Method and device for evaluating a measurement signal emitted by an NV quantum system
Patent Information
- Application Number
- PCT/EP2026/056897
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-03-28
- Filing Date
- 2026-03-12
- Publication Date
- 2026-10-01
Smart Images
Figure EP2026056897_01102026_PF_FP_ABST
Abstract
Description
[0001] R.416443
[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, guanine-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 are used that are homogeneously covered with negative nitrogen vacancies (R.416443).
[0010] - 2 -
[0011] The centers (NV centers, nitrogen vacancy) are doped. The preparation of the quantum state occurs via optical excitation and interaction with a static magnetic field and a dynamic magnetic field, i.e., a microwave field.
[0012] For measuring very small magnetic field strengths, quantum-based magnetic sensors based on nitrogen-vacancy centers are known, for example, from DE 102018220234 A1 or DE 102018214617 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.
[0013] Fundamentals of measurements on NV quantum systems are described, for example, in "Little bits of diamond: Optically detected magnetic resonance of nitrogenvacancy centers", Haimei Zhang et al., American Journal of Physics 86, 225 (2018); doi: 10.1119 / 1.5023389.
[0014] Disclosure of the invention
[0015] 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. A device according to the invention includes means for carrying out a method according to the invention. The features and advantages described below therefore apply equally to the method and the device.
[0016] 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 SpinR.416443
[0017] - 3 -
[0018] |m sOn the other hand, there is a zero-field splitting (±1). 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 for each transition |m s = 0>— >|m s = -1> and
[0019] |m s = 0>— >|m s = +1> a separate energy difference can be measured, from which the external magnetic field (B) can be determined.
[0020] Another source of error is the frequency drift of the microwave source used to sample the ODMR spectrum. This means that the difference or offset between an actual frequency and a target frequency is not constant over time but can fluctuate dynamically, even on short timescales. In other words, there is an uncertainty regarding the actual frequency of the applied microwave field, which alters the measurement signal of two successive measurements, even though the magnetic field being measured remains unchanged. Frequency drift affects the measurement linearly, similar to temperature drift. Both effects are collectively referred to as drift (D) in the following discussion.
[0021] While drift in the measurement signal can be compensated for by targeted measurements at different transitions, the magnitude of the drift is then unknown and cannot be taken into account during excitation; that is, the microwave frequency cannot be readjusted. Therefore, continuous measurement of a magnetic field is not possible.
[0022] This is where the invention comes in, proposing the simultaneous application of several microwave frequencies such that they belong to the same NV orientation but are located to the right and left of the central frequency. Both frequencies can lie on the same edge in the spectrum, i.e., both on a rising or both on a falling edge. This allows for the measurement of an average frequency deviation between the respective average actual frequencies of the alternating magnetic field and the two peaks (or dips) in the fluorescence spectrum, from which the drift R.416443 can be determined.
[0023] - 4 -
[0024] D can be determined. Or the frequencies lie on different edges in the spectrum, i.e., one on a rising edge and the other on a falling edge. This allows a frequency difference between two peaks in the fluorescence spectrum to be measured, from which the external magnetic field B can be determined.
[0025] In both cases, the different interactions of the NV center with changes in frequency or temperature, on the one hand, and changes in the magnetic field, on the other, are exploited. 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 change in frequency or temperature, or more generally, a drift, shifts the resonance lines in the same direction. It should be noted that a "resonance line" in the spectrum is not a sharp line, but rather has a peak shape (see Fig. 1). The excitation frequency is shifted towards the crest of the resonance line. Conveniently, the frequency corresponds to the point of maximum slope in the spectrum and thus to the sensitivity maximum. This ensures that only the points with the highest information content are sampled, while potential measurement points in between are not measured.This has the advantage that the useful signal can be measured fully scaled (i.e., with maximum amplitude).
[0026] In detail, in step 1) an NV quantum system, which has a plurality of NV centers, where each NV center of the plurality of NV centers is aligned in one of four possible NV orientations, is excited by a pulsed excitation light in order to bring the NV quantum system into the spin state |m s = 0> to initialize.
[0027] In step 2), the NV quantum system is excited at a first time point by an alternating magnetic field which simultaneously has a first and a second frequency, whereby NV centers that are in a first measurement state are stimulated by the alternating magnetic field R.416443
[0028] - 5 -
[0029] with the first frequency into the spin state |m s= -1 > are converted, and where NV centers that are in a second measurement state are converted into the spin state |m by an alternating magnetic field with the second frequency s = +1> are converted. As described previously, a resonance line to the right and left of the central frequency, belonging to the same NV orientation, is excited simultaneously. The first measurement state comprises a primary hyperfine level of one of the four possible NV orientations, and the second measurement state comprises a secondary hyperfine level of the first NV orientation. The primary and secondary hyperfine levels can be the same or different hyperfine levels.
[0030] A state referred to as a "measurement state" within the context of this disclosure is always characterized by a specific combination of a hyperfine level and an NV orientation, or rather, the NV center is located within it. It should be emphasized that the terms "primary," "secondary," etc., in connection with hyperfine levels and NV orientations serve only for conceptual distinction and can refer to the same hyperfine level or the same NV orientation, or to different hyperfine levels or different NV orientations. Accordingly, the first and second measurement states can be the same if the primary and secondary hyperfine levels are the same, or different if the primary and secondary hyperfine levels are different.
[0031] In step 3), a measurement signal emanating from the NV quantum system is acquired. This measurement signal is formed by the sum of the fluorescence caused by the first and second frequencies. In step 4), a measured value is then determined from, or depending on, the measurement signal. The measured value can, in particular, be a frequency difference (and thus an external magnetic field along the NV orientation of the measured state) or a mean frequency deviation between the mean actual frequencies of the magnetic field.
[0032] - 6 -
[0033] Alternating field and the resonance line or peak or dip in the fluorescence spectrum are characterized, depending on the type of excitation and evaluation, as described below.
[0034] In step 5a), a frequency difference between a first and a second peak in the fluorescence spectrum, in which the fluorescence intensity is plotted against the frequency, is determined as a function of the measured value. This is achieved when the first and second frequencies are chosen such that one lies on a falling edge of the first peak and the other on a rising edge of the second peak. With this edge selection, a linear frequency shift (i.e., drift-induced) leads to an opposing change in the individual signals and thus to no change in the sum signal (=measurement signal). This means that changes in the frequency deviation between different measurements do not affect the measurement signal, and only changes in the external magnetic field between different measurements affect the measurement signal. Therefore, changes in the external magnetic field can be measured.
