Non-microwave electromagnetic field measurement method and device based on NV color center

Abstract

The invention discloses a non-microwave electromagnetic field measurement method and device based on an NV color center, and relates to the field of quantum precision measurement, and the device comprises a magnetic field generation structure, a laser excitation structure, a color center selection structure and a fluorescence detection structure. The magnetic field generation structure is used for applying a magnetic field with known direction and size to the diamond; the laser excitation structure generates laser, and the laser irradiates the diamond containing the NV color center; the color center selection structure performs micron-level focusing on an objective lens by using a three-axis displacement table and selects a diamond NV color center corresponding to the size and direction of a magnetic field; the fluorescence detection structure collects fluorescence radiated by the NV color center and converts the fluorescence into an electric signal for measurement. According to the invention, by applying the magnetic field with the size of 1024G along the NV axis and the included angle within 0.1 degree, the detection of the target electromagnetic field is realized by utilizing the sensitivity to the transverse component of the electromagnetic field under the strong magnetic field; the invention discloses a non-microwave electromagnetic field measurement method and device based on an NV color center, and is suitable for magnetic field and electric field measurement of an all-optical device without a microwave assembly.

Description

Technical Field

[0001] The present invention belongs to the field of quantum precision measurement, and specifically relates to a microwave-free electromagnetic field measurement method and device based on NV color centers. Background Art

[0002] Electromagnetic field detection technology has played an important role in aerospace, biomedicine, geological exploration, integrated circuit chip detection and other fields. Diamond nitrogen vacancy color center (NV color center) has become an important tool in the field of quantum magnetic measurement due to its unique quantum spin properties. The sensors prepared using its principle have the characteristics of high spatial resolution and high sensitivity. After irradiation with 532nm laser, it can emit 637nm fluorescence, and the ground state spin is transferred from ms=±1 state to ms=0 state. The number of fluorescent photons radiated by ms=0 state is more, and the distribution can be distinguished by fluorescence intensity. Under the action of microwaves of corresponding energy, resonant transitions between energy levels will occur, which is called the principle of optical detection magnetic resonance.

[0003] The common diamond NV color center at room temperature requires the joint action of light field, magnetic field and microwave field, and can be used to measure physical quantities such as magnetic field, electric field, temperature and stress. However, microwave magnetic field is not suitable for use in some special scenarios or for some samples to be measured, and microwave magnetic field will introduce microwave power noise and microwave frequency noise, resulting in measurement errors and reducing measurement sensitivity. Microwave-free sensing technology is based on the change of NV color center photoluminescence under optical pumping conditions near the ground state energy level anticrossing (GSLAC), which requires an external strong magnetic field of 1024G. The solution using Helmholtz coils and electromagnets requires a large current to be passed, generating a large amount of heat and affecting the temperature field of the environment. The device has a large volume and power consumption. When switching the magnetic field, the inductance in the coil makes it impossible to generate / remove the strong magnetic field in time. Permanent magnets can achieve stable application of magnetic fields, but it is difficult to linearly change the size of the magnetic field by changing the position of the permanent magnet. Summary of the invention

[0004] To solve the above problems, the present invention discloses a microwave-free electromagnetic field measurement method and device based on NV color centers. A constant strong magnetic field is applied by adjusting the position of the permanent magnet, and an adjustable magnetic field is generated by the energized wire. The combination of the magnetic field generated by the permanent magnet and the current eliminates the need for complex Helmholtz coils and cooling. In the anti-crossing region of the ground state energy level, the bias magnetic field can change rapidly in a short period of time, and the on and off of the current is controlled to construct a magnetic field pulse, thereby solving the problem of miniaturization of the overall device and improving the electromagnetic field sensitivity of NV color center measurement.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A microwave-free electromagnetic field measurement device based on NV color centers includes: a magnetic field generating structure, a laser excitation structure, a color center selection structure and a fluorescence detection structure;

[0007] The magnetic field generating structure is used to generate a bias magnetic field, which includes a constant strong magnetic field and an adjustable small magnetic field; the direction of the constant strong magnetic field is parallel to the direction of the NV axis, and is used to provide a bias magnetic field of 1024G for the diamond ensemble sample; the adjustable small magnetic field is used to provide an adjustable small magnetic field of -10G to 10G for the diamond ensemble sample.

