Method and device for evaluating a measurement signal emitted by an NV quantum system

Abstract

The invention relates to a method for evaluating a measurement signal (5') emitted by an NV quantum system (4). The NV quantum system (4) is initialised using pulsed excitation light (13, 320) and is subjected to an alternating magnetic field (3; 310) which alternately assumes two different field states. The measurement signal (5') emitted by the NV quantum system (4) is detected and integrated over an integration window (331) that includes a signal time of a first light pulse (322) in order to obtain a signal value, and over an integration window (332) that includes a signal time of a second light pulse (322) in order to obtain a reference value, wherein the first and the second light pulses are two temporally offset light pulses of the excitation light (13; 320), wherein the first light pulse (322) is generated after the alternating magnetic field (3; 310) has assumed a first of the two field states, and wherein the second light pulse (322) is generated after the alternating magnetic field (3; 310) has assumed a second of the two field states. A measurement value is determined from the signal value and the reference value.

Description

[0001] R.410058

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method and device for evaluating a measurement signal emanating from an NV quantum system

[0006] The present invention relates to a method and a device for evaluating a measurement signal emanating from an NV quantum system.

[0007] Background of the invention

[0008] To measure very small magnetic field strengths, guant-based or optically pumped magnetometers are particularly suitable as sensors. Such magnetometers often utilize optically pumped and optically detected magnetic resonances (ODMR). This method exploits the fact that, under the influence of an external magnetic field, the energy levels of certain spin states of unpaired electrons split—the so-called Zeeman effect. This energy level splitting results in altered relaxation transitions from excited states, which can then be measured, for example, by optical excitation and frequency-dependent detection of the resulting fluorescence radiation, or by observing optical properties such as light absorption. The magnetic field strength can then be deduced from the measured optical parameters.

[0009] For such guanine-based magnetic field sensors, sensor crystals with excitable defect centers can be used. Typically, diamonds homogeneously doped with negative nitrogen vacancy centers (NV centers) are employed. The quantum state preparation is carried out via R.410058.

[0010] - 2 - optical excitation and the interaction with a static magnetic field and a dynamic magnetic field, i.e. a microwave field.

[0011] For measuring very small magnetic field strengths, quantum-based magnetic sensors based on nitrogen-vacancy centers are known, for example, from DE 10 2018 220 234 A1 or DE 10 2018 214 617 A1. In these sensors, the information stored in the spin system is read out optically by detecting the spin-state-dependent fluorescence rates of the nitrogen-vacancy center. Therefore, the accuracy is limited, among other things, by the signal-to-noise ratio of the optical readout method of the nitrogen-vacancy center.

[0012] In general, spin-based sensor arrays (also referred to here as quantum sensors) detect and evaluate pulsed signals, for which a self-referencing method can be used. When evaluating a measurement signal, a contrast can be calculated that indicates the spin state of the electron spin. For this purpose, the measurement signal can be integrated over an integration window containing a signal time point of a light pulse to obtain a signal value, and conversely, it can be integrated over an integration window containing a reference time point of the light pulse to obtain a reference value. A measured value can be determined from the signal value and the reference value, e.g., as a quotient. The integration window containing the reference time point typically covers a period in the measurement signal during which no useful information is present, but only background information, a zero signal, or a baseline signal.In contrast, the integration window at the signal time is typically chosen to contain the maximum information density, i.e., to achieve an optimal signal-to-noise ratio. This allows the measurement result to be decoupled from the measured photon flux and suppresses intensity noise.

[0013] In DE 10 2023 209 716.8 a method is proposed in which a spin-based quantum system is excited by a pulsed excitation light, a measurement signal emanating from the NV quantum system is detected, the measurement signal is integrated via an integration window containing a signal time of an R.410058

[0014] - 3 - first light pulse and is integrated over an integration window containing a signal time of a second light pulse to obtain a signal value and a reference value, wherein the first and second light pulses are two time-off light pulses of the excitation light, and a measured value is determined from the signal value and the reference value.