[0035] Alternatively or additionally, in step 5b), a mean frequency deviation or drift between the mean actual frequency of the alternating magnetic field and the first and second peaks / dip, respectively, is determined as a function of the measured value, provided that the first and second frequencies are chosen such that they both lie on a falling or rising edge of different first and second peaks. In other words, an average value is determined from a) the deviation between the mean actual frequency of the alternating magnetic field and the first peak, and b) the deviation between the mean actual frequency of the alternating magnetic field and the second peak. The mean actual frequency of the alternating magnetic field for an NV orientation m and a first peak / dip a is defined as
[0036] f > fma- + fma+
[0037] JMW,maR.416443
[0038] - 7 -
[0039] where the actual microwave frequencies f ma -,fma+ lie symmetrically to the mean actual frequency on a falling edge (-) and on a rising edge (+) of the peak. Each of f ma ,fma+ represents the first frequency, and each of f m b-,fmb+ represents the second frequency.
[0040] With this edge selection, a frequency splitting (i.e., field-induced) leads to an opposing change in the individual signals and thus to no change in the sum signal (=measurement signal). This means that changes in the external magnetic field between different measurements do not affect the measurement signal, and only changes in frequency deviation between different measurements affect the measurement signal. Therefore, changes in frequency deviation can be measured.
[0041] In embodiments of the invention, the method can be a pulsed ODMR measurement.
[0042] A special feature of the invention is therefore the simultaneous use in the fluorescence spectrum of the edges of both electron spin transitions |m s = 0> — > |m s = -1>, |m s = 0> — > |m s= +1>, which are associated with an NV orientation or crystal axis of the diamond (see description of the figures). By cleverly selecting these measurement points, both the magnetic field signal (splitting) and the temperature / drift signal (shift) can be orthogonally encoded into the pulse modulation, so that both effects can be considered separately and quantitatively after demodulation. The splitting (=B) can be determined using one demodulation sequence or by mutually calculating the obtained signal values, and the shift (=D) using another demodulation sequence. This has the advantage that no information for the actual magnetic field measurement (splitting) is lost and the sensitivity of the sensor is therefore not negatively affected. R.416443
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[0044] 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.
[0045] According to embodiments of the invention, steps 2) and 5a) or 5b) are additionally carried out for at least one further NV orientation of the four possible NV orientations.
[0046] According to one embodiment, step 2) at the first time point additionally comprises exciting the NV quantum system by an alternating magnetic field which additionally has a third and a fourth frequency, wherein NV centers that are in a third measurement state are brought into the spin state |m by the alternating magnetic field with the third frequency. s = -1> are converted, and NV centers that are in a fourth measurement state are converted into the spin state |m by an alternating magnetic field with the fourth frequency. s = +1> will be transferred.
[0047] The third measurement state comprises a primary hyperfine level of a second NV orientation of the four possible NV orientations, and the fourth measurement state comprises a secondary hyperfine level of the second NV orientation of the four possible NV orientations, where the second NV orientation differs from the first NV orientation.
[0048] The primary hyperfine level of the first NV orientation may coincide with the primary hyperfine level of the second NV orientation, but it does not have to.
[0049] The third measurement state is not identical to the first measurement state, and the fourth measurement state is not identical to the second measurement state. R.416443
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[0051] In step 5a), a frequency difference between a third peak and a fourth peak in the fluorescence spectrum, in which the fluorescence intensity is plotted against the frequency, is additionally determined as a function of the measured value, wherein the third and the fourth frequencies are chosen such that one lies on a falling edge of the third peak and the other on a rising edge of the fourth peak in the fluorescence spectrum, in which the fluorescence intensity is plotted against the frequency.
[0052] In step 5b), an additional mean frequency deviation is determined between a mean actual frequency of the alternating magnetic field and the third or fourth peak, respectively, whereby the third and fourth frequencies are chosen such that both lie on a falling or both on a rising edge of different third and fourth peaks.
[0053] According to a further embodiment, step 2) at the first time point additionally comprises exciting the NV quantum system by an alternating magnetic field which additionally has a fifth and a sixth frequency, wherein NV centers that are in a fifth measurement state are brought into the spin state |m by the alternating magnetic field with the fifth frequency. s = -1> are converted, and NV centers that are in a sixth measurement state are converted into the spin state |m by an alternating magnetic field with the sixth frequency. s= +1> will be transferred.
[0054] The fifth measurement state comprises a primary hyperfine level of a third NV orientation of the four possible NV orientations, and the sixth measurement state comprises a secondary hyperfine level of the third NV orientation, the third NV orientation being different from the first and second NV orientations. R.416443
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[0056] The fifth measurement state is not identical to the third measurement state and not identical to the first measurement state, and the sixth measurement state is not identical to the fourth measurement state and not identical to the second measurement state.
[0057] In step 5a), a frequency difference between a fifth peak and a sixth peak in the fluorescence spectrum, in which the fluorescence intensity is plotted against the frequency, is additionally determined as a function of the measured value, wherein the fifth and the sixth frequencies are chosen such that one lies on a falling edge of the fifth peak and the other on a rising edge of the sixth peak in the fluorescence spectrum, in which the fluorescence intensity is plotted against the frequency.
[0058] In step 5b), an additional mean frequency deviation is determined between a mean actual frequency of the alternating magnetic field and the fifth or sixth peak, respectively, whereby the fifth and sixth frequencies are chosen such that both lie on a falling or both on a rising edge of different fifth and sixth peaks.
[0059] According to a further embodiment, step 2) at the first time point additionally comprises exciting the NV quantum system by an alternating magnetic field which additionally has a seventh and an eighth frequency, wherein NV centers that are in a seventh measurement state are brought into the spin state |m by the alternating magnetic field with the seventh frequency. s = -1> are converted, and NV centers that are in an eighth measurement state are converted into the spin state |m by an alternating magnetic field with the eighth frequency. s = +1> will be transferred.
[0060] The seventh measurement state comprises a primary hyperfine level of a fourth NV orientation of the four possible NV orientations and the eighth R.416443
[0061] - 11 -
[0062] The measurement state includes a secondary hyperfine level of the fourth NV orientation, with the fourth NV orientation being distinct from the first, second, and third NV orientations.
