Method and device for detecting magnetic fields

Abstract

The invention relates to a method for detecting magnetic fields (B) by means of a device having at least two magnetometer units (S1, S2) which are based on spin-based quantum systems (110), are arranged in a geometric arrangement with respect to one another and are connected to a signal processing unit (70, 200), wherein the method comprises, for each of the at least two magnetometer units (S1, S2), exciting the spin-based quantum system (110) with excitation light (124) in an excitation period which is completely outside a measurement period in which a magnetic field is detected by the spin-based quantum system (110), and for the at least two magnetometer units (S1, S2), simultaneously exciting the spin-based quantum systems (110) with excitation light (124). The invention also relates to such a device.

Description

[0001] R.414357

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method and device for detecting magnetic fields

[0006] The present invention relates to a method and a device for detecting magnetic fields, for example those generated by a beating heart.

[0007] Background of the invention

[0008] To measure very small magnetic field strengths, optically pumped or NV center-based quantum sensors in diamond are particularly suitable as sensors.

[0009] For such spin-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 is prepared via optical excitation and interaction with a static magnetic field and a dynamic magnetic field, i.e., a microwave field.

[0010] German patent DE 10 2022 204 526 A1 describes a magnetometer that utilizes 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 detected, for example, by optical excitation and frequency-dependent detection of the resulting fluorescence radiation (R.414357).

[0011] - 2 - or can be measured by observing optical properties such as the absorption of light. The magnetic field strength can then be deduced from the measured optical parameters.

[0012] Disclosure of the invention

[0013] According to the invention, a method and a device for detecting magnetic fields, in particular those generated by a beating heart, are proposed, comprising the features of the independent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0014] The invention employs the measure of temporally synchronizing the excitation periods of the quantum systems and separating them from the measurement periods in order to avoid mutual interference in an arrangement of at least two magnetometer units based on spin-based quantum systems.

[0015] When a spin-based magnetometer unit is operated, which includes a light source, particularly a laser light source, to excite the spin-based quantum systems, the power supply to the light source generates a magnetic field that is not insignificant compared to weak magnetic fields, such as those originating from the heart. For a single magnetometer unit, this can be mitigated by pulsed operation of the excitation light, i.e., by separating the operation of the light source (excitation period) from the measurement of the magnetic field (measurement period). However, if several magnetometer units are arranged in a geometric configuration, the light source of one magnetometer unit can significantly interfere with the measurements of other magnetometer units.

[0016] Within the scope of the invention, a synchronization of the individual excitation periods is therefore proposed such that the excitation of the spin-based quantum systems occurs separately in time from the measurement of the magnetic field to be measured, and the excitation of the quantum systems of all magnetometer units always occurs at the same time. This enables the measurement of the magnetic field, e.g., R.414357

[0017] - 3 - by manipulating the ground state of the quantum system with a microwave or microwave pulse train, not affected by the other magnetometer units. A disturbing current for operating the light sources of the other magnetometer units is switched off at this time.

[0018] This synchronization of readout and interference signals can be advantageously applied to all types of interference signals. An interference signal does not necessarily have to originate from a light source, but can also include other current-carrying processes (heating, etc.).

[0019] A device according to the invention for detecting magnetic fields is configured to carry out a method according to the invention.

[0020] In particular, a device according to the invention comprises at least two magnetometer units based on spin-based quantum systems, which are arranged in a geometric arrangement relative to each other and connected to a signal processing unit, wherein the device is configured to arrange for each of the at least two magnetometer units an excitation period in which the spin-based quantum system is excited with excitation light completely outside of a measurement period in which a magnetic field is detected by the spin-based quantum system, and to arrange the excitation periods simultaneously for the at least two magnetometer units.

[0021] It should be noted that a magnetic field to be measured is usually also present outside the measurement period and acts on the quantum system. However, the measurement period is understood to be the period ultimately used for the measurement or the evaluation of the measurement, in particular the period that substantially influences the result, i.e., to more than 50%, preferably more than 66%, 75%, 80%, 85%, 90%, 95%, 99%, preferably completely. If, for example, periods outside the measurement range are also included in the measurement result, they are included to a less than 50%, preferably less than 34%, 25%, 20%, 15%, 10%, 5%, 1%. R.414357

[0022] - 4 -

[0023] According to one embodiment, the same measurement trigger signal is used for the at least two magnetometer units, determining or defining the measurement period in the at least two magnetometer units. The measurement trigger signal can, for example, be output by a central control unit that controls the magnetometer units. Alternatively, the measurement trigger signal can be output by a main or master control unit belonging to one of the at least two magnetometer units and forwarded to sub- or slave control units of the other of the at least two magnetometer units.