[0015] Disclosure of the invention

[0016] According to the invention, a method and a device for evaluating a measurement signal emanating from an NV quantum system are proposed, comprising the features of the independent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0017] In an NV center in a diamond, the spin ground state is a triplet in which (without an external magnetic field) at T=0 K there is an energy difference corresponding to 2.87 GHz between spin |m s = 0> on the one hand and spin |m s= ±1 > on the other hand, there is (zero-field splitting). The zero-field splitting is temperature-dependent by a factor of approximately -74.2 kHz / K, which corresponds to a shift of the measured magnetic field by approximately 2.6 pT / K. An external magnetic field splits the two states (Zeeman effect), so that now for each transition |m s = 0>— >|m s = -1 > and |m s = 0>— >|m s = +1> a separate energy difference can be measured, from which the external magnetic field can be determined.

[0018] Another source of error is the frequency drift of the microwave source used to sample the ODMR spectrum. This has a linear effect on the measurement, similar to a temperature drift.

[0019] Within the scope of the invention, two measurements are specifically carried out at the different transitions in such a way that temperature compensation becomes possible. R.410058

[0020] - 4 - In particular, the NV quantum system is excited by a pulsed excitation light in order to put the NV quantum system into the spin state |m s = 0> to initialize, and is excited by an alternating magnetic field which alternately or simultaneously has two different field states, whereby the NV quantum system is brought into the spin state |m by an alternating magnetic field which has the first of the two field states. s = +1> can be converted, and into the spin state |m by an alternating magnetic field which has the second of the two field states. s = -1 > can be converted.

[0021] Typical frequency values ​​of magnetic fields used to excite NV quantum systems lie in the high-frequency range, specifically in the microwave range. The abbreviation "HF" will also be used for "high frequency" in the following text. The frequency of the high-frequency field (HF field) depends on the energy difference (corresponding to a frequency) between the quantum mechanical states of the quantum system between which transitions are to be induced.

[0022] The measurement signal emanating from the NV quantum system is acquired and integrated via an integration window containing a signal time of a first light pulse to obtain a signal value, and integrated via an integration window containing a signal time of a second light pulse to obtain a reference value, wherein the first and the second light pulse are two time-shifted light pulses of the excitation light, wherein the first light pulse lies after the alternating magnetic field which has the first of the two field states, and wherein the second light pulse lies after the alternating magnetic field which has the second of the two field states.

[0023] Advantageously, the light pulses are readout pulses, and further advantageously, two immediately consecutive readout pulses.

[0024] A measured value can be determined from the signal value and the reference value, e.g. as a quotient or difference, or as a quotient of a difference between R.410058

[0025] - 5 -

[0026] Signal value and reference value, and a sum of signal value and reference value. A measured value determined in this way expresses a contrast in the measurement signal.

[0027] For example, this results in the following calculation formula: contrastdifferentai = 2 (signal+ - signal-) / (signal+ + signal-) where contrastdifferentai is the measured value, signal+ is the signal value, and signal is the reference value.

[0028] Furthermore, normalization to the sum of the signal value and the reference value compensates for fluctuations in the signal value, leading to increased robustness against variations in the excitation power density. This enhances the system's robustness and allows the sensor system to achieve a sensitivity comparable to a system with two photodiodes, which achieves such fluctuations by balancing the photodiode signal, without requiring a dedicated balancing circuit.

[0029] In this context, it should be noted that a readout pulse for one measurement can simultaneously be the excitation pulse for a subsequent measurement. Likewise, it should be noted that the reference value of one measurement can simultaneously be the signal value of the next measurement.

[0030] The invention allows for temperature-compensated measurement by correctly selecting the resonance line or spectral line, as the temperature effect is factored out during measurement. This utilizes the different interactions of the NV center with temperature changes and changes in the magnetic field. In the fluorescence spectrum, where fluorescence intensity is plotted against frequency, a magnetic field splits the resonance lines or resonance frequencies of the NV center, while a temperature change shifts the resonance lines in the same direction. (Measures R.410058)

[0031] - 6 - if the signal value and the reference value are now measured at resonance lines of different spin transitions, i.e. to the right and left of the fundamental resonance (2.87 GHz), the temperature shift cancels each other out.

[0032] In embodiments of the invention, the method can be a pulsed ODMR measurement. By selecting the correct resonance edges, the calculated signal is independent of a shift of both resonance frequencies in the same direction and is therefore temperature-compensated.