[0063] The seventh measurement state is not identical to the fifth measurement state, nor to the third measurement state, nor to the first measurement state, and the eighth measurement state is not identical to the sixth measurement state, nor to the fourth measurement state, nor to the second measurement state.
[0064] In step 5a), a frequency difference between a seventh peak and an eighth peak in the fluorescence spectrum, in which the fluorescence intensity is plotted against the frequency, is additionally determined as a function of the measured value, wherein the seventh and the eighth frequencies are chosen such that one lies on a falling edge of the seventh peak and the other on a rising edge of the eighth peak in the fluorescence spectrum, in which the fluorescence intensity is plotted against the frequency.
[0065] In step 5b), an additional mean frequency deviation is determined between a mean actual frequency of the alternating magnetic field and the seventh or eighth peak, respectively, whereby the seventh and eighth frequencies are chosen such that both lie on a falling or both on a rising edge of different seventh and eighth peaks.
[0066] In particular, up to four NV orientations can be measured simultaneously by exciting a resonance line to the right and left of the center frequency for each NV orientation. Measuring three orientations is expediently sufficient, as this allows both the strength and direction of the external magnetic field to be determined. R.416443
[0067] - 12 -
[0068] Alternatively or in addition to multiple NV orientations, multiple hyperfine levels of the same NV orientation can also be used simultaneously (e.g., up to six for nitrogen). 14 N, three each per transition to the spin state |m s = -1> and |m s = +1>) are measured by exciting a resonance line to the right and left of the central frequency for each hyperfine level. Measuring two or more hyperfine levels results in a better signal-to-noise ratio.
[0069] According to one embodiment, at the first time point, for at least one selected NV orientation of the four possible NV orientations, NV centers located in two further hyperfine levels (i.e., a total of four) are excited.
[0070] Step 2) comprises, for each of the at least one selected NV orientation, in addition to the first time point, an excitation of the NV quantum system by an alternating magnetic field which additionally has two further frequencies, wherein NV centers which are located in a tertiary hyperfine level of the selected NV orientation are brought into the spin state |m by the alternating magnetic field with one of the first of the two further frequencies. s = -1> are converted, and wherein NV centers located in a quaternary hyperfine level of the selected NV orientation are converted into the spin state |m by the alternating magnetic field with a second of the two further frequencies. s = +1> will be transferred.
[0071] Step 5a) additionally includes determining a frequency difference between a first additional peak and a second additional peak in the fluorescence spectrum, in which the fluorescence intensity is plotted against the frequency, as a function of the measured value, wherein the first and second of the two additional frequencies are chosen such that one lies on a falling edge of the first additional peak and the other on a rising edge of the second additional peak. R.416443
[0072] - 13 -
[0073] Step 5b) additionally includes determining a mean frequency deviation between a mean actual frequency of the alternating magnetic field and the first further or the second further peak in the fluorescence spectrum as a function of the measured value, wherein the first of the two further frequencies and the second of the two further frequencies are chosen such that both lie on a falling or both on a rising edge of different first further and second further peaks in the fluorescence spectrum.
[0074] According to another embodiment, at the first time point, for at least one selected NV orientation of the four possible NV orientations, NV centers located in two further hyperfine levels (i.e., a total of six) are excited.
[0075] Step 2) comprises, for each of the at least one selected NV orientation, in addition to the first time point, an excitation of the NV quantum system by an alternating magnetic field which additionally has two further frequencies, wherein NV centers which are located in a quinary hyperfine level of the selected NV orientation are brought into the spin state |m by the alternating magnetic field with one of the first of the two further frequencies. s = -1> are converted, and wherein NV centers located in a sexter hyperfine level of the selected NV orientation are converted into the spin state |m by the alternating magnetic field with a second of the two further frequencies. s = +1> will be transferred.
[0076] Step 5a) additionally includes determining a frequency difference between a third further peak and a fourth further peak in the fluorescence spectrum, in which the fluorescence intensity is plotted against the frequency, as a function of the measured value, wherein the first of the two further frequencies and the second of the two further frequencies are chosen such that a falling edge of the R.416443
[0077] - 14 -
[0078] the third further peak and the other on a rising flank of the fourth further peak.
[0079] Step 5b) additionally includes determining a mean frequency deviation between a mean actual frequency of the alternating magnetic field and the third or fourth peak in the fluorescence spectrum as a function of the measured value, wherein the first and second frequencies are chosen such that both lie on a falling or rising edge of different peaks of the third and fourth peaks in the fluorescence spectrum.
[0080] As mentioned, there can be two, four, or six (using the example of 14 Peaks belonging to hyperfine levels for each NV orientation are measured.
[0081] According to one embodiment, in step 2), the frequencies are determined by rows or columns of a matrix with orthogonal sequences, e.g., a Walsh matrix W, wherein a first value of a matrix element of the row or column defines a rising edge and a second value of the matrix element of the row or column defines a falling edge. This allows a desired measurement scheme for determining frequency intervals (and thus the magnetic field) and / or mean frequency deviations (and thus the drift) to be generated very easily.
[0082] According to one embodiment, a Walsh matrix W(8) is used. This allows six measurement states to be measured, corresponding on the one hand to three NV orientations and on the other hand to the three hyperfine levels of nitrogen. 14 N is sufficient.
[0083] According to one embodiment, step 4) comprises determining the measured value from the measurement signals by demodulating the measurement signal with the matrix containing orthogonal sequences, in particular the Walsh matrix W. The steps for modulating and demodulating signals using R.416443
[0084] - 15 -
[0085] Orthogonal functions, especially Walsh functions or Walsh matrices, are well known in the prior art from signal processing and will not be discussed in detail here.
[0086] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.
[0087] The invention is schematically illustrated in the drawing using exemplary embodiments and is described below with reference to the drawing.
[0088] Brief description of the drawings
[0089] Figure 1 shows a simplified fluorescence spectrum of an NV quantum system with two transitions m s = 0>— >|m s = -1> and m s = 0>— >|m s = +1>, where the fluorescence intensity is plotted against the frequency of the alternating magnetic field.
[0090] Figure 2 shows another exemplary fluorescence spectrum of an NV quantum system with four NV orientations and three hyperfine levels per transition, where the fluorescence intensity is plotted against the frequency of the alternating magnetic field.
[0091] Figure 3 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.