[0008] Optionally, the magnetic field generating structure includes a permanent magnet, an adjustable current source, a powered wire, an arbitrary signal generator, a Z-axis lifting platform, an angle displacement platform and an XYZ three-axis displacement platform;

[0009] The permanent magnet is a rare earth neodymium boron magnet, fixed on a mechanical platform consisting of a Z-axis lifting platform, an angle translation platform and an XYZ three-axis translation platform;

[0010] The Z-axis lifting platform is used to adjust the dynamic range of the magnetic field applied by the permanent magnet;

[0011] The angular displacement stage is used to align the direction of the permanent magnet magnetic field and the NV axis;

[0012] The XYZ three-dimensional translation stage is used to adjust the distance between the permanent magnet and the NV color center at the um level. The translation stage stroke is ±1.25cm, which can achieve more accurate magnetic field size setting and direction alignment.

[0013] The current-carrying wire is connected to an adjustable current source, the on and off of the current controls the switch of the adjustable magnetic field, and the magnitude and direction of the current correspond to the magnitude and direction of the magnetic field;

[0014] The arbitrary signal generator is used to provide a specified voltage sequence pulse to the laser, the photodetector and the energized wire.

[0015] The laser generating structure includes a laser, a focusing lens, an acousto-optic modulator, a dichroic mirror and a reflector, and is used to focus a 532nm green pump laser onto the diamond;

[0016] The laser is used to provide a 532nm green pump laser;

[0017] The focusing lens is used to focus the laser light emitted by the laser and input it into the acousto-optic modulator;

[0018] The acousto-optic modulator is used to control and modulate the laser intensity;

[0019] The dichroic mirror is used to reflect the output 532nm green laser and the red fluorescence collected by the objective lens;

[0020] The reflecting mirror is used to reflect the laser onto the diamond NV system sample;

[0021] The color center selection structure includes a diamond NV ensemble sample, a three-axis translation stage and a high numerical aperture objective lens, and by adjusting different positions of the objective lens, NV color centers under different concentrations and magnetic fields are selected for laser excitation and fluorescence collection;

[0022] The diamond NV ensemble sample is <100> In diamond, there are four axial NV color centers, all of which form an angle of 54.7° with the normal vector of the diamond section;

[0023] The high numerical aperture objective lens is used to focus the laser onto the NV color center and collect the red fluorescence radiated by the color center and return it to the fluorescence light path;

[0024] The three-axis translation stage is used to adjust the position of the objective lens and select color centers with different magnetic fields and different concentrations;

[0025] The fluorescence detection structure includes a defocusing lens, a high-pass filter and a photodetector, which are used to collect the red fluorescence radiated by the diamond NV color center. The photodetector is placed at the focus of the light path and converts the collected fluorescence into an electrical signal for processing;

[0026] The defocusing lens is used to determine the focus of the fluorescent light path;

[0027] The high-pass filter allows the fluorescence of 650nm-800nm ​​to pass through and filters out the green light passing through the dichroic mirror.

[0028] The present invention also provides a microwave-free electromagnetic field measurement method based on NV color centers, using a microwave-free electromagnetic field measurement device based on NV color centers as described above, comprising the following steps:

[0029] S1, realize the alignment along the axial direction of the NV color center under the weak magnetic field of the permanent magnet through the Z-axis lifting platform and the angle translation platform;

[0030] S2. Determine the position of the permanent magnet on the XYZ translation stage and apply a constant strong magnetic field of 1024G along the NV axis;

[0031] S3, through the adjustable small magnetic field, the fluorescence intensity is swept with respect to the magnetic field, and the size of the constant strong magnetic field and the size of the longitudinal magnetic field to be measured are determined;

[0032] S4, through the adjustable small magnetic field and the switch of the laser, the ground state spin polarization with the bias magnetic field size far away from 1024G is realized;

[0033] S5, turn off the laser and the adjustable small magnetic field, the duration is t, the ground state spin at 1024G spontaneously transitions between ms = 0 and ms = -1 in the form of Rabi oscillation, and the Rabi oscillation frequency is positively correlated with the transverse component of the electromagnetic field; Ω∝γ e B ⊥ γ e is the gyromagnetic ratio, B ⊥ is the magnitude of the transverse magnetic field to be measured, Ω is the Rabi frequency, and ∝ represents proportional to.