[0033] In embodiments of the invention, measurements are not taken at the crest of the resonance line, but rather on its flank. The two measurement points or frequencies are selected such that they both lie on a rising or both on a falling flank of the resonance line in the fluorescence spectrum, in which the fluorescence intensity is plotted against the frequency. It should be noted that a resonance line in the spectrum is not a sharp line, but rather has a peak shape (see Fig. 2a). The measurement point is therefore shifted by a value df relative to the crest of the resonance line. Advantageously, the measurement point corresponds to the point of maximum slope in the spectrum and thus to the sensitivity maximum. This ensures that the points with the highest information content are sampled, while possible intermediate measurement points are not measured. This has the advantage that the useful signal can be measured fully scaled (i.e., with maximum amplitude).

[0034] In other words, in embodiments of the invention, the two field states are chosen such that the measurement signal in the integration window at the signal time of the first light pulse has a slope with a different sign than the measurement signal in the integration window at the signal time of the second light pulse.

[0035] In other words, the difference between a "positive" and a "negative" edge (signal rises / falls with a change in the magnetic field) is determined, with the edges corresponding to peaks of different transitions (|m s = 0>— >|m s = -1>, R.410058

[0036] - 7 -

[0037] |m s = 0>— >|m s = +1>), and, if they are not on the vertex, both are shifted in the same frequency direction starting from the vertex.

[0038] Another way to measure the shift of a resonant frequency is to use quantum mechanical superposition states. A typical protocol here is, for example, free induction decay (FID, also called the Ramsey protocol) or the Hahn echo. In this process, a quantum mechanical superposition state is generated and freely evolved for one evolutionary time. This state oscillates with the resonant frequency (Lamor frequency), and the phase between this oscillation and the microwave frequency is measured at the end.

[0039] A typical pulse sequence (FID) is - T - The first pulse prepares the superposition state. This is followed by a time evolution T, during which a phase is collected due to the frequency difference between the Lamor precision and the microwave. This phase difference is then converted into a population difference with the last pulse, which can then be read out.

[0040] In embodiments of the invention, a pulse sequence is now proposed in which the ^-pulses in each measurement between the transitions |m s = 0>— >|m s = -1 > and |m s = 0>— >|m s = +1>). The pulses are at different frequencies, each corresponding to a specific transition. This means that, for temperature compensation, the measurement sequence between transitions must be adjusted.

[0041] |m s = 0>— >|m s = -1> and |m s = 0>— >|m s = +1>). Then the sign for a change in the magnetic field (distance between resonances increases) is opposite, and for a change in temperature, it is the same. This also allows for temperature compensation here.

[0042] It is advantageous to measure on the same resonance line as the hyperfine splitting of the resonance line. Due to the interaction of the electron spin with the nuclear spin, the resonance lines split further, with NV centers exhibiting this effect. 14 N-lon three hyperfine lines per resonance line visible in the spectrum R.410058

[0043] - 8 - are. The measurement should therefore take place on either the left, middle or right hyperfine line at both transitions.

[0044] According to one embodiment, NV centers in diamonds are bonded to the nitrogen isotope 15 N is used. Since nitrogen 15 Since N only has two nuclear spin levels, the NV centers are equipped with 15 N-lon shows only two hyperfine lines per resonance line in the spectrum. This makes it possible to directly generate a temperature-compensated signal by placing a hyperfine line on the transition |m s = 0>— >|m s= +1> and the other hyperfine line on the transition |m s = 0>— >|m s = -1> is measured.

[0045] The advantage of using 15 The advantage is that both sub-ensembles (determined by the nuclear spin state, which remains unchanged) can be addressed in a single measurement, thus allowing the construction of a measurement procedure in which both edges are sampled in one measurement. For example, this is possible by using a transition (e.g., m s = 0>— >|m s = -1>) on the nuclear spin sub-ensemble mi=-1 / 2 and the other transition (e.g. m s = 0>— >|m s= +1 >) samples the nuclear spin sub-ensemble mi=+1 / 2. Since the signals from the nuclear spin sub-ensembles superimpose during readout, the influence of a shift (temperature) can be directly compensated for in the measurement. This also allows errors of the microwave source, such as phase noise, to be directly compensated, which enables the use of less expensive components. When using 14 In such a measurement, only 2 out of 3 hyperfine transitions can be used, which means a lower sensitivity of the sensor.

[0046] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0047] The invention is schematically illustrated in the drawing using exemplary embodiments and is described below with reference to the drawing.

