper discloses several measures that add up to a significant improvement.

[0092] This task is solved by a device according to the independent claims. Further examples of the disclosure and adjacent subject matter are the subject of the subsidiary and subordinate claims.

[0093] The disclosure includes all essential components of a quantum sensing system based on one or more NV centers or one or more groups of NV centers, and methods of making and operating the same.

[0094] For the detection of object positions and/or position changes, for example of mechanical oscillations of an oscillating system (MS), for example, the method presented herein proposes to couple the object, for example the mechanically oscillating system (MS), with a magnetic field in the form of the magnetic flux density B or an electric field in the form of the electric field strength E and to determine the instantaneous value of the magnetic flux density B or of a temporally changing electric flux density D, respectively, by means of a sensor based on quantum mechanical effects.

[0095] According to the disclosure, it was recognized in particular that such quantum mechanical sensor systems, which are preferably based on the measurement of the fluorescence radiation (FL) of paramagnetic centers (NV1), are typically also suitable for the measurement of an electric field with an electric field strength E, which changes in particular with time, if the source of the electric field strength E is moved with respect to the paramagnetic centers (NV1) of the sensor system. Such a movement results in a rotation and distortion of the four-dimensional electromagnetic field strength tensor F_ij in four-dimensional Minkowski space, which transforms the electric field strength E into a magnetic flux density B and thus makes it detectable for such sensor systems based on the detection of the magnetic flux density B.

[0096] Preferably, diamonds with a preferably at least locally very high density of paramagnetic centers (NV1) in the form of NV centers are used as the sensor element or parts of the sensor element in order to ensure a high signal u noise ratio and to exploit quantum mechanical coupling between these paramagnetic centers (NV1). Such HD-NV diamonds with a high density of paramagnetic centers (NV1), in particular NV centers, are discussed below. For example, the diffusion constant for impurity atoms in diamond is close to zero. Thus, these sensor systems with sensor elements comprising diamond have the advantage that no aging phenomena are to be expected for the paramagnetic centers (NV1). The high hardness of diamond ensures the possibility of the high mechanical load without having to fear damage to the sensor element due to abrasion, etc. Thus, the diamond sensor element can be brought into direct contact with materials subject to mechanical wear. For example, direct permanent contact with a high pressure, hot salt water/gas/oil/sand mixture, such as occurs in boreholes, is possible. A high density of paramagnetic centers (NV1), in this case NV centers, typically imparts a red to deep red or black color to a concerned diamond particularly suitable as a sensing element. For example, if such a HD-NV diamond is illuminated with green light as pump radiation (LB), the diamond glows red due to the fluorescence radiation (FL) of the paramagnetic NV centers (NV1). Such a diamond of such a sensor system can be made with a brilliant cut as a jewelry stone. For musical instruments such as electric guitars, the sensor system structure is preferably designed such that only the diamond that glows red in operation is attached in a highly visible manner to evoke a corresponding emotional, positive experience in an observer. The use of decorative diamonds as sensor elements is part of the present disclosure.

[0097] The disclosure therefore firstly comprises a method of producing diamond or a diamond having an at least locally high concentration of NV centers for subsequent use as a sensor element in the sensor systems to be produced. This method is thus of great importance. The term “local” in this context is intended to denote a volume of space as a reference volume within the diamond that is larger than half the pump radiation wavelength (λ_pmp) of the pump radiation (LB) to the third power, since otherwise an arbitrary concentration could already be achieved with a single NV center. Such diamonds are referred to herein and in the following as HD-NV diamonds. The sensing element is a very essential part of the sensing system and thus virtually its foundation. The method first comprises the step of providing the diamond as a diamond blank or diamonds as diamond blanks. The diamonds may be a single diamond as well as a plurality of diamonds. The diamonds may be large or small. The diamonds may also be in powder form or granular form. The diamonds may also be nanocrystalline.

[0098] From M. Capelli, A. H. Heffernan, T. Ohshima, H. Abe, J. Jeske, A. Hope, A. D. Greentree, P. Reineck, B. C. Gibson, Increased nitrogen-vacancy center creation yield in diamond through electron beam irradiation at high temperature, Carbon (2018), doi: https://doi.org/10.1016/j.carbon.2018.11.051, it is known that NV center yield in CVD diamond can be increased by a factor of 2 by heating during electron irradiation with 2 MeV electrons at 710° C.

[0099] The technical teaching of DE 10 2019 117 423.6, which is still unpublished at the time of the application, describes a method for further increasing the yield of NV centers, which describes one way of producing the HD-NV diamonds. These diamonds, in particular those with a NV center density of more than 10 ppm per unit volume, are hereinafter referred to as HD-NV diamonds. It has been shown that a content of more than 20 ppm is better. The content can be determined, for example, by means of EPR (electromagnetic parametric resonance) measurement. Again, we refer the reader to M. Capelli, A. H. Heffernan, T. Ohshima, H. Abe, J. Jeske, A. Hope, A. D. Greentree, P. Reineck, B. C. Gibson, Increased nitrogen-vacancy center creation yield in diamond through electron beam irradiation at high temperature, Carbon (2018), doi: https://doi.org/10.1016/j.carbon.2018.11.051.

[0100] Such diamonds can be used to construct a sensor system with a sensor element, in which the sensor element comprises a substrate (D) or can be the same as this substrate (D). A volume of space may be selected in the substrate (D), the substrate (D) comprising in this volume of space a group (NVC) of paramagnetic centers (NV1) comprising at least two paramagnetic centers (NV1). The sensor system comprises first means (G, PL1), explained in more detail later, for exciting a fluorescence radiation (FL) of said group (NVC) of paramagnetic centers (NV1). The fluorescence radiation (FL) thereby has a fluorescence wavelength (λ_fl). The sensor system further comprises second means (G, F1, PD, M1, TP) for detecting and evaluating the fluorescence radiation (FL). The outer dimensions of the selected volume of space shall not exceed two times the fluorescence wavelength (λfl) when assessing whether a HD-NV diamond is used. The sensor system generates and/or maintains one or more measured values by means of the first and second means (G, PL1, F1, PD, M1, TP) in dependence on the fluorescence radiation (FL) of this group (NVC) of paramagnetic centers (NV1). The fluorescence radiation (FL) depends on a physical parameter. These can be, among others, the magnetic flux density B, the electric flux density D, the acceleration a, the gravitational field strength g, the rotational speed ω, oscillation frequencies ω, the modulation of electromagnetic radiation, the intensity of ionizing radiation, the temperature 9 and the like, as well as their simple and multiple time integrals and derivatives. Thus, the measured value then also depends on the physical parameter. Therefore, this determined measured value can then be used as the measured value of this physical parameter. The device proposed herein at this point is characterized in that the concentration of the paramagnetic centers (NV1) of this group (NVC) in the volume of space is on average greater than 100 ppm and/or 50 ppm and/or 20 ppm and/or 10 ppm and/or 5 ppm and/or 2 ppm and/or 1 ppm and/or 0.5 ppm and/or 0.2 ppm and/or 0.1 ppm and/or greater than 0.01 ppm and/or greater than 0.001 ppm and/or greater than 0.0001 ppm and/or greater than 0.0001 ppm relative to the number of atoms of the substrate (D) per unit volume in said volume of space. Particularly preferably, it is greater than 10 ppm or better than 20 ppm.

[0101] Instead of optical readout via fluorescence radiation (FL), electronic readout via photoelectrons is always possible.

[0102] For this purpose of electronic readout of photoelectrons generated by pump radiation (LB) irradiation, the following alternative sensing device is proposed.

[0103] Such a sensor system with electronic readout comprises a sensor element, wherein again the sensor element comprises or can be equal to a substrate (D) and wherein in the substrate (D) again the volume of space can be selected and wherein the substrate (D) comprises in this volume of space a group (NVC) of paramagnetic centers (NV1). Again, the sensor system comprises first means (G, PL1) for exciting a photocurrent of the photoelectrons of said group (NVC) of paramagnetic centers (NV1) by means of a pump radiation (LB) having a pump radiation wavelength (λ_pmp). In contrast to the sensor system proposed immediately before, the sensor system comprises second means (G, M1, TP) for detecting and for evaluating the photocurrent of the photoelectrons of this group (NVC) of paramagnetic centers (NV1). Now, the external dimensions of the selected volume of space shall not exceed twice the pump radiation wavelength (λ_pmp). The sensor system generates and/or holds one or more measured values by means of the of the first and second means (G, PL1, M1, TP) as a function of the photocurrent. Again, the photocurrent depends on a physical parameter. These can be, among others, the magnetic flux density B, the electric flux density D, the acceleration a, the gravitational field strength g, the rotational speed ω, oscillation frequencies ω, the modulation of electromagnetic radiation, the intensity of ionizing radiation, the temperature ϑ and the like, as well as their simple and multiple time integrals and derivatives. Thus, the measured value also depends on the physical parameter. As before, the measured value is preferably used as the measured value of this physical parameter. Again, the device is characterized in that the concentration of the paramagnetic centers (NV1) of this group (NVC) in the volume of space is on average 100 ppm and/or 50 ppm and/or 20 ppm and/or 10 ppm and/or 5 ppm and/or 2 ppm and/or 1 ppm and/or 0.5 ppm and/or 0.2 ppm and/or greater than 0.1 ppm and/or greater than 0.01 ppm and/or greater than 0.001 ppm and/or greater than 0.0001 ppm and/or greater than 0.0001 ppm relative to the number of atoms of the substrate (D) per unit volume in this space volume. Particularly preferably, it is again greater than 10 ppm or better than 20 ppm.

[0104] In order for the diamonds to later form NV centers, they should have nitrogen atoms, preferably in the form of P1 centers. More simply, the diamonds should preferably be yellow or yellowish. Thus, the diamonds should preferably have a yellow color prior to irradiation, preferably the color “fancy yellow” or “fancy deep yellow” according to the GIA standard of John M. King “Colored Diamonds, colored reference Chart”. Less preferred are diamonds of the GIA classification or “fancy light yellow”, as they contain less nitrogen and accordingly result in diamonds with a lower density of NV centers. The stronger the yellowish color the more densely the NV centers are concentrated in the diamonds later. Less preferably, the diamond blank or blanks comprise nitrogen atoms together with hydrogen, as the latter has a compensating effect. However, such diamonds can be used in a pinch. N-doping with sulfur can also lead to an increase in the yield of NV centers.

[0105] Preferably, the diamonds used here are synthetic HPHT diamond. HPHT stands for High Pressure High Temperature, which means high pressure and high temperature. For the skilled person it is clear that such diamonds are not metastable, i.e., not produced by plasma deposition (CVD diamond). Such HPHT diamonds contain little hydrogen, which from experience is typically not helpful for the formation of NV centers. The method described herein has the advantage that the diamonds can be polished prior to the NV center generation process. If a defect occurs during this process, this material can be discarded prior to treatment in a cost effective manner. A proposed diamond may therefore have at least one or more ground surfaces, for example an optical surface in the form of a first surface (OGL1) for entry and/or exit of radiation, even before irradiation. It is possible that the diamond material irradiated in an irradiation pass described below is a single diamond as well as a plurality of diamonds. The diamonds may be large or small. The diamonds may be in powder form or granular form, or they may be single diamonds. The diamonds may also be nanocrystalline. The use of synthetic CVD diamonds is also possible. However, CVD diamonds have a larger amount of hydrogen, which hinders the formation of the NV centers. It was possible within the scope of the elaboration of the disclosure to generate such NV centers also in CVD diamonds by means of the proposed irradiation method. In this respect, this variant is also claimed here, although it is not optimal. In this variant, the diamond(s) then comprise nitrogen atoms together with hydrogen. Typically, they then do not have a yellow color, but are often transparent as the hydrogen alters the spectral colors.

[0106] The central step in the processing of diamonds is irradiation with high-energy particles. Preferably, high-energy electrons are used. Irradiation with protons, neutrons and helium nuclei is also conceivable and possible.

[0107] Due to the high temperature of the diamonds during irradiation, this irradiation preferably does not take place in air or oxygen, as the diamond would then oxidize to CO₂. Preferably, the irradiation is carried out in a vacuum with a residual pressure of less than 10⁻⁶ mBar. Instead, however, such irradiations have also been carried out in an inert gas atmosphere, in particular in an agon atmosphere, which is not preferred.

[0108] The diamond blanks are thermally coupled to a heat sink via a thermal resistor during irradiation with particles, preferably electrons. The diamond blanks are maintained at the desired process temperature during irradiation by a temperature control device by a controller which is part of the temperature control device. The controller for controlling the temperature of the diamonds during irradiation may be, for example, a PI controller or the like. Preferably, the temperature control device takes into account all energy inputs during irradiation. Preferably, the temperature control device may control one or more thermal energy fluxes into the set of diamond blanks to be processed and/or out of the set of diamond blanks as a function of the targeted and measured average irradiation temperature of the diamond blanks.

[0109] The temperature control device thus preferably controls the total energy input into the diamond blanks and, if necessary, the total energy removal in such a way that the one temperature probe placed in the vicinity of the diamond blanks during the irradiation detects an average irradiation temperature of the diamond blanks of greater than 600° C. and/or greater than 700° C. and/or greater than 800° C. and less than 900° C. and/or less than 1000° C. and/or less than 1100° C. and/or less than 1200° C., very preferably between 800° C. and 900° C. Preferably, for this control, the temperature control device comprises a PD, P or more preferably PID controller.

[0110] Preferably, the total energy input is not constant. Preferably, the total energy input into the diamond blanks has a temporally equal component and, in contrast to the prior art, a temporally pulsed component with a temporal pulse spacing and a pulse height of the total energy input pulses. It is also possible for the total energy pulses to be a single pulse. The temperature control device may then use the DC component and/or the pulse height of the total energy input pulses of the total energy input and/or the temporal pulse spacing of the total energy input pulses to control the average irradiation temperature detected by the temperature probe. Thus, where applicable, a heater may be provided, for example, to increase the total energy input for the pulse duration of a total energy input pulse, resulting in an increase in temperature and improving the healing of radiation damage. The total energy input is composed of the energy from a possibly active heating device, the thermal energy derived via the thermal bleeder resistor and the more or less permanent beam power of the electron beam during irradiation. The temperature control device must take this into account when setting the average target temperature. Any of the previously mentioned components of the total energy input can be used for the proposed control.