[0024] According to one embodiment, the same excitation trigger signal is used for the at least two magnetometer units, determining or defining the excitation period in the at least two magnetometer units. The excitation trigger signal can, for example, be output by a central control unit that controls the magnetometer units. Alternatively, the excitation trigger signal can be output by a main or master control unit belonging to one of the at least two magnetometer units and forwarded to sub- or slave control units of the other of the at least two magnetometer units.

[0025] According to one embodiment, separate, simultaneous measurement trigger signals are used for the at least two magnetometer units. These signals determine the measurement period in the at least two magnetometer units and are derived from a common time base. Each measurement trigger signal can, for example, be output by a control unit belonging to a specific one of the at least two magnetometer units. The time bases or clocks in the control units can be synchronized using known synchronization methods. The start of the measurement periods can be communicated to the control units as a timestamp.

[0026] According to one embodiment, separate simultaneous excitation trigger signals are used for the at least two magnetometer units, which determine the excitation period in the at least two magnetometer units and which are derived from a common time base R.414357

[0027] - 5 - Each excitation trigger signal can, for example, be output by a control unit belonging to one of the at least two magnetometer units. The time bases or clocks in the control units can be synchronized using known synchronization methods. The start of the excitation periods can be communicated to the control units as a timestamp.

[0028] These measures ensure that all magnetometer units in the arrangement have simultaneous measurement and excitation periods.

[0029] The quantum system could, for example, be an NV center in a diamond, where the ground state is a triplet in which (without an external magnetic field) there is an energy difference corresponding to 2.87 GHz between spin equal to 0 on the one hand and spin equal to +1 or -1 on the other. Such NV centers in diamonds could, for example, be used as quantum sensors.

[0030] The quantum system can also include a vapor cell containing a mixture of at least one gaseous alkali metal and at least one gaseous noble gas. Such quantum systems are used particularly in NMR gyroscopes (Nuclear Magnetic Resonance) and evaluate nuclear magnetic resonance signals from atomic nuclei with non-zero magnetic moments. One way to provide a single-axis NMR gyroscope is to use a vapor chamber containing a mixture of an element with non-zero nuclear spin (usually a noble gas, for example, xenon (Xe)) and an alkali metal (such as potassium (K), cesium (Cs), or rubidium (Rb)).

[0031] Diamond nitrogen vacancy (NV) magnetometers are based on reading out the magnetic resonances of specific defect centers in diamond, particularly nitrogen vacancies (NV), which occur as impurities in the carbon lattice of diamond and can also be deliberately introduced. If the NV center is optically excited in its ground state, for example by shining a pump laser beam with a suitable wavelength (in this case in the green wavelength range, e.g., at 532 nm for off-resonance excitation), the R.414357

[0032] - 6 -

[0033] Electrons are excited from the triplet ground state to the excited triplet state and relax, emitting fluorescence light in the red wavelength range at 650–800 nm (637 nm = zero phonon line). Since the probability of non-spin-conserving transitions from the spin state with spin quantum number m sIf the value is greater than ±1, continuous excitation pumping ensures that the NV centers are mostly in the spin state m s = 0 hyperpolarized.

[0034] 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.

[0035] 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 appear in the fluorescence spectrum, the frequency separation of which is proportional to the magnetic field strength of the external magnetic field. In this application, the measurement period is therefore defined by the microwave excitation.

[0036] The magnetic field sensitivity is primarily defined by the minimum resolvable frequency shift and can reach 1 pTA / Hz or less. Since the NV center in single-crystal diamond has four possible orientations within the crystal lattice, the presence of a directed magnetic field results in the NV centers within the crystal reacting differently to the external magnetic field depending on their position. Ideally, this can lead to the appearance of four pairs of fluorescence minima in the spectrum, from which R.414357

[0037] - 7 -

[0038] The shape and relative position of the magnetometers, as well as the magnitude and direction of the external magnetic field, can be unambiguously determined. To enable vectorial magnetic field measurements according to one embodiment, the device includes a means of generating a substantially homogeneous bias magnetic field in the region of the magnetometer units or their sensor media, wherein the bias magnetic fields of different magnetometer units are expediently different. This can be a Helmholtz coil arrangement, with at least the sensor medium located within the Helmholtz coil arrangement (each magnetometer unit has its own bias field). Alternatively, other arrangements can be used, such as a simple coil, an elongated coil, permanent magnet solutions like those in a Hallbach array, etc.

