Devices that utilize electron Zeeman splitting

Abstract

A device utilizing the electron Zeeman splitting effect includes a solid-state material including at least one spin defect. The device further includes a magnetic field generator configured to generate a bias magnetic field and a compensation system to compensate for the effect of temperature changes on the bias magnetic field. The compensation includes a temperature sensor configured to measure either a temperature and a temperature change of the magnetic field generator, and a computer device configured to determine a change in the bias magnetic field as a result of a change in the measured temperature or the measured temperature change. The computer device is further configured to use the determined change in the bias magnetic field to adjust a predetermined bias magnetic field value and to use this value as an input to the compensation system to compensate for the effect of temperature changes on the bias magnetic field.

Description

[Technical Field]

[0001] The present invention relates to the field of devices that utilize the electronic Zeeman effect, particularly devices that include diamond material. [Background technology]

[0002] Sensor devices such as magnetometers can be formed using single crystal diamond sensors that incorporate spin defects into the crystal lattice. An example of a spin defect is the nitrogen-vacancy (NV) center. Exemplary magnetometers are described in WO 2009 / 073736 and U.S. Patent Application Publication No. 2010 / 0315079.

[0003] An important aspect of the principle of spin-based magnetic field sensors is the electronic Zeeman effect, which describes the interaction between the magnetic dipole moment of the unpaired electron in a defect and the magnetic field. In defects such as NV centers in diamond, where the electron spin (S) is 1, the ground state spin level (M S ±1) energy of the defect <111> A splitting proportional to first order occurs in the magnetic field projected along the axis of symmetry. This energy splitting can be measured by optically exciting the defect with green light while sweeping the applied RF frequency and detecting the degree of NV-associated light emission (optically detected magnetic resonance, or ODMR modality) or by measuring the generated photocurrent (optically detected magnetic resonance, or PDMR). Knowledge of this energy splitting can be used to determine the magnetic field.

[0004] Magnetometers typically use a bias magnet to apply a fixed, known magnetic field, which plays different roles depending on the exact technique used.

[0005] In the implementation (called implementation 1) that utilizes static or time-varying application of microwave-frequency waves, a bias magnetic field (B bias ) but two ΔM S±1 transitions (ΔMS±1 transitions) and the (maximum) four symmetry-related sites that the NV center can occupy (four allowed <111> The resonance lines are thus sufficiently separated in frequency that we can address (up to) eight pairs of resonance lines oriented along angles of (18,29) degrees (in spherical polar θ, φ notation) as shown in Figure 1, where 0111 is defined as (54.7,45) degrees. To observe all the resonance lines, we must change the orientation of Bbias to each symmetric angle. <111> These frequency positions must then be chosen to be at different angles to the axis. Then, by measuring these frequency positions, their absolute positions or separation distances can be used to calculate the total vector magnetic field (B total ) can be extracted. In the latter case, the problem of temperature change in the diamond causing misalignment of the lines due to the change in the zero field parameters of the NV centers is denied. Then, B unknown =B total -B bias The magnetic field of interest can be extracted via Bbias, which is known by magnetic design or can be determined by measuring the magnetic field with the sensor itself in a shielded enclosure. bias Typical values ​​of are ~1-10 mT.

[0006] Another approach (called Implementation 2) for magnetic field sensors using NV centers in diamond eliminates the need for microwave application ("RF-free" technique), which is advantageous for some applications, especially those interested in performing measurements at extremely low temperatures, since applying RF generates heat. In this case, B is used to take advantage of the level anti-crossing of the triplet ground state, which reduces the luminescence output of the NV centers. bias An accurate bias field of (B unknown A change in the magnetic field (presumably due to a change in the magnetic field) enhances the luminescence.

[0007] The electron Zeeman interaction and the application of known static magnetic fields are also important for other spin defect detection modalities / use cases in solid materials. For example, as described in WO 2016 / 066532, NV in diamond has also been demonstrated as an RF spectrum analyzer where a magnetic field gradient is set across the diamond plate. By measuring the light emission as a function of position across the diamond sample (corresponding to varying B), the spectrum of RF frequencies incident on the diamond sample can be resolved.