[0092] Figure 4 schematically shows a field generation device, as it can be used in embodiments of the invention, in a block diagram. R.416443
[0093] - 16 -
[0094] Figure 5 shows an exemplary measurement based on Walsh sequences for a measurement according to an embodiment of the invention.
[0095] Figure 6 shows frequencies contained in the fluorescence spectrum, similar to those in Fig. 1.
[0096] embodiment(s) of the invention
[0097] Diamond nitrogen vacancy magnetometers are based on the detection of magnetic resonances of 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 describes a pair consisting of a nitrogen atom, which replaces a single carbon atom in the diamond lattice, and an adjacent vacancy in the lattice. If the NV center is optically excited in its normal state without a magnetic field, for example, by irradiating it with a pump laser beam of a suitable wavelength (in this case, 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 ms If the value is ±1 larger, continuous excitation pumping ensures that the NV centers are mostly in the spin state |m s = 0> become polarized.
[0098] Between the |m s = 0> and |m s There is an energy difference between the spin states in the ground state, which in this case is around 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, because the spin-polarized electrons are disturbed by the microwave field from |m s = 0> in the |m s = ±1>-ground state can be raised and from there into the R.416443 by the pump light.
[0099] - 17 -
[0100] |m 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.
[0101] 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. Figure 1 shows a schematic section of a spectrum that can be recorded during an optically detected magnetic resonance (ODMR) measurement. This so-called ODMR spectrum shows the intensity I of the NV fluorescence as a function of the frequency / wir of the microwave excitation for an NV orientation m. The spectrum shows two dips shifted towards the center frequency of 2.87 GHz and at f ma and
[0102]
[0103] lie. For example, / ma during a transition |m s = 0> — > |m s = +1> and magnetic quantum number rni=-1, / m "during a transition |m s = 0> — > |m s = -1> and magnetic quantum number mp-1.
[0104] Each of these dips consists of 14 N in a high resolution from three hyperfine dips (see Fig. 2), since nitrogen 14 N has three nuclear spin levels and therefore splits each electron spin level into three sublevels. The interaction of the electron spin with the nuclear spin further splits the resonance lines, with the NV centers being characterized by 14 N-lon shows three hyperfine lines per resonance line in the spectrum.
[0105] Since the NV center in the single-crystal diamond lattice has four possible NV orientations 01 to 04, in the presence of a directed R.416443
[0106] - 18 -
[0107] The external magnetic field B causes the various NV centers present in the crystal to react differently to the external magnetic field depending on their orientation. In zero field conditions, i.e., without an applied magnetic field or at very small fields, the spin transitions of all four NV orientations 01 to 04 are excited at essentially the same microwave frequency, so that the observed resonance corresponds to the sum of all NV 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. Therefore, if the existing magnetic field has different field components in all four possible NV orientations or diamond crystal axes, four separate resonances are obtained when tuning the microwave frequency.
[0108] Pairs 01 to 04 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 associated magnetic field component. For the magnetic field B m in the NV orientation, approximately:
[0109] “(fmb fma) Bm « - (1)
[0110]
[0111] 2ye
[0112] with the gyromagnetic ratio of the electron y e / 2TT = 28 GHz / T.
[0113] If the applied external directed magnetic field is increased, the two minima of a pair move further apart. The magnetic field B can therefore be determined from the frequency difference fmb-fma between a first peak and a second peak in the fluorescence spectrum, in which the fluorescence intensity is plotted against the frequency. m determine.
[0114] 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 corresponding frequency shift of the associated fluorescence minima to lower frequencies. R.416443
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[0116] Figure 2 shows a corresponding exemplary resonance spectrum under the influence of an external directed magnetic field, where the fluorine intensity I on the y-axis is plotted against the microwave frequency f in MHz on the x-axis. Eight times three fluorescence minima are visible, with the resonance lines in four spatial directions 01 to 04, each consisting of two Zeeman lines (one on the right in each direction). s = 0>— >|m s = +1>) and left (|m s = 0>— >|m s = -1>) from the center) and three hyperfine lines each (for 14N). From such a spectrum, both the magnetic field strength and the direction of the external magnetic field can be uniquely determined.
[0117] 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 across the four possible NV orientations will be approximately equally distributed in a measurement range, so that all transitions in the spectrum can be observed.
[0118] Figure 3 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.
[0119] 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.
[0120] The field-generating device 2 is configured to generate an electromagnetic field 3, in particular a high-frequency field (HF field), and more specifically a microwave field, and is shown in more detail in Fig. 4. R.416443
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[0122] 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.
[0123] The measurement signal 5 emanating from the NV quantum system 4 is, in its various configurations, a fluorescence signal or light signal.
[0124] Accordingly, the measuring device 6 can, for example, include one or more photodiodes or a photodiode measuring arrangement.
[0125] The computing unit 8 is designed to evaluate the raw signal 7 and to control the field generation unit 2.
[0126] Figure 4 shows a schematic representation of a field generation device 2.
[0127] The field generation device 2 includes a local oscillator 21, which is designed and configured to generate a fundamental frequency f0 of, for example, 2.87 GHz. Furthermore, the field generation device 2 includes a baseband frequency generator, which is designed and configured to generate a variable baseband frequency f. BB generate the fundamental frequency f0 and the baseband frequency f BBare mixed in a mixer 23 to the excitation frequency fw, for example according to fuw= fo+ f B B or fuw = fo- f B B.
[0128] The fundamental frequency f0 usually remains unchanged, while the ODMR measurement is based on the variation of f BB This has been done.
[0129] However, it has been shown that the fundamental frequency f0 of the local oscillator 21 is temporally unstable. This is caused, for example, by a frequency error f. e As described, the following results for the faulty excitation frequency:
[0130] fttW = fo + fßB + fe (2)
[0131] First, the frequency f is determined. ma and then the frequency
[0132]
[0133] measured (or in reverse chronological order), the local oscillator 21 has the frequency error / in the first measurement. e ( / =1) and at the second R.416443
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[0135] Measurement / e ( / =2). When calculating the frequency difference fmb -f ma This results from the standard deviation o f e of the uncorrelated error signal f in the mean of the errors ^2o f e. The frequency error f can be reduced by using a high-quality local oscillator 21 with lower phase noise, but this incurs excessive costs.