[0039] According to one embodiment, the device is configured to detect a magnetic field strength and direction using each of the at least two magnetometer units, and to determine an effective magnetic field strength and an effective field direction from the magnetic field strengths and field directions detected by the at least two magnetometer units using the signal processing unit, which comprises at least one field vector. Both wireless and wired connections between the sensors and the signal processing unit are provided.

[0040] By using a number of vector magnetometer units in a geometric arrangement and gradiometer interconnection, these magnetometer units have different orientations relative to the magnetic field being measured. Through the gradiometer interconnection, i.e., essentially vector arithmetic of the measured value, the position and strength of the magnetic field exciter (core) can be determined. Since the significantly stronger background field is essentially the same in both magnetometer units (same strength and orientation), it can be eliminated. This eliminates the need for magnetic shielding, making magnetic field measurement possible in everyday environments. A further advantage over classical gradiometer arrangements with one-dimensional magnetometers is the resulting compact design of the gradiometer arrangement, as no distant reference magnetometer is required.

[0041] - 8 - is required. The invention is therefore particularly suitable for the unshielded measurement of weak magnetic fields. Technical details of gradiometer solutions, which can also be used within the scope of the present invention, are disclosed in DE 10 2022 201 690 A1 and are included here.

[0042] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0043] The invention is schematically illustrated in the drawing using exemplary embodiments and is described below with reference to the drawing.

[0044] Brief description of the drawings

[0045] Figure 1 shows in a schematic block view the essential components of an NV center magnetometer as it can be used within the scope of the invention.

[0046] Figure 2 shows a schematic block view of a measurement principle of NV vector gradiometry, as it can be applied in one embodiment of the invention.

[0047] embodiment(s) of the invention

[0048] Figure 1 schematically shows the essential components of an NV center magnetometer, which can be used as a magnetometer unit in a method or device according to a preferred embodiment of the invention. A diamond 110 with nitrogen vacancies (NV) is initially present as a spin-based quantum system and sensor medium. The optical excitation of the NV centers can be achieved by a suitable light source 120, such as an LED or a pump laser. For example, a frequency-doubled Nd:YAG laser or a semiconductor laser in the green range of approximately 510–532 nm is suitable, e.g., at 532 nm for off-resonance operation.

[0049] - 9 -

[0050] Excitation. Alternatively, LEDs in suitable wavelength ranges can also be used. Depending on the arrangement, the light from the light source 120 can be directed into the diamond 110 via suitable optical elements 122 such as mirrors, beam splitters, focusing optics such as lenses, and, if necessary, fiber optic elements. Furthermore, the excitation light can be continuously or pulsedly directed by the laser, so that, for example, time windows for interference-free fluorescence light measurement can be maintained.

[0051] Furthermore, the magnetometer can include a microwave source 150 capable of generating an electromagnetic field in the sensor medium over a bandwidth covering the desired resonance frequency, i.e., in the region of the NV centers of the diamond 110. A microwave resonator structure can be used to distribute the generated microwaves homogeneously over the volume of the measurement area in the diamond. The resonator structure, or microwave source 150, is preferably tuned to the frequency of the electron spin resonances. To enable vector magnetometry, an additional static bias magnetic field 140 is generated. This makes the measurement intrinsically vectorial. For this purpose, different spatial directions in the crystal structure are used. For example, a Helmholtz coil is suitable for generating such a magnetic field 140, in which a substantially homogeneous magnetic field can be generated in a limited area by means of a coil pair.

[0052] The resulting fluorescence light 112 from the diamond 110 can be guided via suitable optical elements 134, such as optical filters, beam splitters, lenses, and / or fiber optic elements, to a first photodetector 130, which is sensitive at least in the range of the fluorescence wavelength. The first photodetector 130 can also be arranged directly on the diamond 110. A second photodetector 132 is arranged such that it can detect at least a portion of the excitation light from the light source 120, which can be coupled out, for example, by a beam splitter, a filter, or a partially transparent element. This detector signal 132 of the excitation light can be used as a reference signal, for example, to modulate the excitation light using a lock-in amplifier R.414357.