[0008] Diamond has also been demonstrated as a MASER utilizing NV centers and Zeeman interactions (as described in US Patent Application Publication No. 20170077665 A1), where a controlled magnetic field in combination with a resonator is used to tune the frequency of the generated microwave radiation. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2009 / 073736 [Patent Document 2] US Patent Application Publication No. 2010 / 0315079 [Patent Document 3] International Publication No. 2016 / 066532 [Patent Document 4] US Patent Application Publication No. 2017 / 0077665 [Non-patent literature]

[0010] [Non-Patent Document 1] Kim and Doose, "Temperature compensation of NdFeB permanent magnets," Proceedings of the 1997 Particle Accelerator conference Summary of the Invention [Problem to be solved by the invention]

[0011] When used in magnetic measurements, NV centers have been described as a "calibration-free" means of measuring magnetic fields. However, from the above description, it is clear that NV centers measure B total and B unkown is B total From B bias In both cases, B bias It can be understood that must be known and stable.

[0012] With this setting, B bias To provide a stable B, one or more permanent magnets, often made of neodymium (NeFeB), are typically used. The use of permanent magnets is considered preferable to the use of electromagnetic coils due to their size and simplicity of setup, as well as short-term stability. bias A stable current source is required to generate

[0013] It has been understood that the temperature change of diamond must be taken into consideration. However, the temperature change and its B bias The issue of the effect of ambient temperature on the magnet's magnetic field is an area that has not been considered until now. When the ambient temperature changes, a permanent magnet will exhibit a corresponding reversible change in its magnetic field.

[0014] Considering implementation 1, NeFeB magnets exhibit a magnetic field change of ~0.12% / °C below the demagnetization temperature (e.g., -130°C to 80°C). biasIf the value of is 1mT, a temperature change of 0.1°C will bias will change by 120 nT. total For NV-based diamond sensors measuring B unknown is erroneously measured. Periodically repeating the "zeroing" procedure by placing the sensor in a shielded box is neither desirable nor practical for many applications.

[0015] In some RF-free applications described in Implementation 2, the temperature stability can be better than in Implementation 1 due to the setup. For example, RF-free applications can be used in cryostats for controlled low-temperature measurements. However, in situations where temperature control is not performed, the required magnetic fields are higher, and therefore the B bias The impact on the instability of B can be even more severe, where a 0.1°C shift bias changes by >0.012 mT.

[0016] Therefore, to produce a long-term stable, drift-free magnetic field sensor using NV centers in diamond, a stable bias field is also required, or the B bias It is clear that the effects of the above must be compensated / measured independently. The aim is to provide a solution to this problem.

[0017] A stable applied magnetic field is also important for the other sensing modalities / applications mentioned above: for example, in the case of RF spectrum analyzers, the stability of the applied magnetic field gradient affects the accuracy of the microwave frequency measurement, and in the case of MASERs, the static magnetic field affects the efficiency and stability of the emitted microwaves. [Means for solving the problem]

[0018] According to a first aspect, a device utilizing the electron Zeeman splitting effect is provided. The device includes a solid-state material containing at least one spin defect. The device further includes a magnetic field generator configured to generate a bias magnetic field and a compensation system that compensates for the effect of temperature changes on the bias magnetic field. This ensures that the device still provides accurate readings even when temperature changes affect the bias magnetic field. The compensation system includes a temperature sensor configured to measure either the temperature or temperature change of the magnetic field generator. The compensation system further includes a computer device configured to determine a change in the bias magnetic field as a result of a change in the measured temperature or the measured temperature change, and the computer device is further configured to use the determined change in the bias magnetic field to adjust a predetermined bias magnetic field value and use this value as an input to the compensation system to compensate for the effect of temperature changes on the bias magnetic field. This compensation does not directly modify any parameters of the bias magnetic field generator, but simply accounts for the change in the bias magnetic field using a calculated value.

[0019] Examples of solid materials include diamond materials and silicon carbide.

[0020] In instances where the solid material is a diamond material, the diamond material may be selected from either nanocrystalline, bulk diamond samples, or composite diamond samples comprising diamond regions with different properties.