[0136] However, if, according to embodiments of the invention, the frequencies f maIf fma and fmb are measured simultaneously, the influence of the frequency error f is almost completely eliminated when calculating the B-field using equation (1) above. In real devices, the slope corresponding to the frequency fma usually differs from the slope corresponding to the frequency fmb. Under these circumstances, the frequency error f is not completely eliminated. However, there are various ways to align the slopes, for example, by adjusting the microwave power.
[0137] For the simultaneous measurement of f maThe microwave frequency tw.e is first modulated with orthogonal sequences. Walsh sequences are an example of orthogonal sequences. Figure 5 shows a rough schematic of a process in which the measurement is performed with eight modulation steps. The representation essentially corresponds to that in Fig. 1, with the modulation steps j plotted on a second y-axis to the right, from bottom to top. It can be seen that at the frequency f ma The measurement is taken first four times on the falling edge (matrix element -1) and then four times on the rising edge (matrix element +1). At the frequency f m b is the sequence rising — > falling — > rising — > falling — > falling — > rising — > falling — > rising.
[0138] For example, in a first modulation step, the frequencies f are simultaneously ma - fuw and fmb + Ay generates, in a second modulation step the frequencies f ma - bf w and fm b - f etc. The Walsh sequence W(8) shown, with eight modulation steps, has eight mutually orthogonal sequences. These can be used to create the R.416443
[0139] Frequencies and thus external magnetic fields of three hyperfine resonances or three NV orientations (2 3 =8) to measure using eight measurement states.
[0140] Eliminating the frequency error f e This works, for example, if the frequency pairs f ma and f mb The following are assigned to the orthogonal sequences. To represent the assignments, the Walsh matrix W(8) is first defined as a combination of eight Walsh vectors Wk(8) with k sign changes as follows:
[0141] r^o (8)i
[0142] 1 1 1 1 1 1 1 1 - 1 1 1 1 -1 -1 -1 -1 W4(8)
[0143] 1 1 -1 -1 -1 -1 1 1 w2(8)
[0144] 1 1 -1 -1 W3(8)
[0145] IV(8) = -1 -1
[0146] 1 -1 -1 1 1 -1 W4(8)
[0147] 1 -1 -1 1 -1 1 W5(8)
[0148] 1 -1 1 -1 -1 1 W6(8)
[0149] -1 -1 1 -1 1 -1
[0150]
[0151] W7(8).
[0152] One possible assignment for the different NV orientations designated m, o, p, q is shown below, purely as an example:
[0153] NV frequency 1 Walsh vector frequency 2 Walsh orientation vector 0 fm=o,a W0(8) fm=o,b W7(8) P fm=p,a Wi(8) fm=p,b W6(8) q fm=q,a W2(8) fm=q,b W5(8)
[0154]
[0155] r fm=r,a W3(8) fm=r,b W4(8) Here, each frequency corresponds to a measurement state and the j-th element of the Walsh vectors W to the y-th simultaneous measurement.
[0156] Another example of a possible assignment is as follows.
[0157] NV - Frequency 1 Walsh vector Frequency 2 Walsh - Orientation Vector 0 fm=o,a W0(8) fm=o,b Wi(8) P fm=p,a W2(8) fm=p,b W3(8) q fm=q,a W4(8) fm=q,b W5(8)
[0158]
[0159] r fm=r,a W6(8) fm=r,b W7(8) Here, each frequency corresponds to a measurement state and the j-th element of the Walsh vectors W to the y-th simultaneous measurement.R.416443
[0160] - 23 -
[0161] The following should be noted:
[0162] The assignment of NV orientations o, p, q, r to the rows in the tables above is arbitrary.
[0163] The negative version of the Walsh matrix, -W(8), can also be used.
[0164] Frequency 1 and frequency 2 can each be arbitrarily interchanged.
[0165] It is also possible to read out fewer than four NV orientations. In this case, the corresponding microwave frequency is not generated. Thus, the required microwave excitation power is reduced.
[0166] Instead of the Walsh vectors Wi(8) to W?(8), all Walsh vectors can also be permuted. A permuted version of Wi(8) would be, for example,
[0167] ^i, rot i(8) = [-1 1 1 1 1 -1 -1 -1]
[0168] The scheme shown refers to the Walsh matrix W(2”) of order 3. This scheme can be analogously applied to a Walsh matrix of a different order n=2, 4, 5,... In the case n=2, it would then only be possible to measure one or two NV orientations. In the case n>3, when using all four NV orientations, not all orthogonal sequences are required.
[0169] Figure 6 shows a simplified ODMR spectrum based on Figure 1, which serves below to illustrate embodiments of the invention. The spectrum again shows the intensity I of the NV fluorescence as a function of the frequency / wir of the microwave excitation, with the two dips (or peaks) at f ma and f mb to center frequency
[0170] f zfs = 2.87 GHz shifted. R.416443
[0171] - 24 -
[0172] The mean microwave frequency, or mean actual frequency of the alternating magnetic field, is defined as
[0173] f > fma- T fma+
[0174] jMW,ma 2
[0175] The target values for the microwave frequencies are selected from operating points in the ODMR spectrum where the slope S is at its maximum. For simplicity, the fluorescence intensity is defined as Io at all operating points.
[0176] The actual microwave frequencies f ma -,fma+ around the frequency f ma deviate from the operating points to
[0177] - a tracking error f O ff S , m a of the NV orientation m
[0178] - the frequency error / e , which has the same influence on all NV orientations;
[0179] - the frequency f, m , which is created by the signal to be measured in NV orientation m.
[0180] The resonance / ma associated tracking errors f O ff S , m a usually differs from that for resonance
[0181]
[0182] associated tracking error f O fß,mb. Since the correction of the tracking error takes place at the end of a Walsh sequence (i.e., after a measurement sequence, when the drift has been determined), f O ff S , m a and f Offi,mb remains unchanged for all steps of a Walsh sequence.