[0048] Brief description of the drawings R.410058

[0049] - 9 -

[0050] Figure 1 shows an exemplary fluorescence spectrum of an NV quantum system, where the fluorescence intensity is plotted against the frequency of the alternating magnetic field.

[0051] Figure 2 shows in view a) the signal waveform and in view b) the derivation of the signal waveform of hyperfine splittings with three nuclear spin levels (e.g. 14 N) each of one m s = 0>— >|m s = -1 > transition and one m s = 0>— >|m s = +1 > Transition from Figure 1 in enlarged view.

[0052] Figure 3 shows in view a) the signal waveform and in view b) the derivation of the signal waveform of hyperfine splittings with two nuclear spin levels (e.g. 15 N) each of one m s = 0>— >|m s = -1 > transition (left) and one m s = 0>— >|m s = +1> Transition (right).

[0053] Figure 4 schematically shows a device for generating a measurement signal from a signal emanating from an NV quantum system according to an embodiment of the invention in a block diagram.

[0054] Figure 5 shows a sequence for a measurement according to an embodiment of the invention.

[0055] embodiment(s) of the invention

[0056] Diamond nitrogen vacancy magnetometers are based on the detection of magnetic resonances from specific nitrogen vacancies (NV) in diamond. These vacancies occur as impurities in the diamond's carbon lattice and can also be introduced intentionally. A nitrogen vacancy center is a pair consisting of a nitrogen atom, which replaces a single carbon atom in the diamond lattice, and an adjacent vacancy in the lattice. When the NV center is optically excited in its normal state without a magnetic field, for example by a pump laser beam with a suitable wavelength (in this case, R.410058), a magnetic resonance is detected.

[0057] - 10 -

[0058] If light is irradiated in the green wavelength range (e.g., at 532 nm for off-resonance excitation), the electrons are excited from the triplet ground state to the excited triplet state and relax, emitting fluorescence light in the red wavelength range at 637 nm. Since the probability of non-spin-conserving transitions from the spin state with spin quantum number m s If the value is greater than ±1, continuous excitation pumping ensures that the NV centers are mostly in the spin state m s =0 polarized.

[0059] Between the m s = 0 and m s There is an energy difference of ±1 between spin states in the ground state, which in this case is approximately 2.87 GHz. Therefore, if microwave radiation is also applied to the diamond in addition to optical excitation, a dip in the red fluorescence occurs at this resonance frequency of 2.87 GHz, as the spin-polarized electrons are disturbed by the microwave field.s = 0 in the m s = ±1 -ground state can be raised and from there into the m by the pump light s =±1 excited state. From there, however, mainly non-radiative transitions and weakly infrared fluorescence transitions occur via the singlet state, while fluorescence in the red region disappears.

[0060] If an external magnetic field is present, the so-called Zeeman effect causes the otherwise identically energetic magnetic fields to split. s= ±1 triplet levels in energetically equidistant Zeeman levels. When the fluorescence is plotted against a frequency spectrum of the microwave excitation, two dips or (negative) peaks appear in the fluorescence spectrum, whose frequency separation is linearly proportional to the magnetic field strength of the external magnetic field. The magnetic field sensitivity is primarily defined by the minimum resolvable frequency shift and can reach up to 1 pTA / Hz. Each of these dips consists of three hyperfine dips at high resolution (see Fig. 1).

[0061] Since the NV center in the single-crystal diamond lattice has four possible orientations, in the presence of a directed magnetic field, the different NV centers present in the crystal are oriented according to their orientation R.410058

[0062] - 11 - react differently to the external magnetic field. In the zero field, i.e., without an applied magnetic field or at very small fields, the spin transitions of all four orientations are excited at essentially the same microwave frequency, so that the observed resonance corresponds to the sum of all orientations and produces only a dip in the spectrum. However, as soon as an external magnetic field is applied, frequency splitting occurs in the resonance spectrum, as described above in general terms. Thus, if the existing magnetic field has different field components in all four possible axes, tuning the microwave frequency yields four separate pairs of fluorescence minima in the spectrum, where the strength of the splitting (i.e., the observed frequency separation) depends on the strength of the respective magnetic field component. If the applied external directed magnetic field is increased, the two minima of a pair move further apart.