[0053] - 10 -

[0054] The aim is to eliminate background signals and isolate the resonance signal of interest. Additionally or alternatively, this reference signal can be used to account for variations in the excitation light. Appropriate circuits 160, such as a preamplifier, a logarithmic amplifier, a lock-in amplifier, signal filters, or others, are therefore provided to obtain the signals from the first and second photodetectors and to preprocess the signals appropriately for further evaluation. Finally, a signal processing unit 170 can evaluate the preprocessed fluorescence signal, for example, with a suitable microcontroller or processor, to obtain the desired parameters of the detected magnetic field from the signal, in particular the magnetic field strength and direction.

[0055] It is understood that such a device may also include other units not shown, such as communication units or interfaces for outputting the measurement results. Such a device can also be advantageously integrated into an ASIC or FPGA.

[0056] To be usable in an everyday environment, magnetic fields that do not originate from desired weak sources should be eliminated from the measurement as far as possible, especially the Earth's magnetic field in the range of 10'. 5 Tesla (a few microteslas). In contrast, the magnetic fields of the heart are in the range of 10-100 times 10- 12 Tesla (Picotesla).

[0057] The elimination of background magnetic fields can be achieved by using a gradiometer arrangement during magnetic field measurement, as described in exemplary embodiments. Gradiometers are generally defined as sensor units capable of detecting not only the field strength but also the field gradient.

[0058] For this purpose, at least two individual magnetometer units S1 and S2 can be used, arranged at spatially different locations. As an example, a sensor unit R.414357 is described below in conjunction with Figure 2.

[0059] - 11 - described, which uses two (or more) NV center magnetometers in a gradiometer arrangement.

[0060] Figure 2 shows a possible geometric arrangement of two NV magnetometer units S1, S2 of a device for detecting magnetic signals according to one embodiment. Furthermore, M denotes a signal source.

[0061] In embodiments of the invention, more than two NV magnetometer units can form a single gradiometer (but at least two). With each additional NV magnetometer unit, the background field can be determined more accurately, and the location and strength of the excitation can be better separated from the background.

[0062] In other embodiments of the invention, two NV magnetometer units can also form a gradiometer, whereby – depending on the number of NV magnetometer units – several gradiometers are formed in total and acquire the signal of interest. An effective measurement signal can then be generated from this, in particular by the signal processing unit, for example by averaging, summation, etc.

[0063] A distance d between two NV magnetometer units S1, S2, ... or more precisely, their sensor media, corresponds to the distance between the locations where magnetic field measurements are performed simultaneously. As long as the distance between the measurement locations is relatively small, it can be assumed that the strength of an additional background magnetic field is approximately the same at both locations. In contrast, the weak magnetic field B of interest will decrease significantly with increasing distance from the magnetic field source M. Furthermore, the different orientation of the excitation's magnetic field (e.g., the heart) allows for a clear separation from the background field, even at small distances.

[0064] The distance d between the sensor heads within a gradiometer unit, i.e., in this case the distance between the two sensor diamonds, can range from mm to several cm, for example between 0.5 cm and 2 cm. For values ​​in R.414357

[0065] - 12 - Good results could be achieved for measuring biomagnetic fields in the picotesla range at these magnitudes. However, as long as sufficient independence of the signals from the background fields is achieved, larger or smaller distances or other gradiometer configurations can also be used, such as sensors arranged side by side. If the distance between the individual sensor heads is too great, the background field may no longer be identical at both locations, especially in the case of local background fields (electrical lines, etc.); conversely, if the distance between the sensor heads is too small, the difference between the field strengths of the magnetic field to be measured may be too small between the two locations.The choice of the appropriate distance between the two sensors of a gradiometer unit is therefore preferably also dependent on the type and orientation of the magnetic field source of interest and on the expected field strength. The distance of the sensor unit from the magnetic field source can also be in the millimeter to centimeter range.