[0111] It is useful to cut the diamonds to a known cut, as it then gives the sensor a more refined appearance in the form of a jewelry diamond for use as a sensing element in consumer applications. For example, such a diamond may have one of the following cuts prior to irradiation: Pointed cut, Table cut, Rose cut, Mazarin cut, Brilliant cut, Teardrop cut, Princess cut, Oval cut, Heart cut, Marquise cut, Emerald cut, Asscher cut, Cushion cut, Radiant cut, Old diamond cut, Emerald cut or Baguette cut. In the case of a granule, the diamonds are preferably smaller than 1 mm and/or smaller than 0.5 mm and/or smaller than 0.2 mm and/or smaller than 0.1 mm and/or smaller than 50 μm and/or smaller than 20 μm and/or smaller than 10 μm and/or smaller than 5 μm and/or smaller than 2 μm and/or smaller than 1 μm and/or smaller than 0.5 μm and/or smaller than 0.2 μm and/or smaller than 0.1 μm, whereby the granule is then a powder. The diamonds of such a granulate may also be on average smaller than 1 mm and/or smaller than 0.5 mm and/or smaller than 0.2 mm and/or smaller than 0.1 mm and/or smaller than 50 μm and/or smaller than 20 μm and/or smaller than 10 μm and/or smaller than 5 μm and/or smaller than 2 μm and/or smaller than 1 μm and/or smaller than 0.5 μm and/or smaller than 0.2 μm and/or smaller than 0.1 μm. If a sensor element is to comprise a plurality of diamonds, very small dimensions are useful since the properties of such a diamond powder are generally isotropic, i.e., not directionally dependent, which may be intended in order to obtain a direction-independent sensitivity of the sensor system. To fabricate the sensing element, the diamonds are then mixed with a transparent carrier material (TM) that then solidifies to form the sensing element. We refer here to the as yet unpublished international patent application PCT DE 2020 100 430. Exemplary carrier materials mentioned here include UHU and gelatin and glass, in particular a glass frit. Typically, the carrier material (TM) in the solidified state is transparent to pump radiation (LB) and fluorescence radiation (FL). If, for example, a magnetic flux density B is to be detected by means of the intensity (I_fl) of the fluorescence radiation (FL) of the paramagnetic centers (NV1), the support material (TM) preferably does not shield the paramagnetic centers (NV1) of the sensor element against the action of this physical quantity to be detected, in this case the magnetic flux B.

[0112] Otherwise, it may be desired to use a single crystal, such as a diamond crystal, as the sensing element and precisely align that single crystal to detect particular resonances (e.g., GSLAC) in the sensor system package to make those particular features measurable. In that case, it may be useful to use a larger crystal as a single sensing element.

[0113] The preferred method for producing diamonds with high NV center density is, as indicated earlier, irradiating the diamond and/or diamonds with particles of high energy.

[0114] Preferably, the irradiation takes place in a quartz vessel in which the diamonds in the form of the diamond blanks are then placed for irradiation. The quartz vessel is preferably open at the top for the particle beam entry. A temperature sensor, for example a thermocouple, is preferably placed in or on the diamonds during the irradiation to provide an actual temperature value for controlling the processing temperature of the diamonds during the irradiation.

[0115] Preferably, the diamond(s) is/are irradiated with electrons, as these can completely penetrate the diamonds in a reasonably homogeneous manner if the energy is sufficiently high. Preferably, the energy of the electrons of the electron beam is greater than 500 keV and/or greater than 1 MeV and/or greater than 3 MeV and/or greater than 4 MeV and/or greater than 5 MeV and/or greater than 6 MeV and/or greater than 7 MeV and/or greater than 9 MeV and/or greater than 10 MeV and/or greater than 10 MeV, an energy of 10 MeV being clearly the most preferred at present as the optimum in the apparatus used to elaborate the disclosure. An energy of the particles greater than 20 MeV should be avoided, otherwise radioactive activation of the diamond material may occur. The irradiation dose for this irradiation with electrons is preferably between 5*10¹⁷ cm⁻² and 2*10¹⁸ cm⁻², but at least below 10¹⁹ cm⁻². It is important that, in this case, the temperature of the diamond or diamonds is kept at a temperature greater than 600° C. and/or greater than 700° C. and/or greater than 800° C. and less than 900° C. and/or less than 1000° C. and/or less than 1100° C. and/or less than 1200° C. by temperature control during the irradiation with these electrons. Preferably, however, according to the experiences during the elaboration of the present disclosure, the optimum temperature is between 800° C. and 900° C. With other temperatures, other centers in the diamond are preferably established. In the temperature control, the heating by the first heating energy flow of a typically present external heater and by the second heating energy flow of the typically however neglected heating by the electron beam current must be taken into account. The heating by these heating energy currents is opposed by the cooling energy current of the cooling by heat dissipation into a heat sink. The beam current of the electric current of these electrons of the electron beam is now preferably set or controlled in such a way that the irradiation period for achieving the above irradiation dose is at least 0.05 days and/or at least 0.5 days and/or at least 1 day and/or at least 2 days and/or at least 4 days and/or at least 8 days. In the example, 2 days of irradiation duration was used for very successful experiments. Preferably, because of the cost of such a facility, a pulsed linear accelerator (linac) is used for irradiation with a design pulsed electron beam. The heating energy of the electron beam is determined by the energy of the electrons and the average beam current. The heating energy supplied during irradiation is dissipated into a heat sink via said thermal bleeder resistor. Preferably, the total heating energy supplied is controlled by means of a thermal sensor sensing the temperature of the of the diamond blanks during irradiation and by means of a controller controlling a, preferably the substantial, heating energy flow to establish a desired processing temperature of the diamonds within a target temperature band around the target temperature for the diamond blanks during irradiation. Preferably, the controlled heating energy flow that heats the diamond blanks during irradiation is pulse modulated in whole or in part at least intermittently. I.e., it is supplied in heating pulses. That is, it varies in a pulsed manner over time between a first energy current value supplied to the diamond blanks in a first time period of a temporal pulse period of the pulse modulation and a second energy current value supplied to the diamond blanks in a second time period of the temporal pulse period of the pulse modulation during the irradiation. Preferably, the first energy current value is different from the second energy current value. Preferably, the control is performed by adjusting the heating pulse amplitude, the heating pulse width, the heating pulse spacing or the duty cycle of the pulse modulation of the heating pulses, that is, by a method of pulse modulation. The duty cycle is also referred to as the duty cycle.

[0116] With the above described process, depending on the nitrogen and hydrogen content of the diamond blanks prior to irradiation, diamond with a NV center density of more than 500 ppm and/or of more than 200 ppm and/or of more than 100 ppm and/or of more than 50 ppm and/or of more than 20 ppm and/or of more than 10 ppm and/or of more than 5 ppm and/or of more than 2 ppm and/or of more than 1 ppm and/or of more than 0.1 ppm and/or of more than 0.01 ppm and/or of more than 10 ppm⁻³ and/or of more than 10 ppm⁻⁴ and/or of more than 10 ppm⁻⁵ and/or of more than 10 ppm⁻⁶ with respect to the number of carbon atoms per unit volume. Such diamonds are particularly suitable as sensing elements of the proposed devices and for other quantum technological devices. Preferably, during irradiation, the typically LINAC specific unavoidable pulsation of the electron beam and thus its heating energy is stabilized by a control system in order to obtain predictable results. Instead of irradiation with electrons, irradiation with protons or helium nuclei or other particles, e.g., neutrons, can also be performed, which then provide the diamond with NV centers only superficially, if necessary, due to the lower penetration depth, which can be advantageous. Such a diamond then shows traces of irradiation with particles, in particular with electrons and/or protons and/or helium, irrespective of the type of particles used. In one example, preferably the provided diamond or an epitaxial layer of sufficient thickness on at least one surface of the diamond is isotopically pure. Here, “isotopically pure” as used herein means that more than 99.5% of the atoms of the diamond can be assigned to a carbon isotope, preferably the nuclear spin free ¹²C isotope. This leads to few interfering nuclear spins of ¹³C-atoms. The thickness of an epitaxial layer is sufficient if the paramagnetic centers (NV1) in this layer behave as if the diamond surrounding them were entirely isotopically pure.

[0117] Diamonds with a high density of NV centers, as described, are hereinafter referred to as HD-NV diamonds.

[0118] Preferably, the high density of the paramagnetic centers (NV1) is realized only in a small volume within the sensor element, for example the diamond, with preferably high intensity (I_pmp) of the pump radiation (LB), since the nonlinearity of the intensity (I_fl) of the fluorescence radiation (FL) of the paramagnetic centers (NV1), would otherwise lead to a reduction of the contrast (KT).

[0119] Finally, it should be mentioned that the irradiation can also take place only locally. If, for example, in a diamond the nitrogen atoms have only been introduced in a thin plane by ion implantation, the electron beam can only irradiate the crystal along spaced axes. A similar situation is possible for other materials and centers if they can be produced by ion implantation followed by electron or particle irradiation. Only at the crossing points between these irradiation axes and the layer of implanted nitrogen atoms, paramagnetic centers (NV1) are formed in the example of NV centers in diamond if the parameters are chosen correctly. In this way, for example, superlattices of groups (NVC) of paramagnetic centers (NVC) can be formed. Each group (NVC) of paramagnetic centers (NV1) in this superlattice may represent a material having a high density of paramagnetic centers (NV1) within the respective group. In the case of groups of NV centers in diamond, the material of the groups of NV centers is thus preferably HD-NV diamond, which preferably has a density of NV centers within the respective group of more than 10 ppm or better more than 20 ppm.

[0120] The proposed sensor system now preferably uses the HD NV diamonds thus produced with a respective high density of NV centers, for example in the form of red jewelry diamonds, as sensor elements for the sensor systems presented hereinafter, which detect the intensity (I_fl) of the fluorescence radiation (FL) of the NV centers when irradiated with green light as pump radiation (LB). Green light is used in the technical teachings of this paper for pumping the paramagnetic centers (NV1), here typically the NV centers in diamond. Instead of the term “green light”, the equivalent term “green pump radiation (LB)” is also used in this writing. The pump radiation (LB) has a pump radiation wavelength (λ_pmp) of this “green light”. The pump radiation (LB) causes the respective paramagnetic center (NV1) or paramagnetic centers (NV1) or group or groups (NVC) of paramagnetic centers (NV1) to emit fluorescence radiation (FL) having a fluorescence wavelength (λ_fl) upon irradiation with the pump radiation (LB) of the pump radiation wavelength (λ_pmp). Typically, when NV centers in diamond are used as paramagnetic centers (NV1), the fluorescence wavelength (λ_fl) of the fluorescence radiation (FL) of the NV centers is such that they appear red. It has been shown that, in connection with NV centers in diamond as paramagnetic centers, light having a pump radiation wavelength (λ_pmp) of the pump radiation (LB) of at most 700 nm and at least 500 nm is in principle particularly suitable as pump radiation (LB), i.e., as “green light”. In connection with the use of other materials for the sensor element and correspondingly other paramagnetic centers, completely different wavelength ranges of the pump radiation wavelength (λ_pmp) of the pump radiation (LB) can perform the same functions in the sensor system then modified in this way. Therefore, the NV centers herein represent only one example of one example of such a paramagnetic center (NV1). In this respect, “green light” or “green pump radiation (LB)” shall be understood herein as a function definition, where the function shall be understood as equivalent to the function in the system using NV centers in diamond as paramagnetic centers (NV1) in a sensor element. In particular, when using a NV center as a paramagnetic center (NV1), the “green light” or “green pump radiation” should have a pump radiation wavelength (λ_pmp) in a wavelength range from 400 nm to 700 nm wavelength and/or more preferably 450 nm to 650 nm and/or more preferably 500 nm to 550 nm and/or more preferably 515 nm to 540 nm. In this regard, a wavelength of 532 nm is clearly preferred as the pump radiation wavelength (λ_pmp). Light or electromagnetic pump radiation (LB) used in the use of paramagnetic centers (NV1) other than NV centers in diamond to perform the same functions is also referred to herein as “green light” or “green pump radiation”. In this respect, such examples are encompassed by claims in which “green light” or “green pump radiation” is referred to, even if to a human such radiation does not appear to be colored green. Thus, the proposed sensor system is also applicable to other suitable paramagnetic centers, such as ST1 center, SiV center, GeV center, TR1 center etc., applicable. However, the NV center in diamond is particularly suitable and particularly good to be fabricated, e.g., as described above, and in high density with high fabrication yield.

[0121] Suitably, the pump radiation (LB) of the pump radiation source (PL1), preferably a laser, is pulsed in dependence on a pulsed alternating component (S5w) of a transmission signal (S5). The pulsed alternating component (S5w) of a transmission signal (S5) is used as a measurement signal (MES), i.e. as a reference signal for a look-in amplifier, in order to amplify with low noise the modulation of the intensity (I_fl) of the fluorescence radiation (FL) converted into modulated electric currents, in particular photoelectron currents or voltages, for example of a receiver output signal (S0).

[0122] According to the disclosure, it was recognized that the pulsed pulse modulation of the pump radiation (LB) and thus the pulsed pulse modulation of the alternating component (S5w) of the transmission signal (S5) should preferably not have a 50% duty cycle. (See FIG. 91) The alternating component (S5w) of the transmission signal (S5) has an amplitude (S5WA) of the alternating component (S5w) of the transmission signal (S5). At the beginning of a transmission signal period (TP), the value of the transmission signal (S5) is at the value of the direct component (S5g) of the transmission signal (S5) minus the value of the amplitude (S5WA) of the alternating component (S5w). The value of the transmission signal (S5) then increases to the value of the sum of the value of the amplitude (S5WA) of the alternating component (S5w) of the transmission signal (S5) plus the value of the direct component (S5g) of the transmission signal (S5). For a transmission signal plateau time (T_S5pmpp), the value of the transmission signal (S5) then remains substantially at this value level, in order to then drop with a transmission signal decay time (T_S5pmpd) to the value from the difference value of the direct component (S5g) of the transmission signal (S5) minus the value of the amplitude (S5WA) of the alternating component (S5w) of the transmission signal (S5). The value of the transmission signal (S5) then remains substantially at this value until the end of the transmission signal period (TP), when the value of the transmission signal (S5) increases again with a transmission signal rise time (T_S5pmpr) to the value of the sum of the amplitude (S5WA) of the alternating component (S5w) of the transmission signal (S5) plus the value of the direct component (S5g) of the transmission signal (S5). Preferably, the maximum value of the pulses of the alternating component (S5w) of the transmission signal (S5) in terms of the sum of the amplitude (S5WA) of the alternating component (S5w) of the transmission signal (S5) plus the value of the direct component (S5g) of the transmission signal (S5) is maximized to achieve a maximum intensity (I_pmp) of the pump radiation (LB) at the times when the pump radiation source (PL1) emits pump radiation (LB). The purpose of this is that the contrast (KT) (see FIG. 28) does not depend linearly on the intensity (I_pmp) of the pump radiation (LB) reaching the paramagnetic centers (NV1) and increases towards large intensities (I_pmp) of pump radiation (LB). This is known for single NV centers in diamond, i.e., not for HD-NV diamonds as described here, for example, from the paper Staacke, R., John, R., Wunderlich, R., Horsthemke, L., Knolle, W., Laube, C., Glösekötter, P., Burchard, B., Abel, B., Meijer, J. (2020), “Isotropic Scalar Quantum Sensing of Magnetic Fields for Industrial Application,” Adv. Quantum Technol. doi: 10.1002/qute.202000037. We refer in particular to FIGS. 3b and 3d of that paper. By having a high density of paramagnetic centers (NV1), such as by having a high density of NV centers as in an HD-NV diamond as described in that paper, the contrast (KT) can be increased beyond that shown in that paper, which is new compared to the prior art.