[0063] Another property of NV centers is that their energy levels also respond to temperature changes. When the crystal is heated, the distance between the ground level |m decreases. s = 0> and the level |m s = ±1 >, which is accompanied by a uniform frequency shift of the associated fluorescence minima.

[0064] Figure 1 shows a corresponding exemplary resonance spectrum under the influence of an external directed magnetic field, where the fluorescence intensity I on the y-axis is plotted against the microwave frequency f in MHz on the x-axis. Eight fluorescence minima are visible, with the resonance lines in four spatial directions: two Zeeman lines (one to the right and one to the left of the center) and three hyperfine lines (for 14 N). From such a spectrum, both the magnetic field strength and the direction of the external magnetic field can be uniquely determined.

[0065] In Fig. 1, two possible measurement points or frequencies of the alternating magnetic field are marked with an arrow. These correspond to different transitions (to the right and left of the center), but to the same spatial direction (outermost group of three in each case) and to the same hyperfine line. R.410058

[0066] - 12 -

[0067] In Fig. 2a, the corresponding resonance lines are shown enlarged, and in Fig. 2b, their derivatives dl / df are shown. The points with the maximum slope, i.e., signal change dl / df, are marked with arrows. Fig. 2 clearly shows that a shift of the resonance line in the same direction—especially due to a temperature change—leads to the same signal change at both measurement points; that is, both signals either increase or decrease. By comparating the two signals, the temperature change is thus compensated (in simpler terms, the difference remains the same).

[0068] By always choosing the edge in relation to the central frequency on the same side, the splitting due to a changed field is added, but the shift of the entire spectrum due to, for example, temperature changes or microwave frequency drifts is compensated.

[0069] It should be noted that the figures are only to be understood as illustrating the operating principle and that it is not a single NV center that generates these different frequency splittings, but rather that the number of NV centers will be approximately equally distributed across the four possible orientations in a measurement range, so that all transitions in the spectrum can be observed.

[0070] Figure 3 shows in the upper diagram a) an exemplary resonance spectrum under the influence of an external directed magnetic field, where the fluorescence intensity I on the y-axis is plotted against the microwave frequency f in MHz on the x-axis. Two sets of two fluorescence minima are visible, with the resonance lines consisting of two Zeeman lines (one each to the right and left of the center at approximately 2.87 GHz) and two hyperfine lines (for 15 N). From such a spectrum, both the magnetic field strength and the direction of the external magnetic field can be uniquely determined.

[0071] In Fig. 3, two exemplary measurement configurations or measurement pairs of the alternating magnetic field are marked with arrows 210, 220, where the two R.410058

[0072] - 13 -

[0073] Fields or frequencies 210 are measured simultaneously, and the two fields or frequencies 220 are measured simultaneously.

[0074] Each measurement configuration involves two different transitions (right and left of center) and different hyperfine lines (but the same spatial direction (innermost pair in each case)). For temperature compensation, the edges of the same hyperfine line are not selected, but rather the edges of different hyperfine lines. By additionally selecting the edge always relative to the center frequency on the same side (i.e., for 210 always the outer edge relative to the center frequency, and for 220 the inner edge), one obtains an addition of the splitting caused by a changing field, but a compensation of the shift of the entire spectrum due to, for example, temperature changes or microwave frequency drifts. A shift of the resonance line in the same direction at both measurement points—especially one caused by a temperature change—leads to different signal changes; that is, one signal becomes stronger and the other weaker.By simultaneously measuring the two signals, the temperature change is compensated (in simple terms, the sum remains the same), i.e., temperature compensation is achieved with just one measurement.

[0075] In the signal waveforms shown in Fig. 3, a total of eight such measurement configurations can be selected.

[0076] In the first measurement, measurements are taken at frequencies 210, in the next measurement at frequencies 220, and then the frequency is alternated continuously.

[0077] To compensate for any signal differences, etc., all eight possible measurement pairs can be looped through, taking care to consider the resulting sign of the measurement signal, as it always has a changing polarity.