[0066] By positioning two NV magnetometer units at different distances and angles from the source or the heart, the background field can be eliminated or determined using vector arithmetic, thus enabling the identification of the small magnetic field of interest and the characterization of its source (location and orientation). This can be further improved by using a distant magnetometer positioned far enough away that the weak magnetic field of interest has fallen below the detection threshold. With such a configuration, local variations in the background field can be compensated for by the at least two nearby magnetometers. For this purpose, for example, two NV magnetometer units can be stacked one above the other in an axial gradiometer configuration, such that each NV magnetometer unit of a first layer, together with the NV magnetometer unit of a second, underlying layer, forms a gradiometer.The background field can also be determined by placing another NV magnetometer unit at a large distance, e.g. at least 1 m, from the two NV magnetometer units. R.414357.

[0067] - 13 -

[0068] However, it has been shown that in such devices with two or more magnetometer units, the excitation light source 120 or its power supply generates a not insignificant (interference) magnetic field compared to weak magnetic fields, such as those originating from the heart, which can severely disrupt the measurement of other magnetometer units.

[0069] According to embodiments of the invention, a synchronization of the individual excitation periods is proposed such that the excitation of the spin-based quantum systems 110 occurs separately from the measurement of the magnetic field B to be measured, and the excitation of the quantum systems 110 of all magnetometer units S1, S2 always occurs at the same time. Thus, the measurement of the magnetic field B is not affected by the other magnetometer units. A disruptive current for operating the light sources of the other magnetometer units is switched off at this time.

[0070] According to the embodiment described here, one and the same excitation trigger signal 300 is used for the two magnetometer units S1 and S2, which determines the excitation period in the two magnetometer units S1 and S2. The excitation trigger signal 300 is, in this case, a pulse signal or square wave signal, whereby each pulse can switch on the light source 120. The excitation trigger signal 300 is output, for example, by a central control unit 200, which controls the magnetometer units S1 and S2.

[0071] According to the embodiment described here, one and the same measurement trigger signal 301 is used for the two magnetometer units S1 and S2, which determines the measurement period in the at least two magnetometer units. The measurement trigger signal 301 is, in this case, a pulse signal or square wave signal, whereby each pulse can switch on the microwave source 150 or trigger polarization pulses (e.g., so-called TT / 2 pulses). The measurement trigger signal 301 is also output, for example, by the central control unit 200, which controls the magnetometer units S1 and S2.

[0072] An advantageous concept of embodiments of the invention is to vectorially and simultaneously scan the field with several NV magnetometer units from different R.414357

[0073] - 14 -

[0074] Positions are measured. As long as this arrangement is located near the signal source M to be measured, the field of the signal source is measured in different directions by the individual vector sensors. This distribution of the measured field vectors is characteristic and allows conclusions to be drawn about the source regarding its strength, position, and orientation. To detect weak signals compared to the background, the assumption of a homogeneous background field via the geometric arrangement of NV magnetometer units (this is generally assumed here, since the distance between the source of the disturbance and the sensor medium is assumed to be much greater than that of the signal to be measured from the sensor medium) allows the individual field vectors to be calculated, since the vector of the disturbance field can be assumed to be the same, and thus simple vector arithmetic is sufficient to extract the signal vector.Using a geometric arrangement can also compensate for inhomogeneities in the background.

[0075] As shown in Figure 2, the different measurement positions of the NV magnetometer units S1 and S2 determine the field vector in different directions. Since the background field Z1 is the same for both NV magnetometer units, this allows for a calculation of the source's strength and orientation. By measuring the signal / field in different directions (the source's field depends in amplitude and orientation on the position of the individual sensor relative to the source), background noise can be further suppressed (fluctuations orthogonal to the measurement signal are suppressed). This allows for noise suppression superior to the conventional gradiometer approach.

[0076] For example, M1 to M2 are at least one magnetic field component and Z1 to Z2 are at least one disturbance component (e.g., the Earth's magnetic field), which can be static or time-varying. Corresponding NV magnetometer units S1 to S2 measure resulting components R1 to R2, which include the disturbance signal. NV magnetometer unit S1 measures component R1, consisting of the first disturbance Z1 and signal M1, at the location of S1, and NV magnetometer unit S2 measures component R2, consisting of the second disturbance Z2 and signal M2, at the location of S2, and so on. From this, R.414357 can be calculated.