[0123] The duty cycle of the transmission signal (S5) and thus of the modulated transmission signal (S5w) is defined here as the transmission signal pulse duration (T_S5pmp) divided by the transmission signal period (T_P). The transmission signal pulse duration (T_S5pmp) plus the transmission signal complementary time (T_S5c) are equal to the transmission signal period (T_P).

[0124] Preferably, the alternating component (S5w) of the transmission signal (S5) and thus the transmission signal (S5) is pulse-modulated with a duty cycle of the alternating component (S5w) of the transmission signal (S5) of less than 50% and/or preferably less than 40% and/or preferably less than 30% and/or preferably less than 20% and/or preferably less than 10%. Preferably, therefore, the pulse is an ultrashort pulse with as high an amplitude as possible.

[0125] Accordingly, preferably the modulated transmission signal (S5w) is pulse-modulated with a duty cycle smaller than 50% and/or preferably smaller than 40% and/or preferably smaller than 30% and/or preferably smaller than 20% and/or preferably smaller than 10%. Preferably, therefore, the pulse is an ultrashort pulse. This ultrashort pulse is preferably converted, with the greatest possible amplification, into a corresponding short intensity pulse of the intensity (I_pmp) of the pump radiation (LB), which is as intense as possible.

[0126] Since the pump radiation source (PL1) is driven by the transmission signal (S5), it typically reproduces essentially the transmission signal (S5) delayed by a transmission delay (Δt I_pmp). For the calculation of many applications, this transmission delay (Δt_Ipmp) can be assumed to be 0 s for simplification.

[0127] In this case, the pump radiation pulse duration (T_Ipmp) is defined here in such a way.

• • [0128] that the intensity pulse of the intensity (I_pmp) of the pump radiation (LB) has a pump radiation intensity maximum (I_pmpmax) and
  • [0129] that the pump radiation pulse duration (T_Ipmp) of an intensity pulse of the pump radiation (LB) starts at the first time of exceeding 50% of the intensity value of the pump radiation intensity maximum (I_pmpmax) minus the possibly existing bias value (I_pmpoff) of the intensity (I_pmp) of the pump radiation (LB), by the instantaneous intensity (I_pmp) of the intensity pulse of the pump radiation (LB) minus the possibly existing bias value (I_pmpoff) of the intensity (I_pmp) of the pump radiation (LB) and
  • [0130] in that the pump radiation pulse duration (T_Ipmp) of an intensity pulse of the pump radiation (LB) ends with the second time point of falling below 50% of the intensity value of the pump radiation intensity maximum (I_pmpmax) minus the possibly existing bias value (I_pmpoff) of the intensity (I_pmp) of the pump radiation (LB) by the bias value (I_pmpoff) of the intensity pulse of the pump radiation (LB) minus the possibly existing bias value (I_pmpoff) of the pump radiation (LB).

[0131] The pump radiation rise time (T_Ipmpr) of the intensity (I_pmp) of the pump radiation (LB) is defined here in such a way.

• • [0132] that the pump radiation rise time (T_Ipmpr) of an intensity pulse of the pump radiation (LB) starts with the first time of exceeding 10% of the intensity value of the pump radiation intensity maximum (I_pmpmax) minus the possibly existing bias value (I_pmpoff) of the intensity (I_pmp) of the pump radiation (LB), by the instantaneous intensity (I_pmp) of the intensity pulse of the pump radiation (LB) minus the possibly existing bias value (I_pmpoff) of the intensity (I_pmp) of the pump radiation (LB) and
  • [0133] that the pump radiation rise time (T_Ipmpr) of an intensity pulse of the pump radiation (LB) ends with the third time of exceeding 90% of the intensity value of the pump radiation intensity maximum (I_pmp) minus the possibly existing bias value (I_pmpoff) of the intensity (I_pmp) of the pump radiation (LB) minus the possibly existing bias value (I_pmpoff) of the intensity (I_pmp) of the pump radiation (LB) by the instantaneous intensity (I_pmp) of the intensity pulse of the pump radiation (LB) minus the possibly existing bias value (I_pmpoff) of the intensity (I_pmp) of the pump radiation (LB).

[0134] The pump radiation decay time (T_Ipmpd) of the intensity (I_pmp) of the pump radiation (LB) is defined here in such a way.

• • [0135] that the pump radiation decay time (T_Ipmpd) of an intensity pulse of the pump radiation (LB) begins with the first time of falling below 90% of the intensity value of the pump radiation intensity maximum (I_pmpmax) minus the possibly existing bias value (I_pmpoff) of the intensity (I_pmp) of the pump radiation (LB) by the instantaneous intensity (I_pmp) of the intensity pulse of the pump radiation (LB) minus the possibly existing bias value (I_pmpoff) of the intensity (I_pmp) of the pump radiation (LB) and
  • [0136] that the pump radiation decay time (T_Ipmpd) of an intensity pulse of the pump radiation (LB) ends with the third time of falling below 10% of the intensity value of the pump radiation intensity maximum (I_pmpmax) minus the possibly existing bias value (I_pmpoff) of the intensity (I_pmp) of the pump radiation (LB) by the instantaneous intensity (I_pmp) of the intensity pulse of the pump radiation (LB) minus the possibly existing bias value (I_pmpoff) of the intensity (I_pmp) of the pump radiation (LB).

[0137] For the calculation of many applications, the transmit delay (Δt_Ipmp) can be assumed to be 0 s and/or the pump radiation decay time (T_Ipmpd) can be assumed to be 0 s and/or the transmission signal decay time (T_S5pmpd) can be assumed to be 0 s and/or the pump radiation rise time (T_S5pmpr) can be assumed to be 0 s for simplicity. The pump radiation pulse duration (T_Ipmp) is then equal to the transmission signal pulse duration (T_S5pmp). The pump radiation pulse duration (T_Ipmp) and the transmission signal pulse duration (T_S5pmp) are then equal to the first times (T1) at which the transmission signal (S5) is active and the pump radiation source (PL1) emits pump radiation (LB). Under these simplifications, the transmission signal complementary time (T_S5c) and the pump radiation complementary time (Tic) are equal to the second times (T2) at which the transmission signal (S5) is not active and the pump radiation source (PL1) does not emit pump radiation (LB).

[0138] Thus, the first times (T1) and the second times (T2) in FIGS. 6, 11, 13, 19, 23 and 26 are only a simplification for better understanding. The levels of FIGS. 6, 11, 13, 19, 23 and 26 are thus only exemplary and serve only for a better understanding.

[0139] To maximize the contrast (KT), the temporal duration of the pump radiation fall time (T_Ipmpd) and/or the pump radiation rise time (T_Ipmpr) should each be no more than 25%, preferably no more than 10%, preferably no more than 5%, preferably no more than 2% of the temporal duration of an intensity pulse of the pump radiation (LB), i.e. the pump radiation pulse duration (T_Ipmp).

[0140] Thus, in order to maximize the contrast (KT), the temporal duration of the transmission signal fall time (T_S5pmpd) and/or the transmission signal rise time (T_S5pmpr) should each be not more than 25%, preferably not more than 10%, preferably not more than 5%, preferably not more than 2% of the temporal transmission signal pulse duration (T_S5pmp).

[0141] In order to achieve such short rise and fall times, various writings are known from the prior art, which are mentioned here only by way of enumeration and whose technical teachings can be used here.

[0142] A driver circuit for an LED is known from DE 10 2009 060 873 A1. A driver circuit for light-emitting optoelectronic components is known from DE 10 2016 116 368 A1 (see FIG. 1 of DE 10 2016 116 368 A1), in which the charging circuit (reference signs 2, 3, 4, 5, 9, 10, 11, 12, 13, 14 of DE 10 2016 116 368 A1) charges a capacitor (reference signs 18-21 of DE 10 2016 116 368 A1) via a series resistor (reference sign 3 of DE 10 2016 116 368 A1). The light-emitting optoelectronic components (reference signs 22 to 25 of DE 10 2016 116 368 A1) are connected together with their cathodes to form a first star point. A drive switch (reference character 26 of DE 10 2016 116 368 A1) connects this star point to the reference potential (reference character GND of DE 10 2016 116 368 A1) when one or more of the light-emitting optoelectronic components is to emit light. The buffer capacitor (reference sign 9 of DE 10 2016 116 368 A1) serves to quickly charge the actual energy reserves (reference signs 18 to 21 of DE 10 2016 116 368 A1).

[0143] U.S. Pat. No. 10,193,304 B2 discloses a driver circuit in which the capacitors are charged in such a way that the current remains below the response threshold of the lasers.

[0144] From EP 3 301 473 A1, a drive circuit for a single LED suitable for emitting short pulses is known.

[0145] DE 10 2016 116 369 A1 discloses an LED driver circuit in which each LED has its own drive switch.

[0146] DE 10 2008 021 588 A1 describes a laser drive circuit in which several drive switches are connected in parallel so that they can generate pulses with a time delay and cool down between the pulses, while the other drive switches can generate the other pulses.

[0147] From DE 10 2017 121 713 A1, trigger switches are known, which comprise subunits in which each subunit has its own capacitor for providing the switching energy.

[0148] Control devices for a gas laser are known from DE 19 914 362 A1 and DE 19 514 062 A1.

[0149] From U.S. Pat. No. 9,185,762 B2 (DE 10 2014 105 482 A1), a circuit for reducing the turn-off time of a laser diode is known.

[0150] From DE 10 2017 100 879 A1, a circuit for rapidly switching a single laser diode on and off is known.

[0151] From DE 10 2018 106 860 A1, the direct connection between a laser die of a single laser and the die of an integrated drive switch is known. The control switch is connected between the supply voltage and the anode of the laser diode.

[0152] From DE 10 2016 116 875 A1, a driver circuit (e.g. FIG. 12 of DE 10 2016 116 875 A1) with a common drive switch (reference sign S3 of DE 10 2016 116 875 A1) for a plurality of lasers (reference signs D1, D7 of DE 10 2016 116 875 A1) is known, in which the common drive switch (reference sign S3 of DE 10 2016 116 875 A1) is connected to the cathodes of the lasers and can connect them to the reference potential. In this case, the energy for the laser pulse comes from a common storage capacitance (reference sign C of DE 10 2016 116 875 A1). The lasers are selected via separate switches (reference sign S2 of DE 10 2016 116 875 A1).

[0153] DE 10 2006 036 167 B4 discloses a laser driver circuit in which the resonances of the parasitic inductors and the capacitors are tuned to support predetermined characteristics of the light pulses to be generated.

[0154] U.S. Pat. No. 6,697,402 B2 discloses a laser driver with laser current detection via a shunt resistor between the cathode terminal and the reference potential.

[0155] A single driver circuit is known from U.S. Pat. No. 6,697,402 B2. A coil is used as an energy storage device.

[0156] From DE 10 2018 106 861 A1, the driving of a laser diode with an H-bridge is known.

[0157] From DE 19 546 563 C2 a driver circuit is known in which the charging circuit is disconnected by an inductance from the laser diode for the short time of the light pulse emission when the drive transistor initiates the light emission.

[0158] Preferably, in order to avoid thermal overload of the pump radiation source (PL1), for example a semiconductor laser, the pump radiation pulse period (T_Ipmp) should be less than 50% of the transmission signal period (T_P) of the alternating component (S5w) of the transmission signal (S5).

[0159] Thus, the transmission signal pulse period (T_S5pmp) should preferably be less than 50% of the transmission signal period (T_P) of the alternating component (S5w) of the transmission signal (S5).

[0160] Since, to a first approximation, the alternating component of the intensity (I_pmp) of the pump radiation (LB) of the pump radiation source (PL1) is likely to be proportional to the alternating component (S5w) of the transmission signal (S5), it can be assumed for the purposes of this paper, that the above conditions for the alternating component (S5w) of the transmission signal (S5) also apply to the time characteristic of the intensity (I_pmp) of the pump radiation (LB) if, during a measurement, the time characteristic of the electric current and/or of the electric voltage of the alternating component (S5w) of the transmission signal (S5) satisfies the same 10%, 90% and 50% conditions with respect to pulse duration, rise time and fall time respectively.

[0161] It was further recognized in accordance with the disclosure that, in contrast to the prior art, microwave radiation is not necessary for operation of the sensor systems proposed herein in order for the paramagnetic centers (NV1) thus excited to a high level to drop to an intermediate level. Rather, it is sufficient if the sensing element, for example the diamond crystal of a HD NV diamond, has a sufficiently high density of paramagnetic centers (NV1), for example NV centers in diamond. If the average distances between paramagnetic centers (NV1) excited with pump radiation (LB), that is, for example, between the NV centers, are small enough, they couple and enhance the dependence of the intensity (I_fl) of their fluorescence radiation (FL) on the magnetic flux density B or other physical parameters affecting the fluorescence radiation (FL) at the location of the paramagnetic centers (NV1). Preferably, an exemplary diamond crystal in the form of a HD-NV diamond has a NV center density of more than 0.01 ppm based on the number of carbon atoms per unit volume of the diamond crystal. Of course, lower concentrations of paramagnetic centers (NV1), here exemplarily of NV centers, such as of more than 0.01 ppm and/or of more than 10-3 ppm and/or of more than 10⁻⁴ ppm and/or of more than 10⁻⁵ ppm and/or of more than 10⁻⁶ ppm relative to the atoms of the substrate (D) in the sensor element per unit volume can also be used. However, the intensity (I_fl) of the fluorescence radiation (FL) then attenuates more and more as the concentration of NV centers in the diamond crystal decreases, so that more and more stringent requirements have to be imposed on the electronic signal post-processing. The said density of paramagnetic centers (NV1) need not be achieved everywhere in the sensing element, i.e., the exemplary diamond. It has been recognized in the course of the disclosure that it is rather preferably sufficient, indeed advantageous, if this density is exceeded only locally and the intensity (I_pmp) of the pump radiation (LB) is preferably maximized only there in this region of high NV center density, as the region of high density of paramagnetic centers (NV1). Thus, preferably more than 100, more preferably more than 1000, more preferably more than 10⁴, more preferably more than 10⁵, more preferably more than 10⁶, more preferably more than 10⁷ paramagnetic centers (NV1) within a sensor element are used in parallel and preferably coupled to each other for the operation of the sensor system. Due to the high density of the paramagnetic centers (NV1) in the substrate (D) within the sensor element, for example the NV centers of a HD-NV diamond, the spins of the electron configurations of the excited NV centers, i.e. the paramagnetic centers (NV1), influence each other, so that collective effects, similar to but not identical to those in a ferromagnet, occur. By spontaneous emission, some of the paramagnetic centers (NV1) then always spontaneously assume an energetically lower intermediate state after a transition time ta coming from the excited state, which in the prior art is typically only achieved by using microwave radiation.