[0183] The frequency error f e is identical for the frequencies fna,fmb, since f e As shown in equation (1), the microwave frequency fuw is "shifted" by a frequency-independent value. The signal frequency shift f s The frequency error f has opposite signs for fma and fmb. e and the frequency f s , m vary with each step j of the Walsh sequence, which is why they are referred to below as / e ( / ) and
[0184]
[0185] R.416443
[0186] Assuming a linear model around the intensity I o This results from the generation of the microwave frequency f ma . for the measured intensity of NV orientation m
[0187] A
[0188]
[0189] na-C / ) 4 + ( Zoffs, ma T Ze( / )) ^* 4 4ffs,ma Is,mff) T 4 C / )-
[0190] Similarly, the following results are obtained for the remaining frequencies:
[0191] Ima+(f) 4 ( Zoffs, ma T fs,m(j) T Ze( / ))^* 4 T 4ffs,ma T Is,mff) Ie(f)
[0192] 4 T ( Zoffs, mb T Ze( / )) ^* 4 4ffs,mb T Is,mff) TZC / ) I
[0193]
[0194] mb+(f) 4 ( Zoffs, mb fs,m(f) T / eC / ) ) $ 4 T 4ffs,mb f (f)
[0195] The frequencies f ma and f"b, from which the magnetic field B is derived m The values that can be determined can then be calculated accordingly:
[0196] f _ r Ana+( / ) Ima-fD _ f 4ffs,ma + Ie(f) Jma / MW,ma / MW,ma
[0197] c > c, Anb + C / ) — Anb-C / ) > „ fffs,mb Ie(f) J
[0198]
[0199] mb JMW,mb + - - JMW,mb "r c
[0200] To calculate the magnetic field, a frequency offset f must be used. H It should be considered that resonant frequencies of different hyperfine sub-ensembles can be used. Thus, the magnetic field B is given by... m in the NV orientation m
[0201] “ _ Zmb fma ZHFS “m 2 Xe 1 I. > - Ioffs,mb 4ffs,ma 24, mO) n I JMW,mb _ / MW,ma 7HFS “> ö (5)
[0202]
[0203] 2 / e \
[0204] Except for Term I O ff S , m b - I O ff S , ma - which is determined below, all variables are known in the formula above. R.416443
[0205] - 26 -
[0206] To demonstrate the influence of the frequency error f e The modulation scheme shown here is omitted; for simplification, the Walsh matrix of order n=2 (i.e., 2) will be used in the following. 2=4). The calculation is performed accordingly for higher-order Walsh matrices.
[0207] 1 1 1 1 ' [W0(4)i
[0208] -1 -1 WA4)
[0209] -1 1 W2(4)
[0210] Ll -i
[0211]
[0212] 1 -1- LW3(4)J
[0213] The channel assignment is selected to
[0214] NV - Frequency 1 Walsh vector Frequency 2 Walsh - Orientation vector 7M=1 fl.a W0(4) fl,b W3(4)
[0215]
[0216] m=2 fl,a WT(4) fbb W2(4)
[0217] Each Walsh vector Wk(4) represents a sequence of four frequencies generated sequentially. A "1" in the Walsh vector Wi(4) represents the frequency f. 2a +, where the intensity I 2a + is measured. Simultaneously, the frequencies resulting from the remaining three Walsh vectors are generated.
[0218] Step;=1 Step j=2 Generated frequencies fla+i fla+i flb+i flb+ fla+i fla+if?b-} flb-
[0219] Measured intensity I(f Ilaf^+haf^+hb^+IlbÄV
[0220]
[0221] Step;=3 Step;=4 Generated frequencies fla+i fla-t f?b-} flb+ fla+i fla-t flb+i flb-
[0222] Measured intensity 1(f) / / n (3) + 4,.(3)+ / _-. / ,.(3)+ / / / , (3) haf^+ha ^+hbf^+Ilb-^)
[0223]
[0224] Furthermore, the intensities R.416443
[0225] KD — 4a+ (D + ^2a+ (1) + hb + (1) + hb + (1)
[0226] = 4 + A>ffs,la + 4.1 (1) - 4(1) + 4 + 4ffs,2a + 4.2(1) - 4(1) + 4 + 4ffs,2b — 4,2(1) — 4(1) + 4 + 4ffs,ib — 4.1(1) — 4(1)
[0227]
[0228] = 44 + 4ffs,la + 4ffs,lb + 4ffs,2a + 4ffs,2b - 4 4 (1)
[0229] It should be noted that the intensity changes were eliminated by the components 4,i(l) and 4,2(1).
[0230] 1(2) — 4 + 4ffs,ia + 4,i(2) — 4(2) + 4 + 4ffs,2a + 4,2(2) — 4(2) + 4
[0231] — 4ffs,2b + 4,2(2) + 4(2) + 4 — 4ffs,lb + 4,i(2) + 4(2) 44 " 4ffs,la 4ffs,lb + 4ffs,2a 4ffs,2b " 24.1(2) + 24.2(2)
[0232] 1(3) = 4 + 4ffs,la + 4.1(3) — 4(3) + 4 — 4ffs,2a — 4.2(3) + 4(3) + 4
[0233] — 4ffs,2b + 4,2(3) + 4(3) + 4 + 4ffs,ib — 4.1(3) — 4(3) 44 4" 4ffs,la 3" 4ffs,lb 4ffs,2a 4ffs,2b
[0234] 1(4) - 44 + 4ffs,la - 4ffs,lb - 4ffs,2a + 4ffs,2b + 2 4.1(4) - 24.2(4)
[0235] Decoding is performed by multiplying the measured sum intensities by the Walsh matrix. This yields four signals, Ji to J4.
[0236] 1711 [1(1)1 4 1(2) h 1(3) UJ L / (4)J 164 + 44ffs,la 44ffs,2a - 44(1) + 24.1(2) - 24.1(4) + 24.2(2) + 24.2(4) 44ffs,2b - 44(1) - 24.1(2) + 24, i (4) - 24.2(2) - 24.2(4)
[0237]
[0238] 44ffs,ib - 44(1) - 24,i(2) - 24,! (4) - 24.2(2) + 24.2(4)
[0239] Furthermore, it follows
[0240] L4 -A]
[0241] J3 ~ J2.
[0242] = -164 - 4 ffs,la + 4 ffs,lb - 44.1(2) - 44, i (4) - 44.2(2) + 44.2(4) 41off S ,2b - 4 ffs,2a - 44.1 (2) + 44,! (4) - 44.2 (2) - 44.2 (4)R.416443
[0243] - 28 -
[0244] If we now assume that the measurement signal I s , m Since the external magnetic field m does not change between two steps of the Walsh sequence (because it does not change in the NV orientation), the following applies:
[0245] ,i =,i(2) = 4.1 (4) and 4.2= 4.2(2) = 4.2 (4).
[0246] This results in a simplification.