[0021] Optionally, the spin defect is selected from any of negatively charged nitrogen vacancy centers, silicon vacancy centers, nickel-related defects, chromium-related defects, tin vacancy centers, and germanium vacancy centers.

[0022] In an optional embodiment, the solid state material is a temperature sensor, the solid state material is in thermal equilibrium with the magnetic field generator, and temperature changes are determined by the drift of the zero-field splitting values ​​of the spin defects.

[0023] In any embodiment, the device includes an intermediate material disposed between and in contact with both the solid material and the magnetic field generator, the intermediate material being selected to conduct heat between the solid material and the magnetic field generator.

[0024] Optionally, the device is a magnetometer, in which case the solid-state material includes a sensing surface proximate to the at least one spin defect, and the magnetometer further includes a detector configured to detect output optical radiation or a photocurrent correlated to the electron spin of the spin defect. The device may further include either a light source configured to generate optical radiation or an RF source configured to generate RF radiation.

[0025] Optionally, the device is selected from any of a magnetometer, a maser, and an RF sensor.

[0026] According to a second aspect, there is provided a method of using a device that utilizes the electron Zeeman splitting effect. The method includes providing a device including a solid-state material containing at least one spin defect. A bias magnetic field is generated using a magnetic field generator. A compensation system is used that is configured to compensate for the effect of temperature changes on the bias magnetic field. The compensation includes a temperature sensor that measures either the temperature or the temperature change of the magnetic field generator, and the compensation system further includes a computer device configured to determine a change in the bias magnetic field as a result of a change in the measured temperature or the measured temperature change. The computer device is further configured to use the determined change in the bias magnetic field to adjust a predetermined bias magnetic field value and use this value as an input to the compensation system to compensate for the effect of temperature changes on the bias magnetic field.

[0027] Optionally, the solid material is selected from one of a diamond material and silicon carbide.

[0028] The temperature is measured using the solid material itself, which is in thermal equilibrium with the magnetic field generator, and the temperature change is determined by the drift of the zero-field splitting value of the spin defect.

[0029] Optionally, an intermediate material is disposed between and in thermal contact with the solid material and the magnetic field generator, the intermediate material being selected to conduct heat between the solid material and the magnetic field generator.

[0030] Non-limiting embodiments will now be described by way of example with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 10 is a diagram showing the position of the resonance line with respect to the bias magnetic field. [Figure 2] FIG. 1 is a schematic block diagram of an exemplary sensor device using a magnetic flux shunt. [Figure 3] FIG. 1 is a schematic block diagram of an exemplary sensor device using a temperature sensor. [Figure 4] FIG. 1 is a schematic block diagram of an exemplary sensor device using diamond as a temperature sensor. [Figure 5] FIG. 1 is a flow diagram showing exemplary steps for calibrating a sensor device that uses diamond as a temperature sensor. [Figure 6] FIG. 1 is a flow diagram illustrating exemplary steps for using a sensor device. [Figure 7] FIG. 1 shows exemplary clear and resolvable resonance lines from ODMR. DETAILED DESCRIPTION OF THE INVENTION

[0032] The inventors of the present invention unknown B due to temperature changes when acquiring bias To ensure that variations in the magnetic field are taken into account, a compensation system was provided to compensate for the effect of temperature changes on the magnetic field.

[0033] In the following description, three exemplary types of compensation systems are presented, and a sensor device can utilize one, any two, or all three of these exemplary compensation systems. Also, although a device that uses diamond for electronic Zeeman splitting is described below, this is by way of example only, and one skilled in the art will understand that devices that utilize the electronic Zeeman splitting effect can also use other types of materials, such as silicon carbide.

[0034] Although outside the scope of this invention, the first type of compensation system requires the implementation of a compensation scheme that uses flux shunts. bias The variations in the magnetic field are compensated for by another magnetic field.

[0035] The second type of compensation system involves periodically taking precise measurements of the temperature (or temperature change) of the permanent bias magnet, mapping the temperature change from its nominal value to an expected magnetic field change, and adjusting the B bias It is necessary to change the value of

[0036] A third type of compensation system is a variation of the second type of compensation system, in which the diamond itself is configured to be in thermal equilibrium with the permanent bias magnet(s), and the temperature of the diamond, and therefore the temperature of the bias magnet, is measured using spin defects in the diamond itself. Thermal equilibrium can be achieved, for example, by placing the diamond sensor in thermal contact with the permanent bias magnet(s).