[0162] It has thus been recognized, as previously described, in accordance with the disclosure, that the high density of paramagnetic centers (NV1)—when HD-NV diamond is used, due to a high density of NV centers—eliminates and thus saves the need for device parts for generating and introducing the microwave radiation. Nonetheless, the use of microwave antennas and transmitters is useful when additional modulation of fluorescence radiation (FL) from the paramagnetic center (NV1) or paramagnetic centers or a group or groups (NVC) of paramagnetic centers (NV1) is desired or when lower density paramagnetic center (NV1) diamonds are to be used. By omitting microwave radiation, such sensor systems as those presented here only become useful for use in biological and, in particular, medical applications. Otherwise, radiation exposure of the surrounding tissue by the microwave radiation occurs, which massively limits the use of sensors with microwave excitation of the excited paramagnetic centers to an intermediate level for such purposes.

[0163] Preferably, the sensor element is provided with an anti-reflective coating and/or matching layer (ASv) for radiation of the pump radiation wavelength (λ_pmp) of the pump radiation (LB) of the pump radiation source (PL1). In the case of a HD-NV diamond as sensor element, preferably the first surface (OFL1) of the diamond which is irradiated with the pump radiation (LB) is provided with an anti-reflective coating or a matching layer (ASv) and/or a functionally equivalent microstructuring and/or coating of equivalent effect.

[0164] The shape of the sensor element can thus be selected more or less freely. Large sensor element areas are also possible.

[0165] The core of the proposed sensor system is a sensor element with an at least locally high density of paramagnetic centers (NV1), for example an HD-NV diamond. Among other things, this sensor element substantially distinguishes the proposals presented herein from the prior art. In a proposed sensing system, a pump radiation source (PL1) is provided and adapted to emit pump radiation (LB) that can excite the selected paramagnetic center (NV1) to emit fluorescent radiation (FL). In the case of NV centers in diamond or in diamonds, a laser diode of Osram type PLT5 520B is suitable, for example, as a pump radiation source (PL1) with 520 nm pump radiation wavelength (λ_pmp). The pump radiation (LB) of the pump radiation source (PL1) should have a pump radiation wavelength in a wavelength range of 400 nm to 700 nm wavelength and/or better 450 nm to 650 nm and/or better 500 nm to 550 nm and/or better 515 nm to 540 nm when NV centers are used. Pump radiation of this feature is referred to herein as “green” pump radiation (LB). Clearly, a wavelength of 532 nm is preferred as the pump radiation wavelength (λ_pmp) of the pump radiation (LB) when using NV centers. 520 nm has also been successfully used. For cost reasons, the pump radiation source (PL1) is preferably a light emitting diode or a laser, which are also collectively referred to hereinafter as LEDs for simplicity. It is conceivable to use other light emitting devices, for example organic light emitting diodes (OLEDs) or electroluminescent devices, as pump radiation sources (PL1). However, the use of LEDs as pump radiation sources (PL1) is clearly more advantageous at present.

[0166] The paramagnetic center (NV1) in the material of the sensor element emits said fluorescence radiation (FL) when irradiated with said pump radiation (LB), which is typically green in the case of NV centers as paramagnetic centers (NV1). The fluorescence radiation (FL) is typically red in the case of using NV centers as paramagnetic centers (NV1). Typically, in the negatively charged state NV⁻, the NV center emits⁻ fluorescence radiation (FL) with a fluorescence radiation wavelength (λfl) of 637 nm. In the non-negatively charged state, NV centers do not fluoresce. The location of the Fermi level at the site of the paramagnetic center in question (NV1) here of an NV center, determines the preferred charge state of the paramagnetic center, here of the NV center. By embedding the paramagnetic center (NV1) in an electric field generated, for example, by a line (LH), the preferred charge state of the paramagnetic center, for example, of an NV center, can be predetermined. Thus, it is possible to modulate the intensity (I_fl) of the fluorescent radiation (FL) of a paramagnetic center, for example an NV center, by selectively bringing the paramagnetic center (NV1) into a fluorescent state, for example the N⁻ state, or into another non-fluorescent state. In a fluorescent state, the paramagnetic center (NV1) in question emits fluorescent radiation of the fluorescent radiation wavelength (λ_fl) when irradiated with pump radiation (LB) of the pump radiation wavelength (λ_pmp). In a non-fluorescent state, the respective paramagnetic center (NV1) does NOT emit fluorescence radiation of the fluorescence radiation wavelength (λ_fl) when irradiated with pump radiation (LB) of the pump radiation wavelength (λ_pmp).

[0167] This fluorescence radiation (FL) of the one or more paramagnetic centers (NV1) or of the group of the groups (NVC) of paramagnetic centers (NV1) is detected by the radiation receiver (PD). The radiation receiver (PD) is, for example, a photodiode which is preferably furthermore sensitive to radiation at a compensation radiation wavelength (λ_ks), explained later, of a compensation radiation source (PLK), also explained later, or preferably furthermore sensitive to the compensation fluorescence wavelength (λ_kfl), explained later, of the compensation fluorescence radiation (KFL), also explained later, of one or more reference paramagnetic centers (NV1) or of a group or groups (NVC), also explained later, of paramagnetic reference centers (NV2).

[0168] The radiation receiver (PD), for example said photodiode, is sensitive to radiation of the fluorescence radiation wavelength (λfl) of the fluorescence radiation (FL). As a photodiode, as a radiation receiver (PD), for example a PIN photodiode of the type BPW 34 FA of the company Osram was used in the elaboration of the disclosure. In the case of the use of NV centers, the radiation receiver (PD) is thus preferably sensitive to radiation having a fluorescence radiation wavelength (λfl) of 637 nm. For example, by using an upstream optical filter (F1), preferably the combination of the optical filter (F1) and the radiation receiver (PD) is not sensitive to radiation having the pump radiation wavelength (λ_pmp) transmitted or reflected by the sensing element, for example. In the case of NV centers in diamond as paramagnetic centers (NV1), for example, this would optimally be a pump radiation wavelength (λ_pmp) of 532 nm for which the radiation receiver (PD) in combination with the first filter (F1) would then not be sensitive.

[0169] The pump radiation source (PL1) generates the pump radiation (LB) depending on the current value of a transmission signal (S5). The sensor system is thereby preferably designed in such a way that the pump radiation (LB) is at least partially irradiating the paramagnetic center or centers (NV1). As described above, optical functional elements such as optical waveguides, reflectors, lenses, prisms, free air gaps, vacuum gaps, apertures, mirrors, beam sections, gratings, etc. may be used for this purpose, which optically couple the pump radiation source (PL1) to the paramagnetic center or centers (NV1) of the sensor element. Similarly, the sensor system is preferably designed such that the fluorescent radiation (FL) at least partially irradiates the radiation receiver (PD). This can also be ensured by means of said optical functional elements mentioned in this writing, which optically couple the paramagnetic center(s) (NV1) of the sensor element to the radiation receiver (PD).

[0170] The radiation receiver (PD) generates, as a function of the intensity value of the intensity of the total irradiation and thus, inter alia, as a function of the intensity value of the intensity (I_fl) of the fluorescence radiation (FL) incident thereon, a receiver output signal (S0) whose instantaneous value (s0) depends on the instantaneous value of the intensity of the total incident radiation and thus on the instantaneous value of the intensity (I_fl) of the fluorescence radiation (FL). An evaluation circuit converts the sequence of instantaneous values (s0) of the receiver output signal (S0) into a measured value for the amplitude and/or intensity (I_fl) of the fluorescent radiation (FL). This measured value is output or provided for use as an instantaneous value (s4) of the sensor output signal (out). Since the intensity (I_fl) of the fluorescence radiation (FL) of the paramagnetic centers (NV1) depends on physical parameters such as, for example, the magnetic flux density B at the location of these paramagnetic centers (NV1), it is thus possible to construct, for example, a simple magnetometer with high spatial and/or temporal resolution as an example of a sensor system for detecting a physical parameter by means of a paramagnetic center (NV1) whose sensor element has little noise and which has a high sensitivity. Further physical parameters in addition to the magnetic flux density B, which could possibly be measured in this way by means of the intensity (I_fl) of the fluorescence radiation (FL) of the paramagnetic center (NV1), would be, for example, electric flux density D, acceleration a, gravitational field strength g, pressure P, temperature ϑ, rotational speed ω, oscillation frequency of mechanical parts (beams), position, intensity of ionising radiation, etc., which could be measured in this way by means of the intensity (I) of the fluorescence radiation (FL) of the paramagnetic center (NV1).

[0171] More specific examples of the implementation of such a sensor system are provided below. Preferably, such a sensor system uses one or more HD NV diamonds with a high density of NV centers as described above. For example, the sensor system may use a single, single-crystal diamond with a high density of NV centers, or may use a powder or granule of nanodiamonds or diamonds with NV centers in a transparent material, these examples representing extreme cases of a wide range of examples between these extremes. We refer here to the as yet unpublished international patent application PCT DE 2020 100 430. Also, the NV centers can be used as single, isolated NV centers or used in such high density that two or preferably more NV centers couple together and collective effects become possible. The use of HD NV diamonds of high NV center density is preferred here. Alternatively, such a sensor system may comprise one or more crystals of other material having a high density of suitable alternative paramagnetic centers. For example, the sensor system may use a single, single crystal having a high density of paramagnetic centers (NV1) or use a granule or powder of, for example, nanocrystals or crystals having a high density of paramagnetic centers (NV1) in a transparent material, these examples again representing the two extreme cases of said wide range of examples.

[0172] As an alternative method, in addition to pumping the paramagnetic center or centers (NV1) with pump radiation (LB) from a pump radiation source (PL1), a sensor element and/or a local portion of the sensor element having the paramagnetic center or centers (NV1) is simultaneously irradiated with microwaves to selectively drive the spin transition. It is conceivable, in the case of a plurality of paramagnetic centers (NV1) within the sensor element, to irradiate a single paramagnetic center (NV1) or only a first subset of the paramagnetic centers (NV1) with the pump radiation (LB) and not to irradiate at least one paramagnetic center (NV1) of the paramagnetic centers of the sensor element or a second subset of the paramagnetic centers (NV1) of the sensor element with pump radiation (LB). By this, the fluorescence radiation (FL) then originates only from the paramagnetic centers (NV1) irradiated with pump radiation (LB). Since the areas of the sensor element that are irradiated with pump radiation (LB) and the areas of the sensor element that are not irradiated with pump radiation (LB) are known, a spatial resolution of the determination of the value of the physical parameters whose value is to be determined is thus achieved. The frequency of the superimposed microwave radiation and the strength of the magnetic flux density B to be measured can thus be correlated with local resolution. This can also be done in the same way for the determination of measured values of other physical quantities influencing the paramagnetic center (NV1) or the paramagnetic centers (NV1) or the group or groups (NVC) of paramagnetic centers (NV1), such as, for example, pressure P, temperature ϑ, acceleration a, gravitational field strength g, rotational speed ω and intensity of irradiation with ionizing radiation and their time integrals and derivatives. As a measurand for the magnetic flux density B and/or that of the electric flux density D and/or other the paramagnetic center(s) (NV1) or the group or groups (NVC) of paramagnetic centers (NV1) influencing physical values, such as i.e. pressure P, temperature ϑ, acceleration a, gravitational field strength g, rotational speed wand intensity of the irradiation with ionising radiation and their time integrals and derivatives, the changes in the intensity (I_fl) of the fluorescence radiation (FL) of the paramagnetic center (NV1) or of the paramagnetic centers (NV1) or of the group or groups (NVC) of paramagnetic centers (NV1), are in turn preferably used or the amount of generated and extracted photoelectrons of the paramagnetic center (NV1) or the paramagnetic centers (NV1) or the group or groups (NVC) of paramagnetic centers (NV1), or both is used. Although in this paper the intensity (I_fl) of the fluorescence radiation (FL) is generally taken as the basis of the measured value, in principle an extraction and detection of the photoelectrons in the form of a photocurrent of the photoelectrons of the paramagnetic center (NV1) or the paramagnetic centers (NV1) or the group or groups (NVC) of paramagnetic centers (NV1) and the use of my of these photoelectrons as the basis for the determination of the measured value directly from the sensor element is always included in the description and claiming.

[0173] The performance of a quantum mechanical sensor system can be massively limited by an unfavourable housing. In particular, for example, a housing with ferromagnetic subcomponents can cause distortions or shielding of magnetic fields and thus limit the usefulness of the sensor system. Also, an unfavorable housing can decisively increase the production costs of such a sensor device.

[0174] The proposal therefore further comprises a particularly suitable housing for the low-cost production of sensor systems with a paramagnetic center (NV1) in the material of a sensor element and/or in the material of a quantum technological device element which is part of the sensor system and/or quantum technological system. The proposed housing, which has already been processed to form the sensor system, typically comprises such a sensor system with a paramagnetic center (NV1) after the housing has been opened. Preferably, it is a sensor system as described above with one or more HD NV diamonds with a high density of NV centers as described above as the sensor element.

[0175] The proposed package may further comprise first means as first optical functional elements, for example a reflector (RE), for directing the pump radiation (LB) of the pump radiation source (PL1) to the paramagnetic center (NV1) and thus optically coupling the pump radiation source (PL1), for example an LED, to the paramagnetic center (NV1). As explained above, first optical functional elements such as optical waveguides, reflectors, lenses, prisms, open air gaps, vacuum gaps, apertures, mirrors, beam parts, gratings, etc. may be used for the optical coupling, some of which may also be manufactured as housing parts. Preferred is the use of the housing cover (DE) for this purpose.