[0247] J4 Ji _ 16 / Q 4 / o ff s la +4 / o ff s lb 84.1
[0248]
[0249] J3 J2. 4 / o ffs,2b 4 / o ffs,2a 84,2
[0250] Thus, equation (5) for m = 1 can be written as
[0251] 1 ( / 4 - / I + 16 / 0\ #1 — 5 ( 4wiV,lb — / MW,la — ZHFS 1 TT ) (6) 2y e v 45 / and for
[0252]
[0253] m = 2
[0254] ®2 = 7 (f MW, 2b ~ / iviw,2a — / »FS 1 77 ) (?)
[0255]
[0256] 2y e v 45 /
[0257] Since all variables are known from equations (6) and (7), Bi and B2 can be calculated and the frequency error f can be determined. e has no effect on the measurement.
[0258] In addition to the described measurement of the magnetic field B mA drift D can also occur in a corresponding way m are determined depending on a mean frequency deviation between a mean actual frequency fuw.ma or fuw.mb of the alternating magnetic field and the frequency of the first peak / ma or second peaks in the fluorescence spectrum,
[0259]
[0260] / 2 [( / MW,mb fmb)' + ( / MW,ma fma)]-
[0261] Taking into account the equations above, this can be converted into a mean frequency deviation in NV orientation m
[0262]
[0263] V 2 ( / offs,mb fe 0 ) ”l" / offs,ma fe 0 ) )R.416443
[0264] - 29 -
[0265] between the respective real microwave frequencies {f ma + or / ma .) (or the actual frequency of the alternating magnetic field) and the point of maximum slope in the frequency spectrum. The calculation from Ji to J4 is as follows:
[0266] / 4 + Jl 16 / 0+ 4 / offs la +4 / offs lb - 8 / e (1)
[0267] —
[0268]
[0269] h +h 4 / offs, 2a + 4 / offs, 2b - 8 / e (1)
[0270] From this, D m remove immediately.
[0271] In summary:
[0272] For the measurement of the magnetic field B, the selection rule is that its sign should be the same with respect to magnetic field changes 8B and average out with respect to frequency changes 8D. Therefore, the opposite edges are always used to suppress 8D and to have only the component of 8B in the individual measurement.
[0273] For measuring the frequency deviation D, the selection rule is that the sign should be the same for frequency changes 8D and averages out for magnetic field changes 8B. Therefore, the same edges are always used to suppress fluctuations and ensure that only the 8D component is present in each measurement.
[0274] To measure multiple NV orientations, different Walsh sequences can be used for modulation / demodulation.
[0275] Furthermore, the two calculations described from Ji to J4 allow both the magnetic field and the frequency deviation to be determined with the same measurements.
Claims
R.416443 - 30 - Claims 1. Method for evaluating a measurement signal (5) emanating from an NV quantum system (4), wherein the NV quantum system (4) has a plurality of NV centers, wherein each NV center of the plurality of NV centers is oriented in one of four possible NV orientations (01,..., 04), the procedure encompasses the following steps: 1) Excitation of the NV quantum system (4) by a pulsed excitation light (13) to bring the NV quantum system (4) into the spin state |m s = 0> to initialize, 2) at a first time, excitation of the NV quantum system (4) by an alternating magnetic field (3) which simultaneously has a first and a second frequency, whereby NV centers that are in a first measurement state are brought into the spin state |m by the alternating magnetic field (3) with the first frequency s= -1> are converted, and where NV centers that are in a second measurement state are converted into the spin state |m by the alternating magnetic field (3) with the second frequency s = +1> are converted, wherein the first measurement state comprises a primary hyperfine level of a first NV orientation of the four possible NV orientations (01,..., 04) and wherein the second measurement state comprises a secondary hyperfine level of the first NV orientation, 3) Detection of a measurement signal (5) emanating from the NV quantum system (4), 4) Determining a measured value from the measurement signal (5), 5a) Determining a frequency difference between a first peak and a second peak in the fluorescence spectrum, inR.416443 - 31 - in which the fluorescence intensity is plotted against the frequency, as a function of the measured value, wherein the first and second frequencies are chosen such that one lies on a falling edge of the first peak and the other on a rising edge of the second peak, and / or 5b) Determining a mean frequency deviation between a mean actual frequency of the alternating magnetic field (3) and the first or second peak in the fluorescence spectrum as a function of the measured value, wherein the first and second frequencies are chosen such that both lie on a falling or both on a rising edge of different first and second peaks in the fluorescence spectrum.
2. Method according to claim 1, o where step 2) additionally includes: At the first time point, the NV quantum system (4) is excited by an alternating magnetic field (3) which additionally has a third and a fourth frequency, whereby NV centers that are in a third measurement state are brought into the spin state |m by the alternating magnetic field (3) with the third frequency. s = -1> are converted, and wherein NV centers that are in a fourth measurement state are subjected to the alternating magnetic field (3) with the fourth frequency (f ma , f mb ) into the spin state |m s = +1> are converted, wherein the third measurement state comprises a primary hyperfine level of a second NV orientation of the four possible NV orientations (01,..., 04) and the fourth measurement state comprises a secondary hyperfine level of the second NV orientation of the four possible NV orientations (01,..., 04), where the second NV orientation differs from the first NV orientation, where step 5a) additionally includes: R.416443 - 32 - Determining a frequency difference between a third peak and a fourth peak in the fluorescence spectrum, in which the fluorescence intensity is plotted against the frequency, as a function of the measured value, wherein the third and fourth frequencies are chosen such that one lies on a falling edge of the third peak and the other on a rising edge of the fourth peak. o where step 5b) additionally includes: Determining a mean frequency deviation between a mean actual frequency of the alternating magnetic field (3) and the third or fourth peak in the fluorescence spectrum as a function of the measured value, wherein the third and fourth frequencies are chosen such that both lie on a falling or both on a rising edge of different third and fourth peaks in the fluorescence spectrum.