[0037] In the following description, reference will be made to NV-spin defects in diamond, but it will be understood that other spin defects such as SiV centres or any other defect that exhibits suitable properties of spin polarization and spin readout may also be used.

[0038] In a first type of compensation system, which is illustrative only and beyond the scope of the present invention, the bias magnet(s) are "shunted" by the addition of a magnetically soft material with a temperature coefficient opposite to that of the main magnetic material. The basic concept is described in Kim and Doose, "Temperature compensation of NdFeB permanent magnets," Proceedings of the 1997 Particle Accelerator conference. In this example, a flux shunt is provided for applications such as the formation of charged-beam storage rings, as well as accelerometers, torque meters, and gyroscopes. Such systems can also be used for magnetic measurements using NV centers in the diamond crystal lattice.

[0039] As stated in Kim and Doose, "At low temperatures, the shunt permeability increases, allowing the shunt to carry or shunt more magnetic flux out of the magnet's air gap. At high temperatures, the opposite condition exists: the shunt's permeability decreases, diverting less air-gap flux. To enhance temperature sensitivity, the shunt material should have a Curie point close to ambient temperature. Shunt materials made from Curie alloys (30-32% Ni-Fe) and Montell alloys (67% Ni-Cu-Fe) have relatively low Curie temperatures below 100°C."

[0040] In diamond magnetometry applications, the B bias To compensate for variations in the bias voltage, the or each bias magnet may be fitted with a compensation strip.

[0041] Using such an approach, it has been demonstrated that a temperature coefficient of 0.002% / °C can be achieved for NeFeB-based permanent magnets, which is highly advantageous for NV-based B magnetic field sensors. bias = 1 mT) for a temperature change of 0.1°C, B biasThis corresponds to a temperature-induced B total The device can operate for extended periods without requiring recalibration operations to eliminate drift in the calibration.

[0042] 2 is a schematic block diagram of an exemplary sensor device 1 using a magnetic flux shunt in accordance with the first type of compensation system. Note that this sensor device is merely exemplary and is outside the scope of the present invention. A diamond sensor 2 is provided that includes at least one spin defect disposed proximate to a sensing surface. A magnetic field generator in the form of a bias magnet 3 is disposed proximate to the diamond sensor 2. A shunt material 4 is also disposed proximate to or co-located with the bias magnet. A detector 5 is provided that detects optical emission or photocurrent from the one or more spin defects.

[0043] Turning now to the second type of compensation system, this system periodically makes accurate measurements of the temperature (or temperature change) of the permanent bias magnet, maps the temperature change from nominal to an expected change in the magnetic field, and adjusts B accordingly. bias It should be noted that this system can be used separately or simultaneously with the first type of compensation system.

[0044] 3 herein, a sensor device 6 includes a diamond sensor 2 containing at least one spin defect positioned proximate to a sensing surface. A bias magnet 7 having a well-characterized temperature coefficient is provided. A temperature sensor 8 is also provided to accurately measure the temperature of the magnet 7.

[0045] The computing device 9 includes a data input device 10 that receives temperature data from the temperature sensor 8. The processor 11 calculates B in response to changes in temperature measured by the temperature sensor. bias Calculate the change in temperature and B (or access lookup table 12). bias The calculation is performed by using the relationship between the change in

[0046] In this way, the B of the system is adjusted to compensate for temperature-induced shifts. bias value (hence, B total value) can be adjusted periodically.