[0176] The proposed package may further comprise second means as second optical functional elements, for example a reflector (RE), for directing the fluorescent radiation (FL) of the one or more paramagnetic centers (NV1) to the radiation receiver (PD) and thus coupling the radiation receiver (PD), for example a photodiode, to the one or more paramagnetic centers (NV1). As explained above, second optical functional elements such as optical waveguides, reflectors, lenses, prisms, open air gaps, vacuum gaps, apertures, mirrors, beam parts, gratings, etc. may be used for the optical coupling, some of which may also be manufactured as housing parts. Preferably, the housing cover (DE) is also used for this purpose.

[0177] Preferably, an optical filter (F1) is located in this beam path between the parametric center or centers (NV1) and the radiation receiver (PD), which does not attenuate or only insignificantly attenuates the fluorescence radiation (FL) with respect to the application and thus transmits it, and which sufficiently attenuates the pump radiation (LB) with respect to the application and thus absorbs or reflects it and precisely does not transmit it. As a result, only the radiation, the fluorescence radiation (FL), with fluorescence radiation wavelength (λfl) can reach the radiation receiver (PD) and radiation with pump radiation wavelength (λ_pmp), the pump radiation (LB), cannot reach the radiation receiver (PD).

[0178] Preferably but not necessarily, these immediately before mentioned first means and/or second means are part of the housing itself. For example, the inner side of a cover (DE) of the housing can be formed as a mirroring reflector (RE) for directing the pump radiation (LB) and/or the fluorescence radiation (FL), for example by means of polishing and/or single-layer or multilayer optionally also structured coating. Better is a mirroring of surfaces of the housing, especially of parts of the housing cover (DE). Especially favourable and preferred is an additional focussing curvature of the inner side of the cover (DE).

[0179] An exemplary example of such a sensor system is described, for example, in German patent application DE 10 2018 127 394 A1, the publication date of which is after the claimed priority dates of this application document. However, the sensor system can also be explicitly embodied in a different way than described in the German patent application DE 10 2018 127 394 A1. The proposed housing is therefore, in general, a proposed low-cost housing for sensor systems comprising a paramagnetic center (NV1) as a functional element, without the specific measurement task playing a role here with respect to the housing. Importantly, the physical parameter to be sensed can reach the paramagnetic center(s) (NV) or group(s) (NVC) of paramagnetic centers (NV1) within the housing. This should be taken into account when selecting the materials of the enclosure and its construction. For example, if a magnetic flux density B is to be detected, it is preferable to make the housing from non-magnetic materials, firstly so as not to distort or modify the physical quantity to be detected and secondly so as not to cause a shielding effect. The same applies to other materials used, such as fastening means and materials.

[0180] Preferably, all subdevices of the housing and of the sensor system are designed to be non-ferromagnetic in order to minimize the influence of the paramagnetic center (NV1). By “non-ferromagnetic” is meant herein a permeability number μ_r lower than 100. Preferably, all components of the housing and the sensor system and/or the quantum technological system are diamagnetic, by which is understood herein a permeability number of the materials with μ_r<1 (typically would be 1-7*10⁻⁶ . . . 1-2*10⁻⁴), and/or paramagnetic, by which is understood herein a permeability number of the materials with μ_r>1 (typically would be 1+1*10⁻⁸ . . . 1+4*10⁻⁴). However, for the purposes of the present disclosure, materials having a permeability number μ_r<100 are also considered to be non-ferromagnetic. Thus, paramagnetic and diamagnetic substances are not ferromagnetic for the purposes of the present disclosure. Most preferably, all lead frame surfaces (LF1 to LF6) of the housing are made non-ferromagnetic.

[0181] Thus, in the housing that houses the paramagnetic center (NV1) in the material of a sensor element, all sub-devices of the sensor system are preferably non-ferromagnetic.

[0182] If necessary, it may be useful to provide a magnetic shield (MAS) of soft magnetic material between the radiation receiver (PD1) and the evaluation circuit, i.e., the integrated circuit (IC), when using an integrated circuit (IC). Such shielding (MAS) may also be provided to magnetically shield the paramagnetic center (NV1) or centers (NV1) or the group or groups of paramagnetic centers (NV1) from the integrated circuit (IC) and/or other potentially current-carrying device parts. Such a package with such shielding (MAS) is considered to be made of non-ferromagnetic materials for the purposes of this disclosure, as it exhibits this property after the shielding (MAS) is removed.

[0183] The housing with the functionalized paramagnetic center (NV1) in the material of a sensor element is thus preferably designed in such a way that all sub-devices of the sensor system including the housing, with the exception of a soft magnetic shield (MAS), are made of a soft magnetic material and/or, with the exception of parts of a magnetic circuit, are not made of a ferromagnetic material, but preferably of a paramagnetic and/or diamagnetic material. For the purposes of the present disclosure, a soft magnetic material is understood to be, in accordance with DIN EN 60404-1:2017-08, a material with a coercive field strength<=1 000 A/m. Even smaller coercive field strengths are preferred.

[0184] For simplicity, the term sensing element is used herein as a synonym for a sensing element and/or a quantum technology device element.

[0185] A very cost-effective method of manufacturing a sensor system is proposed herein, comprising the following steps, even in a different order:

• • [0186] Providing an open cavity housing with connections and with a cavity (CAV) having a mounting opening (MO) for insertion of system components;
  • [0187] Insert the pump radiation source (PL1) into the cavity (CAV) of the open cavity housing through the mounting hole (MO);
  • [0188] Inserting an integrated circuit (IC) comprising the evaluation circuit into the cavity (CAV) of the open cavity housing using the mounting opening (MO), wherein the integrated circuit (IC) preferably comprises the radiation receiver (PD1);
  • [0189] Unless the integrated circuit (IC) comprises the radiation receiver (PD1), the method also prefers inserting the radiation receiver (PD1) into the cavity (CAV) of the open cavity housing through the mounting opening (MO) in a typically separate step;
  • [0190] Electrical connection of integrated circuit (IC), terminals of the open cavity housing, pump radiation source (PL1) and possibly separate radiation receiver (PD1), in particular by means of bond connections (BD1 to BD4);
  • [0191] Incorporating a sensor element with one or more paramagnetic centers (NV1) or one or more groups (NVC) of paramagnetic centers (NV1) in the material of the sensor element, for example a sensor element with one or more diamonds with one or more NV centers and/or one or more groups of NV centers, preferably one or more HD-NV diamonds with an at least locally high density of NV centers, via the mounting opening (MO) into the cavity (CAV) of the open cavity housing;
  • [0192] fixing the sensor element by means of an attachment and fixing means (Ge), preferably the attachment and fixing means (GE) being shaped and/or selected and/or mounted in such a way that the pumping radiation (LB) can reach the paramagnetic center (NV1) or centers (NV1) or the group or groups (NVC) of paramagnetic centers (NV1) and that the fluorescence radiation (FL) of the paramagnetic center (NV1) or paramagnetic centers (NV1) or group or groups (NVC) of paramagnetic centers (NV1) can reach the radiation receiver (PD1);
  • [0193] producing first means for directing the pump radiation (LB) and/or second means for directing the fluorescence radiation (FL), these means preferably, but not necessarily, being part of the housing, and, if appropriate, fixing the first means and/or the second means to the housing or housing parts if the respective means is not part of the housing or a housing part of the housing and/or can be produced as such;
  • [0194] Closing the housing, in particular the mounting opening (MO), with a cover (DE), which is considered a housing part in this writing.

[0195] A first method is presented for testing a housing having a sensor system at least partially fabricated in the housing, in accordance with the foregoing and subsequent proposals. The test method is preferably performed before closing the mounting opening (MO). The mounting opening (MO) is used here for supplying the test signals. In particular, the idea is to use the mounting opening (MO) for feeding a well-controlled, preferably calibrated and adjustable test pump radiation (TLB) corresponding to pump radiation (LB) and extracting a well-controlled, preferably calibrated and adjustable test radiation (TFL) corresponding to fluorescence radiation (FL) out of the housing and to measure the electrical and/or physical response of device components of the sensor system in the housing. For example, such a test method comprises the steps of:

• • [0196] Irradiation of the open housing through the mounting opening (MO) with pump radiation (LB);
  • [0197] Measurement of the fluorescence radiation (FL) emitted by the housing via the open mounting opening (MO), wherein this measurement can be carried out by the sensor system itself and/or a measuring device outside the housing preferably via the mounting opening (MO) or another measurement path. Preferably, the intensity (I_fl) of the fluorescence radiation (FL) is detected as a function of the intensity (I_pmp) of the pump radiation (LB) and/or as a function of the value of one or more physical parameters, which may be, for example, the value of the magnetic flux density B and/or the temperature and/or a pressure, etc;
  • [0198] Evaluating the measured value or values of the fluorescence radiation (FL), in particular preferably the measured value of the intensity (I_fl) of the fluorescence radiation (FL), by comparing the measured value or values of the fluorescence radiation (FL) at one or more measurement parameter configurations, each corresponding to one or more predetermined intensity values (I_pmp) of the pump radiation (LB) and/or one or more predetermined values of the influencing physical parameters or a combination thereof, with at least one threshold value associated with the respective measurement parameter configuration. Preferably, the housing is discarded or reworked with the sensor system if this comparison does not correspond to an expected value.

[0199] A second method is further proposed for testing a housing comprising a sensor system according to the preceding proposal. The second proposed test method is also preferably performed before closing the mounting opening (MO). The basic idea is the same as for the first test procedure presented previously. This second test procedure comprises the steps of:

• • [0200] Operate pump radiation source (PL1) in the sensor system inside the housing with an open housing with open mounting hole (MO) without housing cover (DE);
  • [0201] Measurement of the pump radiation (LB) typically emitted via the mounting opening (MO) of the open housing through the paramagnetic center or centers (NV1) by the pump radiation source (PL1), wherein, for example, one or more measured values for the intensity (I_pmp) and/or, if applicable, the intensity distribution of the pump radiation (LB) are determined;
  • [0202] Evaluating the measured value or values of the pump radiation (LB), in particular preferably the measured value of the intensity (I_pmp) of the pump radiation (LB), by comparing the measured value or values of the pump radiation (LB) at one or more measurement parameter configurations, each corresponding to one or more predetermined values of the physical parameters (e.g. operating voltage or temperature) influencing the pump radiation source (PL1) or a combination thereof, with at least one threshold value associated with the respective measurement parameter configuration. Preferably, the housing with the sensor system and/or the sensor system is discarded or reworked if this comparison does not correspond to an expected value.

[0203] A third proposed method for testing a housing comprising a sensor system according to the preceding proposal is proposed. The third proposed test method is also preferably performed before closing the mounting opening (MO) of the housing. The basic idea is the same as for the first and second test procedures presented previously. This third test procedure comprises the steps of:

• • [0204] Operate pump radiation source (PL1) in the sensor system with an open housing with an open mounting hole (MO);
  • [0205] Direction of the pump radiation (LB) emitted by the pump radiation source (PL1) by means of optical functional components, for example a test mirror, to the radiation receiver (PD1);
  • [0206] Measurement of the fluorescence radiation (FL) emitted by the housing preferably via the mounting opening (MO), wherein this measurement can be carried out by the sensor system itself and/or a measuring device outside the housing preferably via the mounting opening (MO) or another measurement path. Preferably, the intensity (I_fl) of the fluorescence radiation (FL) is detected as a function of the intensity (I_pmp) of the pump radiation (LB) and/or as a function of the value of one or more physical parameters, which may be, for example, the value of the magnetic flux density B and/or the temperature and/or a pressure, etc;
  • [0207] Evaluating the measured value or values of the fluorescence radiation (FL), in particular preferably the measured value of the intensity (I_fl) of the fluorescence radiation (FL), by comparing the measured value or values of the fluorescence radiation (FL) at one or more measurement parameter configurations, each corresponding to one or more predetermined intensity values (I_pmp) of the pump radiation (LB) and/or one or more predetermined values of the influencing physical parameters or a combination thereof, with at least one threshold value associated with the respective measurement parameter configuration. Preferably, the housing with the sensor system and/or the sensor system is discarded or reworked if this comparison does not correspond to an expected value.

[0208] The first method, the second method and the third method may be combined.

[0209] Two things are now proposed for the realization of a current sensor, both of which should preferably be fulfilled in addition to that described above:

[0210] As a first step, a sensor system and/or quantum technological system—also referred to in this paper only simplified as sensor system—is proposed, in which the sensor system is accommodated in a housing and in which the sensor system comprises one or more paramagnetic centers (NV1) or one or more groups (NVC) of paramagnetic centers (NV1) in the material of a sensor element and/or quantum technological device element which is part of the sensor system. The sensor system of the current sensor comprises said pump radiation source (PL1) for pump radiation (LB), which is preferably an LED. As described above, the pump radiation (LB) causes the paramagnetic center or centers (NV1) or the group or groups (NVC) of paramagnetic centers (NV1) to emit fluorescence radiation (FL). Furthermore, the components of the housing and/or the sensor system described further above may also be present. In contrast to the above description, the housing now additionally comprises at least one line through which the electric current to be detected and measured flows. Preferably, this line is galvanically isolated from the other device parts of the sensor system. The only exception may be the sensor element with the paramagnetic center (NV1). If an NV center in diamond is used, the diamond may be in direct electrical high resistance contact and mechanical contact with the conductor and one or more NV centers of the diamond may be optically coupled to the rest of the sensor system. Here, it can be exploited that diamond is generally electrically insulating. The magnetic field of the conduction in the form of the generated magnetic flux density B at the location of the paramagnetic center(s) (NV1) or group(s) (NVC) of the paramagnetic centers (NV1) influences the intensity (I_fl) of the fluorescence radiation (FL) of the paramagnetic center(s) (NV1) or of the paramagnetic centers or of the group or groups (NVC) of the paramagnetic centers (NV1) in the material of a sensor element and/or of the quantum technological device element. In this case, it can then be exploited that the magnetic flux density B around a current-carrying conductor decreases with 1/r, where r is the distance of the paramagnetic center (NV1) or the plurality of paramagnetic centers (NV1) or the group or groups (NVC) of paramagnetic centers (NV1) from the current-carrying conductor (LTG, LH, LV). Preferably, the paramagnetic center(s) (NV1) or the group(s) (NVC) of paramagnetic centers (NV1) are located at a first distance (r) of less than 1 μm, preferably less than 500 nm, preferably less than 200 nm, preferably less than 100 nm, preferably less than 50 nm, preferably less than 20 nm from the exemplary horizontal conductor (LH). In the elaboration of the disclosure, it has been considered that the line (LH) is particularly preferably less than 50 nm away from the paramagnetic center(s) (NV1) or the group(s) (NVC) of paramagnetic centers (NV1). Due to this small distance (r), significant magnetic flux densities B at the location of the paramagnetic center(s) (NV1) or the group(s) (NVC) of paramagnetic centers (NV1) can already be achieved with electrical currents (IH) in the line (LH, LV, LTG) which are very small in magnitude and which influence the fluorescence radiation (FL) of the paramagnetic center(s) (NV1) or group(s) (NVC) of paramagnetic centers (NV1), if necessary, in parallel in time with other possibly relevant physical parameters. This is particularly advantageous if a plurality of lines (LH) is fabricated on the substrate (D), to each of which a paramagnetic center (NV1) from a total set of paramagnetic centers (NV1) or a group (NVC) of paramagnetic centers (NV1) from a total set of a plurality of groups (NVC) of paramagnetic centers (NV1) is assigned. Advantageously, by adjusting the magnetic flux density B by means of different electric currents in the different lines (LH), the contrast (KT) of the respective paramagnetic centers (NV1) associated with the respective lines (LH) or of the respective groups (NVC) of paramagnetic centers (NV1) associated with the respective lines (LH) can then be adjusted differently by the resulting different respective magnetic flux density B at the location of the respective paramagnetic center (NV1) or at the location of the respective group (NVC) of paramagnetic centers. Thus, a method and an apparatus are disclosed herein for differently adjusting the contrast (KT) of different paramagnetic centers (NV1) and/or different groups (NVC) of paramagnetic centers (NV1). Similarly, the plurality of lines (LH) may be provided with an electric potential different from each other with respect to the electric potential of the substrate (D). By such an electric potential of a line (LH), the Fermi level at the location of a paramagnetic center (NV1) associated with this line (LH) and located in the vicinity of the line (LH) or at the location of a group (NVC) of paramagnetic centers (NV1) associated with said line (LH) and located in the vicinity of said line (LH), wherein proximity here refers to the above values for the distance (r) between a line (LH) and the paramagnetic center (NV1) associated with said line or the group (NVC) of paramagnetic centers (NV1) associated with said line (LH). Through this, the charge state of the plurality of paramagnetic centers (NV1) in the vicinity of the plurality of lines (LH) can be set differently in each case by selecting and setting differently the electric potentials of the lines (LH). In the case of NV centers as paramagnetic centers (NV1), in this way, some NV centers can be forced into the fluorescent NV⁻ state and thus light up, while other NV centers can be forced into other states and thus not fluoresce and thus not light up. Since the distance between the lines (LH) and also between the paramagnetic centers (NV1) located in their vicinity is smaller than the pump radiation wavelength (λ_pmp) and smaller than the fluorescence radiation wavelength (λ_fl), a sensor system can be produced in this way whose spatial resolution is smaller than that without such a selection structure. For example, individual paramagnetic centers (NV1) or individual groups (NVC) of paramagnetic centers (NV1) can be activated one after the other by applying a suitable potential to the line (LH) associated with this paramagnetic center (NV1) or this group (NVC) of paramagnetic centers (NV1), i.e. brought into a fluorescent state, with all the other or at least most of the other paramagnetic centers (NV1) or other groups (NVC) of paramagnetic centers (NV1) preferably being simultaneously deactivated, i.e. brought into a non-fluorescent state. In the case of NV centers as paramagnetic centers (NV1), the line associated with an NV center is preferably positively charged with respect to the substrate (D) for the activation of the NV center, so that the NV center located in the vicinity is brought into the negatively charged, fluorescent NV⁻⁻ state, and preferably negatively charged with respect to the substrate (D) for deactivation of the NV center, so that the nearby NV center leaves the negatively charged fluorescent NV⁻⁻ state and thus no longer fluoresces. This method can also be used to impose a modulation on the intensity (I_fl) of the fluorescent radiation (FL). The modulations may be specific to the line (LH) in the case of multiple lines and multiple paramagnetic centers (NV1) respectively associated with these lines (LH), so that in the frequency spectrum of the modulation of the intensity (I_fl) of the fluorescent radiation (FL) these different modulations are reflected. For example, it is conceivable to monofrequency the modulations of the different lines and to select a different line-specific modulation frequency for each line (LH). Thus, the intensity (I_fl) of the fluorescence radiation (FL) of the paramagnetic centers (NV1) or of the groups (NVC) of paramagnetic centers is modulated in accordance with the line-specific modulation frequency corresponding to the line (LH) which is close to them in each case, so that the spectrum of the intensity (I_fl) of the fluorescence radiation which reaches the radiation receiver (PD) and thus the spectrum of the receiver output signal (S0) has a superposition of these modulation frequencies which can be separated again by optimum filters, synchronous demodulators, bandpass filters or the like if the spacings of these modulation frequencies in the frequency spectrum are suitably selected. In this way, a spatial resolution below the fluorescence radiation wavelength (λ_fl) and below the pump radiation wavelength (λ_pmp) is possible.

[0211] The sensor system determines, for example, a value for the intensity (I_fl) of the fluorescence radiation (FL) by means of said radiation receiver (PD1) and, for example, said integrated circuit (IC) by means of the evaluation circuit, and provides and/or outputs this value for the intensity (I_fl) of the fluorescence radiation (FL) in digital and/or analog form, for example as a sensor output signal (out). Since the intensity (I_fl) of the fluorescence radiation (FL) of a paramagnetic center (NV1) depends on the magnetic flux density B at the location of the paramagnetic center (NV1), a value for the intensity (I_fl) of the fluorescence radiation (FL) and thus the value of the sensor output signal (out) is a possible measure of the magnetic flux density B at the location of the paramagnetic center and thus of the current value of the electric current through the conductor which causes this magnetic flux density B. Thus, it is possible to construct a current measuring system with the aid of a paramagnetic center (NV1) or several paramagnetic centers or a group (NVC) of paramagnetic centers (NV1) or several groups of paramagnetic centers (NV1) without the aid of microwaves.

[0212] This paper thus describes a sensor system with one or more paramagnetic centers (NV1) or one or more groups (NVC) of paramagnetic centers (NV1) in a substrate (D), hereinafter also referred to in simplified form as paramagnetic centers (NV1), the sensor system comprising first means (G, PL1, F1, PD, M1, TP) for exciting and detecting and evaluating the fluorescence radiation (FL) of these paramagnetic centers (NV1), and the sensor system generating and/or providing a measured value by means of the first means (G, PL1, F1, PD, M1, TP) as a function of the fluorescence radiation (FL) of these paramagnetic centers (NV1). The sensor system preferably comprises an electrical conductor (LH, LV, LTG). The electrical conductor (LH, LV, LTG) is preferably mechanically connected to the substrate (D) having the paramagnetic centers (D). The electrical conductor (LH, LV, LTG) preferably has an electrical current (IH, IV) flowing through it. The said electric current (IH, IV) now generates a magnetic flux B which affects the fluorescence radiation (FL) of these paramagnetic centers (NV1). Is the shortest distance (r) between the center of gravity of the paramagnetic centers (NV1) and the conductor (LH, LV, LTG) shorter than 1 μm, better less than 500 nm, better less than 200 nm, better less than 100 nm, better less than 50 nm, better less than 20 nm or is the shortest distance (r) between a paramagnetic center (NV1) of the paramagnetic centers (NV1) and the conductor (LH, LV, LTG) is shorter than 1 μm, preferably less than 500 nm, preferably less than 200 nm, preferably less than 100 nm, preferably less than 50 nm, preferably less than 20 nm, the magnetic flux density B acting on the paramagnetic centers (NV1) is very large, which increases the sensitivity of the current measurement.

[0213] As already indicated in the explanation of the basic structure of the sensor system, a control and evaluation unit (LIV) is required to operate the sensor system. This control and evaluation unit (LIV) is preferably an integrated circuit. Only parts of the control and evaluation unit (LIV) may also be part of an integrated circuit (IC). In addition to the control and evaluation unit (LIV), the integrated circuit (IC) can comprise further functional elements, such as the radiation receiver (PD), the pump radiation source (PL1)—for example in the form of a pump radiation (LB) radiating center (PZ)—, the compensation radiation source (PLK), the first filter (F1)—for example as a functional element of diffractive or digital optics/photonics—, the paramagnetic center (NV1)—for example as a G-center in silicon or V-center in SiC—, the transmission paths—for example as micro-integrated optical waveguides, a computer system (μC) and optionally further control devices, data bus interfaces, etc. Reference is made here to the application PCT/DE 2020/100 430, which is still unpublished at the time of this application.

[0214] Therefore, an integrated circuit (IC) for use with one or more paramagnetic centers (NV1) or a group or groups (NVC) of paramagnetic centers (NV1) in the material of a sensor element is also proposed herein. The integrated circuit (IC) preferably comprises a driver for driving a pump radiation source (PL1), preferably a radiation receiver (PD1), for detecting the fluorescence radiation (FL) of the one or more paramagnetic centers (NV1) and/or the group or groups (NVC) of paramagnetic centers (NV1), an evaluation circuit for generating a sensor output signal (out) which depends on the fluorescence radiation (FL) of the paramagnetic center (NV1) in the material of a sensor element, and preferably on the intensity (I_fl) of the fluorescence radiation (FL). Here, the sensor element is preferably a diamond crystal. The paramagnetic center(s) (NV1) or group(s) (NVC) of paramagnetic centers (NV1) are preferably an NV center(s) or one or more groups of NV centers in the diamond crystal or in a plurality of diamond crystals. The radiation receiver (PD) need not necessarily be part of the integrated circuit (IC). It may be located outside the integrated circuit.

[0215] Preferably, the sensor system and/or the housing of the sensor system comprises a magnetic circuit or parts of such a magnetic circuit, hereinafter also referred to as magnetic circuit elements.

[0216] For example, it may be useful to change the magnetic flux B to be measured in the vicinity of the paramagnetic center (NV1) by additional preferably soft magnetic circuit elements in order to change the sensitivity field of the sensor system and/or the quantum technological device with respect to external magnetic fields. In particular, it is possible to deform the sensitivity field so that preferred directions and/or a direction-dependent sensitivity can be obtained. For example, it is possible to achieve such a deformation by means of a means for deforming the magnetic field. Such a means for deforming the magnetic field can be, for example, ferromagnetic device parts which are brought into the vicinity of the paramagnetic centers (NV1) and/or the vicinity of groups (NVC) of such paramagnetic centers (NV1) and then deform the field lines of the magnetic flux B there. For example, it is conceivable to make a slot in a sheet of ferromagnetic material and to place the paramagnetic centers (NV1) or groups of paramagnetic centers (NV1) in the slot. The magnetic flux density B, when arranged perpendicular to the surface normal of the ferromagnetic sheet, is concentrated in the sheet and reduced in the slot so that the intensity (I_fl) of the fluorescence radiation (FL) of the paramagnetic centers (NV1) is little affected by the magnitude of the magnetic flux B. The magnetic flux density B, when arranged parallel to the surface normal of the ferromagnetic sheet and perpendicular to the direction of the slit, is concentrated in the sheet, and thus, at these orientations, but also concentrated in the slit, so that the intensity (I_fl) of the fluorescence radiation (FL) of the paramagnetic centers (NV1) is now very strongly influenced by the magnitude of the magnetic flux B. As a result, the dependence of the intensity (I_fl) of the fluorescence radiation (FL) on the magnitude of the magnetic flux density B now behaves anisotropically and thus then depends on the spatial direction.

[0217] Thus, a device for measuring a magnetic flux density B is described here which, firstly, comprises at least one of the other sensor systems described in this paper, which determine a value for the magnetic flux density b by means of detecting and evaluating parameters of the fluorescence radiation (FL) of one or more paramagnetic centers (NV1) and/or of one or more groups (NVC) of paramagnetic centers (NV1), and which, secondly, additionally comprises a ferromagnetic functional element which deforms the field profile of the magnetic flux density B in such a way that the measured value, which is determined by the device for measuring a magnetic flux density B with the aid of the said other sensor systems described in this paper as a function of the magnetic flux density B of this magnetic field deformed by means of the said ferromagnetic function element, depends on the direction of the flux density B acting from outside on the device for measuring a magnetic flux density B.

[0218] Dicke receivers are known from radio astronomy. More information can be found on the Internet under the keyword “Dicke receiver”. At this point, reference is made to the paper U. Klein, “Radio astronomy: tools, applications and impacts; Course astro 841” Argelander Institute for Astronomy Bonn, 2011 edition. At the time of the international application, the publication can be found at the link:

• • [0219] https://hera.ph1.uni-koeln.de/ftpspace/simonr/Pablo/Radioastronomy.pdf

[0220] Chapter 6.4.2 on page 82 ff. describes the basic construction of a Dicke receiver.

[0221] Such a Dicke amplifier is used for the detection of static, constant sources in highly noisy environments. The eliminable noise is the thermal 1/f noise in the measurement channel. In order to detect the source whose amplitude is below the noise level; switching is performed between the noisy input signal of the antenna and the noise signal of an equivalent noise source of the same temperature as the noise background of the received signal. This is done at a sufficiently high frequency. If, for example, the static signal of a stellar object is part of the received signal, this object signal can be raised above the noise background by multiplying the resulting signal with the switching signal.

[0222] This principle is now applied to the measurement of the paramagnetic centers (NV1), i.e., preferably the NV centers. A compensating radiation source (PLK), which is preferably designed as a light-emitting diode, called LED for short, or as a laser, serves as a comparative noise source. If properly designed, the noise level is also lowered here compared to the signal level. The compensation radiation (KS) of the compensation radiation source (PLK) has a compensation radiation wavelength (λ_ks).

[0223] According to the disclosure, it was thus realized that the fundamental problem of radio astronomy to detect a very small signal in front of a thermally noisy noise background is the same problem that occurs in quantum sensors. Irradiation with pump radiation (LB) leads to a massive reduction of the spin temperature of a paramagnetic center (NV1). In the present disclosure, sensor elements with a high density of paramagnetic centers (NV1), for example comprising HD-NV diamonds, are preferably used. This high density and low spin temperature make the noise of the fluorescence radiation (FL) of the sensing element itself practically disappear. This is not the case with other systems using isolated paramagnetic centers (NV1), e.g., single or few NV centers. Consequently, the system noise originates mainly from the pump radiation source (PL1), the radiation receiver (PD) or the first amplifier stages, which typically have the lowest signal-to-noise ratio. The noise of the pump radiation source (PL1) is thus imposed on the noise of the intensity (I_fl) of the fluorescence radiation (FL) of the paramagnetic center (NV1).