[0078] For example, will the transitions

[0079] |m s = 0>|mi = -1 / 2> — > |m s = +1 >|mi = -1 / 2> on the left flank and |m s= 0>|mi = +1 / 2> — > |m s = -1 >|mi = +1 / 2> on the right flank R.410058

[0080] - 14 - When measured simultaneously, only the influence of the magnetic signal (splitting of the electron spin transitions) is measured, while the influence of strain, temperature, and microwave noise (i.e., from the microwave source) averages out. This is particularly advantageous for achieving good sensitivities with, for example, less expensive hardware.

[0081] Figure 4 schematically shows a device 100 for evaluating a measurement signal 5' emanating from an NV quantum system 4 according to an embodiment of the invention in a block diagram.

[0082] The device 100 comprises an excitation light generation device 12 for generating a pulsed excitation light 13 and a field generation device 2 for generating an electromagnetic field 3 and the NV quantum system 4, which is to be excited by the excitation light 13 and the electromagnetic field.

[0083] The field-generating device 2 is configured to generate an electromagnetic field 3, in particular a high-frequency field (RF field), and further specifically a microwave field, which alternates or oscillates between two field states at a modulation frequency. The two field states can be different frequency values ​​that are equidistant from a center frequency.

[0084] The device 100 further comprises a measuring device 6 for capturing the measurement signal 5' emanating from the NV quantum system 4 in order to obtain a raw signal 7 which is transmitted to a computing unit 8.

[0085] The measurement signal 5' emanating from the NV quantum system 4 is, in certain configurations, a fluorescence signal or light signal. Accordingly, the measuring device 6 can, for example, comprise one or more photodiodes or a photodiode measurement arrangement. R.410058

[0086] - 15 -

[0087] The computing unit 8 is designed to evaluate the raw signal 7 and to control the field generation unit 2.

[0088] An exemplary measurement procedure is illustrated in Figure 5. Figure 5 shows a profile 310 of the microwave field 3, a profile 320 of the excitation light 13, and a profile 330 of integration windows.

[0089] Pulsed ODMR experiments conventionally comprise an initial light pulse (especially a laser pulse) 321 for spin polarization, a series of resonant microwave pulses 311 for spin manipulation, and a light pulse (especially a laser pulse) 322 for spin readout via the fluorescence intensity (readout pulse). In measurements of coherent spin rotation according to an FID scheme oa, the series of microwave pulses 311 can, for example, have the form - - T - - 2 2.

[0090] For example, the first rr / 2 pulse of a first row 311 prepares the coherent state |m s = 0> + |m s = -1>. Subsequently, a temporal evolution T occurs, in which a phase is collected due to the frequency difference between laser precision and microwave. This phase difference is then transferred to a population difference using the last TT / 2-PUIS, which can then be read out.

[0091] The first TT / 2-PUIS of a second, immediately following series 31 T, for example, prepares the state |m s = 0> + |m s = +1>. Subsequently, another temporal evolution T occurs, in which a phase is recorded due to the frequency difference between Lamor precision and microwave. This phase difference is then converted into a population difference using the last TT / 2-PUIS, which can then be read out. A measurement protocol can start with either series 311 or 311'. This only needs to be taken into account during demodulation.

[0092] It is specifically provided that a readout pulse 322 of a measurement is simultaneously the excitation pulse 321 of the subsequent measurement. Furthermore, R.410058

[0093] - 16 - in particular provided that the integration window 332 containing the reference time of the light pulse of a previous measurement simultaneously represents the integration window 331 containing the signal time of a light pulse of the subsequent measurement.

[0094] In other words, for a continuous output of measured values, the measured value at time (N+1) can be calculated from the signal value at time (N+1) and the signal value at time (N) with continuously changing signs. The following calculation formula results: contrastdifferentai(N+'\ > ) = [(-1) w signal N + (-1) w+1 signal N +-\] / (signal N + signalN+i) with: contrastdifferentai(N+'\ measured value at time N+1 signalN+i. Signal value or reference value at time N+1 signalN. Signal value or reference value at time N

[0095] This allows for a wider range of measurement data to be provided. Furthermore, the sensor's sensitivity is improved by a factor of up to 2 (square root of 2).