[0077] - 15 - A signal insensitive to interference components can be determined using vector arithmetic. An evaluation can proceed as follows:

[0078] Two vector-valued signals, R1 and R2, are measured. These contain signal components M1 and MT, as well as noise components Z1 and Z2 = Z1, which are identical across the measurement ranges. The gradiometer measurement signal is then calculated as follows:

[0079] As equation (1) describes, the signal no longer contains any interference components, provided these are uniform across the measurement ranges. Furthermore, the measurement signal is vectorial, thus allowing, for example, the assignment of direction ("Where does the signal come from?"), the differentiation of different signals, and the correlation of multiple signals from different sensors in an arrangement (imaging technique).

[0080] The result in equation (1) can be expressed in terms of a magnitude and a direction. This is particularly advantageous when the source lies between the magnetometer units (or in a plane passing through the midpoint of the two) and thus the magnetic field is opposite in direction.

[0081] By using three or more magnetometer units (geometric arrangement), a system of equations can be set up that allows the individual magnetic fields at the magnetometer units to be determined.

Claims

R.414357 - 16 - Claims 1. Method for detecting magnetic fields (B) by means of a device comprising at least two magnetometer units (S1, S2) based on spin-based quantum systems (110), which are arranged in a geometric arrangement relative to each other and connected to a signal processing unit (170, 200), wherein the method comprises: for each of the at least two magnetometer units (S1, S2), excitation of the spin-based quantum system (110) with excitation light (124) in an excitation period which lies completely outside of a measurement period in which a magnetic field is detected by the spin-based quantum system (110), and for the at least two magnetometer units (S1, S2), simultaneous excitation of the spin-based quantum systems (110) with excitation light (124).

2. Method according to claim 1, wherein one and the same measurement trigger signal (301) is used for the at least two magnetometer units (S1, S2), which determines the measurement period in the at least two magnetometer units (S1, S2).

3. Method according to claim 1, wherein separate simultaneous measurement trigger signals are used for the at least two magnetometer units (S1, S2), which determine the measurement period in the at least two magnetometer units (S1, S2) and which are derived from a common time base.

4. Method according to one of the preceding claims, wherein one and the same excitation trigger signal (300) is used for the at least two magnetometer units (S1, S2), which determines the excitation period in the at least two magnetometer units (S1, S2). R.414357 - 17 - 5. Method according to any one of claims 1 to 3, wherein separate simultaneous excitation trigger signals are used for the at least two magnetometer units (S1 , S2), which determine the excitation period in the at least two magnetometer units (S1 , S2) and which are derived from a common time base.

6. Device for detecting magnetic fields (B), comprising at least two magnetometer units (S1, S2) based on spin-based quantum systems (110), which are arranged in a geometric arrangement relative to each other and connected to a signal processing unit (170, 200), wherein the device is configured to carry out a method according to one of the preceding claims.

7. Device according to claim 6, which is configured to detect a magnetic field strength (R1 , R2) and field direction (R1 , R2) by means of each of the at least two magnetometer units (S1 , S2), and to determine an effective magnetic field strength and an effective field direction from the magnetic field strengths and field directions detected by means of the signal processing unit (170, 200) comprising at least one field vector.

8. Device according to one of claims 6 or 7, wherein the geometric arrangement is a two-dimensional arrangement in which the at least two magnetometer units (S1 , S2) are arranged in a plane.

9. Device according to claim 6 or 7, wherein the at least two magnetometer units (S1, S2) comprise at least four magnetometer units and wherein the geometric arrangement is a three-dimensional arrangement in which at least one of the R.414357 - 18 - at least four magnetometer units are not arranged in a plane in which at least three other of the at least four magnetometer units are arranged.

10. Device according to any one of claims 6 to 9, wherein the spin-based quantum system (110) comprises a sensor crystal with color centers, in particular a diamond with nitrogen vacancy centers.

11. Device according to any one of claims 6 to 9, wherein the spin-based quantum system comprises a vapor cell containing a mixture of at least one gaseous alkali metal and at least one gaseous noble gas.

12. Device according to any one of claims 6 to 11, wherein each of the at least two magnetometer units (S1, S2) comprises: - an excitation light source (120) for shining light (124) into the spin-based quantum system (110), and / or - at least one microwave source (150) to generate a resonant field in the spin-based quantum system (110), and / or - at least one photodetector (130) for detecting resonance-dependent fluorescence light (112) from the spin-based quantum system (110), and / or - at least one device (140) for generating a substantially homogeneous bias magnetic field at the location of the spin-based quantum system (110).

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