[0224] Unlike radio astronomy, fluorescence radiation (FL) can be modulated. Thus, it does not require the Dicke switch of radio astronomy. In the course of the elaboration of the disclosure, it was recognized that the system is preferably constructed in such a way that a pump radiation source (PL1) emits the pump radiation (LB), which is then directed to the sensor element with the paramagnetic center (NV1) or with a plurality of paramagnetic centers (NV1) with possibly at least locally high density of paramagnetic centers (NV1). A locally high density of paramagnetic centers may be achieved in a group (NVC) of paramagnetic centers having an extension d within the sensor element or within a substrate (D) within the sensor element. The paramagnetic center (NV1) or centers (Nv1) or the group or groups (NVC) of paramagnetic centers (NV1) then emit the fluorescence radiation (FL) as a function of the intensity (I_pmp) of the pump radiation (LB) and as a function of further physical parameters, for example the actual value of the magnetic flux density B or the electric flux density D or the pressure P or the temperature ϑ or the acceleration a or the gravitational field strength g or the rotational speed ω or time integrals or derivatives of these quantities or frequencies of the fluctuation of these quantities at the location of the respective paramagnetic center (NV1). For example, since the pump radiation (LB) is noisy in the case where a semiconductor laser is used as the pump radiation source (PL1) as a result of the relatively high temperature of the light-emitting PN junction in the laser of the pump radiation source (PL1), this modulation of the pump radiation (LB) with a pump noise signal component of the modulation of the intensity (I_pmp) of the pump radiation (LB) is also found as a fluorescence noise signal component of the fluorescence radiation (FL). Preferably, the temperature of the pump radiation source (PL1) is detected, for example, by a thermal sensor. A pump radiation source controller then preferably readjusts one of the drive parameters of the pump radiation source (PL1). The actual quantity of the pump radiation source controller is the temperature value determined by the thermal sensor for the temperature of the pump radiation source (PL1). The desired quantity is usually a temperature reference value. Preferably, the controller is a PID controller. The possible controllable drive parameters of the driver stage of the pump radiation source (PL1) are the pulse height, the pulse repetition frequency, and the pulse duration. Thus, it is apparent that it is convenient for the pump radiation source controller to intervene, if necessary, in the signal generator (G) which generates some of these variables. It is also conceivable to provide a heater or a cooling device and a heater, and to readjust the heater and/or the cooling so that the temperature of the pump radiation source remains constant to within a few mK.

[0225] It is now the idea according to the disclosure, as in a Dicke receiver, to compare the noisy signal of the intensity (I_fl) of the fluorescence radiation (FL) with a reference noise source by means of the same, better the identical subsequent signal path. The reference noise source is preferably made equal to the pump radiation source (PL1). In the following, this reference noise source is referred to as compensation radiation source (PLK).

[0226] If the compensation radiation source (PLK) is constructed in the same way as the pump radiation source (PL1), it will make noise approximately in the same way at the same thermal and electrical operating point. However, compensation with a differently constructed compensating radiation source (PLK) is explicitly less preferred also possible. Preferably, the compensation radiation source (PLK) is selected such that the compensation radiation wavelength (λ_ks) of the compensation radiation (KS) of the compensation radiation source (PLK) is equal or similar to the pump radiation wavelength (λ_pmp) of the pump radiation (LB) of the pump radiation source (PL1). For example, if the pump radiation source (PL1) is green, as in the case of NV centers as paramagnetic centers (NV1), the compensation radiation source (PLK) is preferably also green. Alternatively, but not preferably, the compensation radiation wavelength (λ_ks) is selected so as not to be suitable for exciting the paramagnetic center(s) (NV1) in question or the group(s) (NVC) of paramagnetic centers (NV1). Thus, for this purpose, the compensating radiation wavelength (λ_ks) may be, for example, longer than the fluorescence radiation wavelength (λ_fl)—e.g., of 637 nm for NV centers—in order to reliably prevent such excitation of the fluorescence of the paramagnetic center (NV1) by compensating radiation (KS). In reality, optical attenuation of the compensating radiation (KS) prior to impingement on the radiation receiver (PD) will be necessary to match the intensity of the portion of the compensating radiation (KS) impinging on the radiation receiver (PD) to the intensity, of the portion of the fluorescence radiation (FL) hitting the radiation receiver (PD) for a selected optical operating point with respect to the intensity of the portion of the operating point intensity of the fluorescence radiation (FL) hitting the radiation receiver (PD) at this operating point. The pump radiation wavelength (λ_pmp) is usually chosen to be smaller than the fluorescence radiation wavelength (λ_fl)—e.g., 637 nm for NV centers. This is done, for example, by the pump radiation source (PL1) of the pump radiation (LB) preferably being a green, blue, or ultraviolet LED or a corresponding laser. Preferably, the pump radiation wavelength (λ_pmp) is 532 nm as described in the case of NV centers as paramagnetic centers. A laser having a pump radiation wavelength (λ_pmp) of 520 nm as a pump radiation source (PL1) is also described herein. By this, a paramagnetic center (NV1), which is preferably a NV center in diamond, can be excited to a higher energy level. The absorption characteristics of the paramagnetic center(s) (NV1) or group(s) (NVC) of paramagnetic centers (NV1) must be considered.

[0227] For example, if we assume that the one or more paramagnetic centers (NV1) are NV centers in diamond, two green lasers with, for example, preferably 532 nm or 520 nm pump radiation wavelength (λ_pmp) may be used. A first laser is then used, for example, as a pump radiation source (PL1). For example, this pump radiation source (PL1) in the form of the first laser may also be a first laser diode of the company Osram of the type PLT5 520B with 520 nm pump radiation wavelength (λ_pmp), which is commercially available. A second laser is then used, for example, as a compensating radiation source (PLK). For example, this compensating radiation source (PLK) in the form of the second laser may also be a second laser diode from Osram of the type PLT5 520B with 520 nm pump radiation wavelength (λ_pmp), which is commercially available.

[0228] If only a portion of the light output of the first laser corresponding to the intensity (I_pmp) of the pump radiation (LB) is converted into intensity (I_fl) of the fluorescence radiation (FL), it is strongly recommended to reduce the luminous intensity (I_ks) of the compensation radiation (KS) of the compensation radiation source (PLK). This can be done electrically or, better, optically by means of an absorption filter, for example an aperture or a grey wedge.

[0229] In the radiation receiver (PL1), the compensation radiation (KS) and the fluorescence radiation (FL) are then superimposed in an approximately linear summation.

[0230] The Dicke switch for switching between the noisy signal and the reference noise source, which is switched over with a so-called chopper signal, is now implemented in such a way that instead the pump radiation source (PL1) is switched on and off with a transmission signal (S5) as chopper signal and the compensation radiation source (PLK) is switched on in a complementary manner with a compensation transmission signal (S7) complementary to the transmission signal (S5). In the simplest case, the compensation radiation source (PLK) is thus always switched on when the pump radiation source (PL1) is switched off and vice versa. Through this, as in the case of the Dicke receiver, switching is performed between the noisy fluorescence signal of the intensity (I_fl) of the fluorescence radiation (FL) and the reference noise signal in the form of the intensity (I_ks) of the compensation radiation (KS) of the compensation radiation source (PLK).

[0231] It is conceivable to use deviating radiation sources as compensating radiation sources (PLK). This can also have cost reasons. It is conceivable to use light-emitting diodes, hereinafter also referred to as LEDs, instead of lasers for the pump radiation source (PL1) and the compensation radiation source (PLK). It is conceivable that the compensation radiation source (PLK) has a center of gravity wavelength as the compensation radiation wavelength (λ_ks) in the spectrum of its radiation, which is not suitable for exciting the fluorescence radiation (FL) of the paramagnetic centers (NV1). For example, the compensating radiation source (PLK) may be an infrared LED. In the case of one or more NV centers as paramagnetic centers (NV1), the compensation radiation wavelength (λ_ks) is then selected to be in the infrared region. As a result, the compensating radiation (KS) cannot excite the fluorescence radiation (FL) of the NV center(s) or the group(s) (NVC) of NV centers and thus cannot generate fluorescence radiation (FL) of the NV center(s) or the group(s) (NVC) of NV centers.

[0232] The transmission signal (S5) is modulated. The instantaneous intensity (I_pmp) of the pump radiation (LB) emitted by the pump radiation source (PL1) typically depends on the value of the transmission signal (S5).

[0233] This can be described by the following equation I:

[0234] $i1=h{0}^{{ }_{}\prime }+{\mathrm{hRA}}^{{ }_{}\prime }+h1*s5w+h1*s5g+\mathrm{hRb}*s5w+\mathrm{hRb}*s5g$

[0235] i1 stands here for the instantaneous value of the intensity (I_pmp) of the pump radiation (LB) emitted into the first transmission path (I1) by the pump radiation source (PL1). hRa′ represents the noise of the pump radiation source (PL1) at the operating point, which is independent of the value of the transmission signal (S5) and thus independent of the value of the alternating component (S5w) of the transmission signal (S5) and independent of the value of the DC component (S5g) of the transmission signal (S5). hRb represents the noise of the pump radiation source (PL1), which is dependent on the value of the transmission signal (S5) and thus dependent on the value of the alternating component (S5w) of the transmission signal (S5) and dependent on the value of the DC component (S5g) of the transmission signal (S5). h0′ is an offset value for the value of the intensity (I) of the pump radiation (LB) emitted into the first transmission path (I1) by the pump radiation source (PL1), which intensity (I_pmp) is independent of the value of the transmission signal (S5) at the operating point and thus independent of the value of the alternating component (S5w) of the transmission signal (S5) and independent of the value of the direct component (S5g) of the transmission signal (S5). h1 is a proportionality factor for the value of the intensity (I_pmp) of the pump radiation (LB) emitted into the first transmission path (I1) by the pump radiation source (PL1), which is dependent at the operating point on the value of the transmission signal (S5) and thus dependent on the value of the alternating component (S5w) of the transmission signal (S5) and dependent on the value of the DC component (S5g) of the transmission signal (S5). In the following, we assume that the value (s5) of the transmission signal (S5) thus comprises a constant direct component value (s5g) of the transmission signal (S5) and a transmission signal alternating component value (s5w). The following equation describes this:

[0236] $s5=s5g+s5w$

[0237] This gives us:

[0238] $i1=h{0}^{{ }_{}\prime }+{\mathrm{hRA}}^{{ }_{}\prime }+\mathrm{h1}+\mathrm{hRb}+h1*s5g+h1*s5w+\mathrm{hRb}*s5w+\mathrm{hRb}*s5g$

[0239] We summarize the constant terms h0′+h1+h1*s5g=h0 and hRa′+hRb+hRb*s5g=hRa and obtain:

[0240] $i1=h0+\mathrm{hRa}+h1*s5w+\mathrm{hRb}*s5w$

[0241] A first portion a1 of this pump radiation (LB) hits the sensor element and the paramagnetic centers (NV1) contained therein. The paramagnetic centers (NV1) convert a second portion a2 of this pump radiation (LB) into fluorescence radiation (FL) with an intensity ifl, which reaches a first optical filter (F1). After interaction with the sensor element, the intensity id of the pump radiation (LB) is reduced to a third fraction a3 which reaches the first optical filter (F1).

[0242] The intensity ifi of the radiation in the first transmission path (I1) reaching the first optical filter (F1) is then described in equation II below:

[0243] $\mathrm{ifi}=a2*a1*\left(h0+\mathrm{hRa}+h1*s5w+\mathrm{hRb}*s5w\right)+a3*a1*\left(h0+\mathrm{hRa}+h1*s5w+\mathrm{hRb}*s5w\right)$

[0244] For simplicity, we assume here an ideal optical transmission of the fluorescence radiation (FL) through the first optical filter (F1) and an ideal blocking of the optical transmission of the pump radiation (LB) through the first optical filter (F1). The intensity ift of the radiation in the first transmission path (I1) passing the first optical filter (F1) is then described in the following equation III:

[0245] $\mathrm{ift}=a2*a1*\left(h0+\mathrm{hRa}+h1*s5w+\mathrm{hRb}*s5w\right)$

[0246] In the ideal case, therefore, only fluorescence radiation (FL) reaches the radiation receiver (PD). This is an approximation that comes close to reality. The intensity ifd of the fluorescence radiation (FL) reaching the radiation receiver (PD) is reduced once again to a fourth fraction a4. This describes equation IV:

[0247] $\mathrm{ifd}=a4*a2*a1*\left(h0+\mathrm{hRa}+h1*s5w+\mathrm{hRb}*s5w\right)$

[0248] At the same time, only a fifth portion a5 of the intensity (I_ks) of the compensation radiation (KS) emitted by the compensation radiation source (PLK) reaches the radiation receiver (PD). This radiation intensity i2 in the second transmission path (I2) depends on the value of the compensation transmission signal (S7). The following equation V describes the radiation intensity i2 emitted by the compensation radiation source (PLK).

[0249] $i2=k0+\mathrm{kRa}+k1*s7w+\mathrm{kRb}*s7w$

[0250] Here, k0 stands for an offset constant. k1 stands for a proportionality factor. kRa stands for a noise component that is independent of the alternating component s7w of the compensation transmission signal (S7). s7w stands for the value of the alternating component of the compensation transmission signal (S7). While we explicitly assume here in this paper that the noise of the compensation radiation source (PLK) is similar to that of the pump radiation source (PL1), we first take a potential dissimilarity for clarification, since similarity is a stretchable term.

[0251] Equation VI then describes the fraction ik of the intensity (I_ks) of the compensating radiation (KS) that reaches the radiation receiver (PD).