[0047] Inexpensive, low-noise temperature sensors are available that can be attached to a magnet. bias The absolute accuracy of the exact temperature is not important, since all that is needed is to measure the temperature change to map it to a change in B. Assuming a measurement repeatability of 0.01°C, combined with the high temperature stability of 0.002% / °C in the optimized NeFeB configuration, a change in bias field of 0.2 nT should be detectable and can be compensated for. In this way, periodic temperature measurements can be used to measure the B measured by the NV-based sensor. total The long-term drift of the

[0048] Referring now to FIG. 4, in a third type of compensation system, the measurement of the temperature of the magnet 7 is performed by measuring the temperature of the diamond 2 using the NV defect itself. Typically, the diamond 2 is independent of the bias magnet(s) 7 and can be locally heated by the laser / LED (and potentially applied RF) used to excite the NV emission. Therefore, in the second type of compensation system, we proposed measuring the temperature of the magnet 7 directly. However, in the third type of compensation system, it is conceivable that the sensor device 13 can be configured such that the diamond 2 and the magnet 7 are in thermal equilibrium with each other, for example, by having good thermal contact between them. Optionally, thermal contact is maximized by using an intermediate material 14 that conducts heat but does not affect the B-field flux. In this way, the drift of the zero-field splitting value of the NV center can be monitored, and the measured temperature can be used to measure the B-field if the temperature coefficient of the permanent magnet(s) is well characterized. bias can be corrected.

[0049] As an example, to calibrate such a system, FIG. 5 shows exemplary steps in the following configuration. S1. Prepare an assembly of diamond 2 and bias magnet 7 with good thermal contact 14 between them, as shown in Figure 3. S2. Place the assembly in a magnetically shielded box. S3. Take measurements of B recorded by the sensor while controllably varying the temperature. In this way, it is possible to determine the change in the bias field due to temperature changes alone. Since diamond 2 resides in a magnetically shielded box, the measured change in B is due to B bias This calibration procedure is only required when the diamond and bias field magnet are in thermal equilibrium. S4. Temperature change (measured by NV centers in diamond) vs. B bias The calibration map may be stored in a look-up table 12 or a database, which the processor 11 accesses during operation to calibrate B as the temperature changes. total can be corrected.

[0050] When using the sensor device, the following exemplary steps may be performed as shown in FIG. S5. Provide a device including a solid-state material containing at least one spin defect. S6. Generate a bias magnetic field using a magnetic field generator. S7. Prepare a compensation system configured to compensate for the effect of temperature changes on the bias field. As described above, this compensation system compensates the value of the bias field based on temperature measurements and can be used in combination with a flux shunt.

[0051] As an example, the magnetic field generator can consist of a non-temperature-stabilized NeFeB magnet, which is made of four NV-containing diamonds. <111> The sensor is configured to have a magnetic field along a direction that is differently oriented relative to each of the NV axes, and the magnetic field is strong enough to resolve all eight resonance lines (required for vector sensing modalities). In this example, a sensor is constructed with a magnetic field strength of approximately 6 mT along an angle of (18,29)°, specified in the spherical-polar angular sense (where ≡0111 is defined as (54.7,45)°). Figure 7 shows the resulting ODMR and how the distinct resonance lines are clearly resolved. Figure 1 shows how the resonance line splitting varies at this fixed angle as a function of bias field strength. This figure shows that due to the finite width of the resonance lines and the additional N hyperfine splitting (inversely related to the coherence time), the applied bias field must actually be >2 mT for the resonance lines to be clearly resolved. If the bias field varies with temperature, this variation can be compensated for by calculation based on the measurement temperature, or the change in measurement temperature can compensate for the change in bias field. The compensated bias field is then used in further calculations.

[0052] Although the present invention as defined in the appended claims has been shown and described with reference to exemplary embodiments, workers skilled in the art will recognize, however, that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims.

[0053] Furthermore, although the above discussion has focused on magnetometers, other applications, such as masers, can also benefit from a compensation system that compensates for the effects of temperature changes on the bias field.

[0054] Diamond-based room-temperature masers have been shown to generate M ions from NV defects when a sufficient magnetic field (>102.5 mT) is applied. S =-1 state is MS When irradiated with light of wavelength (e.g., 532 nm), the NV-defects are converted to M S = 0, at which point a population inversion occurs. When a solid material such as NV-containing diamond is contained in a cavity (optimized for the magnetic field and microwave wavelength), a coherent microwave source can be generated by stimulated emission.