Claims

R.410058 - 17 - Claims 1. Method for evaluating a measurement signal (5') emanating from an NV quantum system (4), comprising the steps: Excitation of the NV quantum system (4) by a pulsed excitation light (13; 320) to bring the NV quantum system (4) into the spin state |m s = 0> to initialize, Excitation of the NV quantum system (4) by an alternating magnetic field (3; 310) which alternately has two different field states, wherein the NV quantum system (4) is excited to the spin state |m by an alternating magnetic field (3; 310) which has the first of the two field states. s = +1 > can be converted, and by an alternating magnetic field (3; 310), which has the second of the two field states, into the spin state |m s = -1> can be converted Capturing the measurement signal (5') emanating from the NV quantum system (4), Integrating the measurement signal (5') over an integration window (331) containing a signal time of a first light pulse (322) to obtain a signal value, Integrating the measurement signal (5') over an integration window (332) containing a signal time of a second light pulse (322) to obtain a reference value, wherein the first and second light pulses are two time-shifted light pulses of the excitation light (13; 320), wherein the first light pulse (322) is generated after the alternating magnetic field (3; 310) which has the first of the two field states, and wherein the second light pulse (322) is generated after the alternating magnetic field (3; 310) which has the second of the two field states, R.410058 - 18 - Determining a measured value from the signal value and the reference value.

2. Method according to claim 1, wherein it is a pulsed ODMR measurement, wherein the two field states correspond to two different frequencies of the alternating magnetic field (3; 310).

3. Method according to claim 2, wherein the two frequencies are selected such that they both lie on a rising or both on a falling edge of a peak in the fluorescence spectrum in which the fluorescence intensity is plotted against the frequency.

4. Method according to claim 1, wherein the measurement is of a coherent spin motion, wherein the two field states correspond to two different rr / 2 pulses.

5. Method according to any of the preceding claims, wherein the electromagnetic field (3; 310) is a microwave field.

6. Method according to any of the preceding claims, wherein the measurement signal (5') emanating from the NV quantum system (4) is a fluorescence signal or a light signal.

7. Method according to any of the preceding claims, comprising determining a measured value from the signal value and the reference value: Forming a quotient of the difference between the signal value and the reference value and the sum of the signal value and the reference value.

8. Method according to any one of the preceding claims, R.410058 - 19 - wherein the first and second light pulses are two immediately consecutive readout pulses of the excitation light (13; 320).

9. Method according to any of the preceding claims, wherein the NV quantum system (4) is essentially only 15 exhibits N atoms as defect centers.

10. Method according to claim 9, wherein it is a pulsed ODMR measurement, wherein each of the two field states comprises two different frequencies (210; 220) of the alternating magnetic field (3; 310).

11. Method according to claim 10, wherein the two frequencies (210; 220) of one of the two field states are selected such that one of the two frequencies (210; 220) lies on a rising edge of a first peak and the other of the two frequencies (210; 220) lies on a falling edge of a second peak in the fluorescence spectrum in which the fluorescence intensity is plotted against the frequency, wherein the first and the second peak belong to different hyperfine lines and to different nuclear spin transitions.

12. A method according to any one of the preceding claims, wherein the excitation of the NV quantum system (4) by the alternating magnetic field (3; 310), which has the first of the two field states, is carried out by a first TT / 2-PUIS of a first series 311 of rr / 2 pulses, which prepares a first superposition state, and wherein a temporal evolution T of the NV quantum system (4) is subsequently carried out following the first TT / 2-PUIS, and wherein a phase collected during the temporal evolution T is transferred into a population difference by a last TT / 2-PUIS of the first series 311, and wherein the excitation of the NV quantum system (4) by the alternating magnetic field (3; 310), which has the second of the two field states, is carried out by a first TT / 2-PUIS of a second series 31 T of rr / 2 pulses, which prepares a R.410058 - 20 - second superposition state prepared and wherein, following the first rr / 2 pulse of the second series 31 T of rr / 2 pulses, a temporal development T takes place, and wherein, with a last rr / 2 pulse of the second series 311 ', a phase collected during this temporal development T is transferred into a population difference.

13. Device (100) for evaluating a measurement signal (5') emanating from an NV quantum system (4), comprising: the NV quantum system (4), an excitation light generation device (12) for generating pulsed excitation light (13; 320), a field generation device (2) for generating an electromagnetic field (3; 310), wherein the NV quantum system (4) is arranged in the electromagnetic field (3; 310), and a measuring device (6) for detecting the signal emanating from the NV- quantum system (4) outgoing measurement signal (5'), wherein the device (100) is configured to perform a method according to one of the preceding claims.

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