3. Method according to claim 2, o where step 2) additionally includes: At the first time point, the NV quantum system (4) is excited by an alternating magnetic field (3) which additionally has a fifth and a sixth frequency, whereby NV centers that are in a fifth measurement state are brought into the spin state |m by the alternating magnetic field (3) with the fifth frequency. s = -1> are converted, and wherein NV centers that are in a sixth measurement state are converted into the spin state |m by the alternating magnetic field (3) with the sixth frequency s = +1> are converted, wherein the fifth measurement state comprises a primary hyperfine level of a third NV orientation of the four possible NV orientations (01,..., 04) and wherein the sixth measurement state comprises a secondary hyperfine level of the third NV orientation of the four possible NV orientations (01,..., 04), the third NV orientation differs from the first and second NV orientations, where step 5a) additionally includes: R.416443 - 33 - Determining a frequency difference between a fifth peak and a sixth peak in the fluorescence spectrum in which the fluorescence intensity is plotted against the frequency, as a function of the measured value, wherein the fifth and sixth frequencies are chosen such that one lies on a falling edge of the fifth peak and the other on a rising edge of the sixth peak. o where step 5b) additionally includes: Determining a mean frequency deviation between a mean actual frequency of the alternating magnetic field (3) and the fifth or sixth peak in the fluorescence spectrum as a function of the measured value, wherein the fifth and sixth frequencies are chosen such that both lie on a falling or both on a rising edge of different fifth and sixth peaks in the fluorescence spectrum.
4. Method according to claim 3, o where step 2) additionally includes: At the first time point, the NV quantum system (4) is excited by an alternating magnetic field (3) which additionally has a seventh and an eighth frequency, whereby NV centers that are in a seventh measurement state are brought into the spin state |m by the alternating magnetic field (3) with the seventh frequency s= -1> are converted, and where NV centers that are in an eighth measurement state are converted into the spin state |m by the alternating magnetic field (3) with the eighth frequency s = +1> are converted, wherein the seventh measurement state comprises a primary hyperfine level of a fourth NV orientation of the four possible NV orientations (01,..., 04) and wherein the eighth measurement state comprises a secondary hyperfine level of the fourth NV orientation, the fourth NV orientation differs from the first, second and third NV orientations, where step 5a) additionally includes: R.416443 - 34 - Determining a frequency difference between a seventh peak and an eighth peak in the fluorescence spectrum in which the fluorescence intensity is plotted against the frequency, as a function of the measured value, wherein the seventh and eighth frequencies are chosen such that one lies on a falling edge of the seventh peak and the other on a rising edge of the eighth peak, o wherein step 5b) additionally includes: Determining a mean frequency deviation between a mean actual frequency of the alternating magnetic field (3) and the seventh and eighth peaks in the fluorescence spectrum as a function of the measured value, wherein the seventh and eighth frequencies are chosen such that both lie on a falling or both on a rising edge of different seventh and eighth peaks in the fluorescence spectrum.
5. Method according to any one of the preceding claims, wherein at the first time point for at least one selected NV orientation of the four possible NV orientations (01,..., 04) NV centers located in two further hyperfine levels are stimulated, where step 2) additionally includes for each of the at least one selected NV orientation: At the first time point, the NV quantum system (4) is excited by an alternating magnetic field (3), which additionally has two further frequencies, wherein NV centers located in a tertiary hyperfine level of the selected NV orientation are brought into the spin state |m by the alternating magnetic field (3) with a first of the two further frequencies s = -1> be transferred, and wherein NV centers located in a quaternary hyperfine level of the selected NV orientation are brought into the spin state |m by the alternating magnetic field (3) with a second of the two further frequencies s= +1> be transferred,R.416443 - 35 - o where step 5a) additionally includes: Determining a frequency difference between a first additional peak and a second additional peak in the fluorescence spectrum, in which the fluorescence intensity is plotted against the frequency, as a function of the measured value, wherein the first of the two additional frequencies and the second of the two additional frequencies are chosen such that one lies on a falling edge of the first additional peak and the other on a rising edge of the second additional peak. o where step 5b) additionally includes: Determining a mean frequency deviation between a mean actual frequency of the alternating magnetic field (3) and the first further or the second further peak in the fluorescence spectrum as a function of the measured value, wherein the first of the two further frequencies and the second of the two further frequencies are chosen such that both lie on a falling or both on a rising edge of different first further and second further peaks in the fluorescence spectrum.
6. Method according to claim 5, where, at the first time point, for at least one selected NV orientation of the four possible NV orientations (01,..., 04), NV centers located in two further hyperfine levels are stimulated, where step 2) additionally includes for each of the at least one selected NV orientation: At the first time point, the NV quantum system (4) is excited by an alternating magnetic field (3), which also has two additional frequencies, wherein NV centers located in a quinary hyperfine level of the selected NV orientation are brought into the spin state |m by the alternating magnetic field (3) with a first of the two further frequencies s = -1> be transferred, andR.416443 - 36 - wherein NV centers located in a sexter hyperfine level of the selected NV orientation are brought into the spin state |m by the alternating magnetic field (3) with a second of the two further frequencies s = +1> will be transferred o where step 5a) additionally includes: Determining a frequency difference between a third and a fourth peak in the fluorescence spectrum, in which the fluorescence intensity is plotted against the frequency, as a function of the measured value, wherein the first and second frequencies of the two additional peaks are chosen such that one lies on a falling edge of the third peak and the other on a rising edge of the fourth peak. o where step 5b) additionally includes: Determining a mean frequency deviation between a mean actual frequency of the alternating magnetic field (3) and the third or fourth peak in the fluorescence spectrum as a function of the measured value, wherein the first of the two further frequencies and the second of the two further frequencies are chosen such that both lie on a falling or both on a rising edge of different third and fourth peaks in the fluorescence spectrum.
7. Method according to any of the preceding claims, wherein, in carrying out step 2), the frequencies are determined by rows or columns of a matrix with orthogonal sequences, e.g. a Walsh matrix W, wherein a first value of a matrix element of the row or column determines a rising edge and a second value of the matrix element of the row or column determines a falling edge.
8. The method of claim 7, wherein a Walsh matrix W(8) is used. R.416443 - 37 - 9. Method according to claim 7 or 8, wherein step 4) comprises: Determining the measured value from the measurement signals by demodulation with the matrix containing orthogonal sequences.
10. Method according to any of the preceding claims, wherein the electromagnetic field (3) is a microwave field.
11. 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.
12. 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 a pulsed excitation light (13), a field generating device (2) for generating an electromagnetic field (3), wherein the NV quantum system (4) is arranged in the electromagnetic field (3), and a measuring device (6) for detecting the measurement signal (5) emanating from the NV quantum system (4), wherein the device (100) is configured to carry out a method according to one of the preceding claims.