[0252] $\mathrm{ik}=a5*\left(k0+\mathrm{kRa}+k1*s7w+\mathrm{kRb}*s7w\right)$

[0253] The intensity of the total radiation ig reaching the radiation receiver (PD) is now calculated according to equation VII:

[0254] $\mathrm{Ig}=\mathrm{ik}+\mathrm{ifd}=a5*\left(k0+kRa+k1*s7w+\mathrm{kRb}*s7w\right)+a4*a2*a1*\left(h0+hRa+h1*s5w+\mathrm{hRb}*s5w\right)$

[0255] The radiation receiver (PD) now generates a receiver output signal (S0) as a function of the intensity ig of the total radiation reaching it. Equation VIII describes this:

[0256] $s0=d0+\mathrm{dRs}+d1*\mathrm{ig}+\mathrm{dRb}*\mathrm{ig}$

[0257] Where s0 represents the value of the receiver output signal (S0). do represents an offset constant. d1 represents a proportionality factor. dRa represents a noise of the radiation receiver (PD) that does not depend on the value of the total intensity ig of the radiation hitting the radiation receiver (PD). dRb represents a noise of the radiation receiver (PD) that depends on the value of the total intensity ig of the radiation hitting the radiation receiver (PD). Substitution yields equation IX:

[0258] $S0=d0+d\mathrm{Ra}+d1*a5*\left(k0+kRa+k1*s7w+\mathrm{kRb}*s7w\right)+d1*a4*a2*a1*\left(h0+hRa+h1*s5w+\mathrm{hRb}*s5w\right)+\mathrm{dRb}*a5*\left(k0+kRa+k1*S7+\mathrm{kRb}*s7w\right)+\mathrm{dRb}*a4*a2*a1*\left(h0+hRa+h1*s5w+\mathrm{hRb}*s5w\right)$

[0259] We require that the alternating component (s5w) of the transmission signal (S5) has, at least some of the time, a transmission signal period (T_P) with a transmission signal period duration (T_P), where the integral of the value of the alternating component (s5w) of the value (s5) of the transmission signal (S5) vanishes over this transmission signal period duration (T_P). We express this in equation X:

[0260] ${\int }_0^{T_p}s5w\mathrm{dt}=0$

[0261] This periodicity condition will become very important later. We now multiply the value (s5w) of the alternating component (S5w) of the transmission signal (S5) by the value (s0) of the receiver output signal (S0) and obtain the value (s3) of the filter input signal (S3). In the sensor system, a first multiplier (M1) preferably performs this multiplication of the value (s0) of the receiver output signal (S0) by the value (s5w) of the alternating component (S5w) of the transmission signal (S5) to the value (s3) of the filter input signal (S3). This value (s3) of the filter input signal (S3) is described by equation XI:

[0262] $s3=\left[d0+\mathrm{dRa}+d1*a5*\left(k0+\mathrm{kRa}+k1*s7w+\mathrm{kRb}*s7w\right)+d1*a4*a2*a1*\left(h0+\mathrm{hRa}+h1*s5w+\mathrm{hRb}*s5w\right)+\mathrm{dRb}*a5*\left(k0+\mathrm{kRa}+k1*s7w+\mathrm{kRb}*s7w\right)+\mathrm{dRb}*a4*a2*a1*\left(h0+\mathrm{hRa}+h1*s5w+\mathrm{hRb}*s5w\right)\right]*s5w$

[0263] Multiplying out equation XI gives equation XII:

[0264] $$\begin{gathered} s3=d0*s5w+\mathrm{dRa}*s5w+d1*A5*k0*s5w+d1*A5*\mathrm{kRa}*s5w+d1*A5*k1*s7w*s5w+ \\ d1*A5*\mathrm{kRb}*s7w*s5w+d1*A4*A2*A1*h0*s5w+d1*A4*A2*A1*\mathrm{hRa}*s5w+d1*A4*A2*A1*h1*s5w*s5w+d1*A4*A2*A1*\mathrm{hRb}*s5w*s5w+A5*k0*\mathrm{dRb}*s5w+A5*\mathrm{dRb}*\mathrm{kRa}*s5w+A5*k1*\mathrm{dRb}*s7w*s5w+A5*\mathrm{dRb}*\mathrm{kRb}*s7w*s5w+\mathrm{dRb}*A4*A2*A1*h0*s5w+\mathrm{dRb}*A4*A2*A1*\mathrm{hRa}*s5w+\mathrm{dRb}*A4*A2*A1*h1*s5w*s5w+ \\ d\mathrm{Rb}*A4*A2*A1*\mathrm{hRb}*s5w*s5w \end{gathered}$$

[0265] We now use a linear filter with the filter function F[X1]. Let X1 and X1 be the two values of any two signals. Let x be any real factor. A filter with the filter function F[X1] is a linear filter for the purposes of this disclosure if (Equation XIII) holds:

[0266] $F\left[X1+X2\right]=F\left[X1\right]+F\left[X2\right]$ $F\left[x*X1\right]=x*F\left[X1\right]$

[0267] We now use a loop filter (TP), which is supposed to be a linear filter with filter function F[s3], to filter the filter input signal (S3) to the filter output signal (S4), so the value (s3) of the filter input signal (S3) is supposed to be the variable of the filter function F[s3].

[0268] The structure of the loop filter (TP) is chosen such that at least approximately holds (Equations XIVa to XIVc):

[0269] $F\left[s5w\right]=0$ $F\left[s5w*s5w\right]=1$ $F\left[1\right]=1$

[0270] These conditions typically describe a low-pass filter. We will discuss this structure in more detail later. We assume here that equations XIVa to XIVc apply to the loop filter (TP).

[0271] For the value (s4) of the filter output signal (S4) of the loop filter (TP), we then find with a positive gain v of the loop filter (TP9 or an amplifier following the loop filter (TP) (Equation XV):

[0272] $s4=v*d0*F\left[s5w\right]+v*F\left[\mathrm{dRa}*s5w\right]+v*d1*a5*k0*F\left[s5w\right]+v*d1*a5*F\left[\mathrm{kRa}*s5w\right]+v*d1*a5*k1*F\left[s7w*s5w\right]+v*d1*a5*F\left[\mathrm{kRb}*s7w*s5w\right]+v*d1*a4*a2*a1*h0*F\left[s5w\right]+v*d1*a4*a2*a1*F\left[\mathrm{hRa}*s5w\right]+v*d1*a4*a2*a1*h1*F\left[\mathrm{s5w}*s5w\right]+v*d1*a4*a2*a1*F\left[\mathrm{hRb}*s5w*s5w\right]+v*a5*k0*F\left[\mathrm{dRb}*s5w\right]+v*a5*F\left[\mathrm{dRb}*\mathrm{kRa}*s5w\right]+v*a5*k1*F\left[\mathrm{dRb}*s7w*s5w\right]+v*a5*F\left[\mathrm{dRb}*\mathrm{kRb}*s7w*s5w\right]+v*a4*a2*a1*h0*F\left[\mathrm{dRb}*s5w\right]+v*a4*a2*a1*F\left[\mathrm{dRb}*\mathrm{hRa}*s5w\right]+v*a4*a2*a1*h1*F\left[\mathrm{dRb}*s5w*s5w\right]+v*a4*a2*a1*F\left[\mathrm{dRb}*\mathrm{hRb}*s5w*s5w\right]$

[0273] We assume that the multiplication of two noise terms can be neglected and apply Equations XIV (Equation XVI):

[0274] $s4=+v*F\left[\mathrm{dRa}*s5w\right]+v*d1*a5*F\left[\mathrm{kRa}*s5w\right]+v*d1*a5*k1*F\left[s7w*s5w\right]+v*d1*a5*F\left[\mathrm{kRb}*s7w*s5w\right]+v*d1*a4*a2*a1*F\left[\mathrm{hRa}*s5w\right]+v*d1*a4*a2*a1*h1+v*d1*a4*a2*a1*F\left[\mathrm{hRb}*s5w*s5w\right]+v*a5*k0*F\left[\mathrm{dRb}*s5w\right]+v*a5*k1*F\left[\mathrm{dRb}*s7w*s5w\right]+v*a4*a2*a1*h0*F\left[\mathrm{dRb}*s5w\right]+v*a4*a2*a1*h1*F\left[\mathrm{dRb}*s5w*s5w\right]$

[0275] We now multiply the value (s4) of the filter output signal (S4) by the value (s5c) of the complementary transmission signal (S5c) by means of multiplication. Here, let s5c=1−S5w hold, where we assume that the maximum value of the value (s5w) of the alternating component (S5w) of the transmission signal (S5) has an exemplary simplifying magnitude of 1. We further provide the value (s6) of the feedback signal (S6) thus obtained with an offset (b0) to obtain the value (s7) of the compensation transmission signal (S7). The prerequisite is that the L2 norm F[s5w*s5w]=1 applies:

[0276] $s7=\left[\left(1-s5w\right)*s4+b0\right]$

[0277] For simplicity, we have assumed here that for the amplitude (s5W_A) of the time-value response of the alternating component (S5w) of the transmission signal (S5), s5w_A=1. Otherwise, F[s5w*s5w]=s5w_A² would have to be used here.

[0278] In our sensor system, a second multiplier (M2) is used for the multiplication. The second multiplier (M2) preferably multiplies the value (s4) of the filter output signal (S4) with the value (s5c) of the complementary transmission signal (S5c).

[0279] Insertion results in:

[0280] $s4=+v*F\left[\mathrm{dRa}*s5w\right]+v*d1*a5*F\left[\mathrm{kRa}*s5w\right]+v*d1*a5*k1*F\left[\left(\left(1-s5w\right)*s4+b0\right)*S5\right]+v*d1*a5*F\left[\mathrm{kRb}*\left(\left(1-s5w\right)*s4+b0\right)*s5w\right]+v*d1*a4*a2*a1*F\left[\mathrm{hRa}*s5w\right]+v*d1*a4*a2*a1*h1+v*d1*a4*a2*a1*F\left[\mathrm{hRb}*s5w*s5w\right]+v*a5*k0*F\left[\mathrm{dRb}*s5w\right]+v*a5*k1*F\left[\mathrm{dRb}*\left(\left(1-s5w\right)*s4+b0\right)*s5w\right]+v*a4*a2*a1*h0*F\left[\mathrm{dRb}*s5w\right]+v*a4*a2*a1*h1*F\left[\mathrm{dRb}*s5w*s5w\right]$

[0281] Dissolving the parentheses and applying the filter properties of the filter function F[ ] yields:

[0282] $s4=+v*F\left[\mathrm{dRa}*s5w\right]+v*d1*a5*F\left[\mathrm{kRa}*s5w\right]+v*d1*a5*k1*F\left[s4*s5w\right]-v*d1*a5*k1*F\left[S4*s5w*s5w\right]+v*d1*a5*k1*b0*F\left[s5w\right]+v*d1*a5*F\left[\mathrm{kRb}*S4*s5w\right]-v*d1*a5*F\left[\mathrm{kRb}*s4*s5w*s5w\right]+v*d1*a5*F\left[b0*\mathrm{kRb}*s5w\right]+v*d1*a4*a2*a1*F\left[\mathrm{hRa}*s5w\right]+v*d1*a4*a2*a1*h1+v*d1*a4*a2*a1*F\left[\mathrm{hRb}*s5w*s5w\right]+v*a5*k0*F\left[\mathrm{dRb}*s5w\right]+v*a5*k1*F\left[\mathrm{dRb}*s4*s5w\right]-v*a5*k1*F\left[\mathrm{dRb}*s4*s5w*s5w\right]+v*a5*k1*b0*F\left[\mathrm{dRb}*s5w\right]+v*a4*a2*a1*h0*F\left[\mathrm{dRb}*s5w\right]+v*a4*a2*a1*h1*F\left[\mathrm{dRb}*s5w*s5w\right]$

[0283] Furthermore, we assume the value (s4) of the filter output signal (S4) to be almost constant in the steady state and can therefore then treat the factor s4 as a constant. We also use F[s5w]=0 and F[s5w*s5w]=1 where we simplifying assume s5W_A=1 for the amplitude s5W_A of the alternating component s5w of the transmission signal (S5).

[0284] $s4=+v*F\left[\mathrm{dRa}*\mathrm{s5w}\right]+v*d1*a5*F\left[\mathrm{kRa}*s5w\right]-v*d1*a5*k1*s4+v*d1*a5*s4*F\left[\mathrm{kRb}*s5w\right]+v*d1*a5*s4*F\left[\mathrm{kRb}*s5w*s5w\right]+v*d1*a5*b0*F\left[\mathrm{kRb}*s5w\right]+v*d1*a4*a2*a1*F\left[\mathrm{hRa}*s5w\right]+v*d1*a4*a2*a1*h1+v*d1*a4*a2*a1*F\left[\mathrm{hRb}*s5w*s5w\right]+v*a5*k0*F\left[\mathrm{dRb}*s5w\right]+v*a5*k1*s4*F\left[\mathrm{dRb}*s5w\right]+v*\mathrm{a5}*k1*S4*F\left[\mathrm{dRb}*s5w*s5w\right]+v*a5*k1*b0*F\left[\mathrm{dRb}*s5w\right]+v*a4*a2*a1*h0*F\left[\mathrm{dRb}*s5w\right]+v*a4*a2*a1*h1*F\left[\mathrm{dRb}*s5w*s5w\right]$

[0285] We assume that the constant signal component of the product s5w*s5w carries through in the loop filter (TP) and, based on this assumption, use the equations that then apply F[KRb+s5w*s5w]=F[kRb], F[dRb+s5w*s5w]=F[dRb] and F[hRb*s5w*s5w]=F[hRb]:

[0286] $s4=+v*F\left[\mathrm{dRa}*s5w\right]+v*d1*a5*F\left[\mathrm{kRa}*s5w\right]-v*d1*a5*k1*s4+v*d1*a5*s4*F\left[\mathrm{kRb}*s5w\right]+v*d1*a5*s4*F\left[k\mathrm{Rb}\right]+v*d1*a5*b0*F\left[\mathrm{kRb}*s5w\right]+v*d1*a4*a2*a1*F\left[\mathrm{hRa}*s5w\right]+v*d1*a4*a2*a1*h1+v*d1*a4*a2*a1*F\left[hRb\right]+v*a5*k0*F\left[\mathrm{dRb}*s5w\right]+v*a5*k1*s4*F\left[\mathrm{dRb}*s5w\right]-v*a5*k1*s4*F\left[d\mathrm{Rb}\right]+v*a5*k1*b0*F\left[\mathrm{dRb}*s5w\right]+v*a4*a2*a1*h0*F\left[\mathrm{dRb}*s5w\right]+v*a4*a2*a1*h1*F\left[dRb\right]$

[0287] This is equivalent to:

[0288] $s4\left(1+v*d1*a5*k1-v*d1*a5*F\left[\mathrm{kRb}*s5w\right]-v*a5*k1*F\left[\mathrm{dRb}*s5w\right]+v*a5*k1*F\left[\mathrm{dRb}\right]+v*d1*a5*F\left[\mathrm{kRb}\right]\right)=+v*F\left[\mathrm{dRa}*s5w\right]+v*d1*a5*F\left[\mathrm{kRa}*s5w\right]+v*d1*a5*B0*F\left[\mathrm{kRb}*s5w\right]+v*d1*a4*a2*a1*F\left[\mathrm{hRa}*s5w\right]+v*d1*a4*a2*a1*h1+v*d1*a4*a2*a1*F\left[\mathrm{hRb}\right]+v*a5*k0*F\left[\mathrm{dRb}*s5w\right]+v*a5*k1*b0*F\left[\mathrm{dRb}*s5w\right]+v*a4*a2*a1*h0*F\left[\mathrm{dRb}*s5w\right]+v*a4*a2*a1*h1*F\left[\mathrm{dRb}\right]$