[0055] As mentioned above, temperature fluctuations cause fluctuations in the applied magnetic field, which in turn leads to M S =-1 state and M S = 0 state, thereby changing the energy gap between them and the Θ = 0 state, and therefore changing the emission wavelength. In some situations, the temperature of the environment in which the maser is placed may change (e.g., space-based applications). This may change the strength of the applied magnetic field, thereby changing the emission wavelength. Therefore, in such situations, it is useful to know the effect of temperature changes on the emission wavelength, or to use a compensation system to compensate for these variations. [Explanation of symbols]

[0056] 2 Diamond sensor 5. Detector 6 Sensor Devices 7 Bias Magnet 8 Temperature Sensor 9. Computer Equipment 10 Data input device 11 processors 12 Lookup Tables

Claims

1. A device utilizing the electron Zeeman splitting effect, the device is selected from any one of a magnetometer, a maser, and an RF sensor or a spectrum analyzer; a solid-state material containing at least one spin defect; a magnetic field generator configured to generate a bias magnetic field; a compensation system for compensating for the effects of temperature changes on the bias magnetic field; the compensation system includes a temperature sensor configured to measure one of a temperature and a temperature change of the magnetic field generator, and a computer device configured to determine a change in the bias magnetic field as a result of a change in the measured temperature or the measured temperature change, the computer device being further configured to adjust a predetermined bias magnetic field value using the determined change in bias magnetic field, and to use the adjusted predetermined bias magnetic field value as an input to the compensation system to compensate for an effect of temperature change on the bias magnetic field. A device characterized by:

2. The solid material is selected from the group consisting of a diamond material and silicon carbide. The device of claim 1 .

3. the solid material is a diamond material, the diamond material being selected from either a nanocrystalline, a bulk diamond sample, or a composite diamond sample comprising diamond regions with different properties; The device of claim 1 .

4. the spin defect is selected from the group consisting of a negatively charged nitrogen vacancy center, a silicon vacancy center, a nickel-related defect, a chromium-related defect, a tin vacancy center, and a germanium vacancy center; The device of claim 3.

5. the solid-state material is a temperature sensor, the solid-state material is in thermal equilibrium with the magnetic field generator, and the temperature change is determined by a drift in a zero-field splitting value of the spin defect. The device of claim 1 .

6. further comprising an intermediate material disposed between the solid material and the magnetic field generator and in contact with both the solid material and the magnetic field generator, the intermediate material being selected to conduct heat between the solid material and the magnetic field generator. The device of claim 1 .

7. the device is a magnetometer; the solid-state material includes a sensing surface proximate to the at least one spin defect; the magnetometer further comprising a detector configured to detect output optical radiation or photocurrent correlated to the electron spin of the spin defect. The device of claim 1 .

8. further comprising a light source configured to generate light radiation; The device of claim 7.

9. further comprising an RF source configured to generate RF radiation; 9. A device according to claim 7 or 8.

10. A method of using a device utilizing the electron Zeeman splitting effect, comprising: the device is selected from any one of a magnetometer, a maser, and an RF sensor or a spectrum analyzer; providing a device comprising a solid state material containing at least one spin defect; generating a bias magnetic field using a magnetic field generator; using a compensation system configured to compensate for the effects of temperature changes on the bias magnetic field; wherein the compensation includes a temperature sensor that measures one of a temperature and a temperature change of the magnetic field generator, and the compensation system further includes a computer device configured to determine a change in the bias magnetic field as a result of a change in the measured temperature or the measured temperature change, and the computer device is further configured to adjust a predetermined bias magnetic field value using the determined change in bias magnetic field, and to use the adjusted predetermined bias magnetic field value as an input to the compensation system to compensate for the effect of temperature change on the bias magnetic field. A method characterized by:

11. The solid material is selected from the group consisting of a diamond material and silicon carbide. The method of claim 10.

12. measuring the temperature using the solid-state material, the solid-state material being in thermal equilibrium with the magnetic field generator, and the temperature change being determined by a drift in a zero-field splitting value of the spin defect.

12. The method according to claim 10 or 11.

13. providing an intermediate material disposed between the solid-state material and the magnetic field generator in thermal contact with the solid-state material and the magnetic field generator, the intermediate material selected to conduct heat between the solid-state material and the magnetic field generator. The method of claim 12.

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