[0034] S6. The spin is read out by loading a laser pulse, and the fluorescence distribution degree and the magnitude of the transverse magnetic field are calculated. The magnitude of the measured transverse magnetic field is expressed as the difference in the transverse magnetic field calculated by the Rabi frequency solution when there is / is no measured magnetic field in the two measurements.

[0035] The above technical solution of the present invention has the following advantages:

[0036] The present invention has a reasonable structure and ingenious design. The position of the permanent magnet is adjusted to apply a constant strong magnetic field, and the wire generates an adjustable magnetic field. The combination of the magnetic field generated by the permanent magnet and the current eliminates the need for a complex Helmholtz coil and cooling. In the anti-crossing region of the ground state energy level, the bias magnetic field can also be changed rapidly in a short period of time, and the on-off of the current is controlled to construct a magnetic field pulse, thereby solving the problem of miniaturization of the overall device and improving the electromagnetic field sensitivity of NV color center measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of a microwave-free electromagnetic field measurement device based on NV color centers in the present invention;

[0038] List of Figure Symbols:

[0039] 1. Z-axis lifting platform, 2. Angular displacement platform, 3. XYZ three-axis displacement platform, 4. Permanent magnet, 5. Diamond NV ensemble sample, 6. Wire, 7. Objective lens, 8. Three-axis displacement platform, 9. Reflector, 10. Defocusing lens, 11. Dichroic mirror, 12. Long-pass filter, 13. Photodetector, 14. Acousto-optic modulator, 15. Focusing lens, 16. Pinhole filter, 17. Laser, 18. Adjustable current source, 19. Arbitrary waveform generator.

[0040] Figure 2 This is a schematic diagram of the microwave-free electromagnetic field measurement method based on NV color centers in the present invention. DETAILED DESCRIPTION

[0041] The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0042] Microwave-free sensing technology is based on the change of NV color center photoluminescence under optical pumping conditions near the ground state energy level anticrossing (GSLAC), which requires an external strong magnetic field of 1024G. When the hyperfine splitting of spin nuclear polarization is not considered, the ground state spin exhibits a triplet state, and the energy level splitting D = 2870MHz between ms = 0 and ms = ±1. After the magnetic field is applied, ms = ±1 undergoes degeneracy due to Zeeman splitting, and the energy level energy of spin ms = ±1 changes proportionally with the magnetic field size about 2870MHz. The energy difference between ms = 0 and ms = ±1 is Δ = D ± γB, where γ is the gyromagnetic ratio. When B = 1024G, the energy between ms = -1 and ms = 0 is the same, and this region is called the ground state energy level anticrossing region.

[0043] The microwave-free electromagnetic field measurement device and method based on NV color centers described in the present invention utilizes magnetic field sweeping of an adjustable magnetic field to achieve the measurement of the magnitude of the longitudinal component of the electromagnetic field being measured, and utilizes the spontaneous resonant transition of the anti-crossing region of the ground state energy level to construct a combined pulse of magnetic field and laser to achieve the measurement of the transverse component of the electromagnetic field being measured, thereby realizing three-dimensional vector detection of the electromagnetic field.

[0044] As shown in the figure, the microwave-free electromagnetic field measurement device based on NV color center of the present invention includes a magnetic field generating structure, a laser excitation structure, a color center selection structure and a fluorescence detection structure, specifically, wherein:

[0045] The magnetic field generating structure includes a permanent magnet 4, an adjustable current source 18, a wire 6, an arbitrary signal generator 19, a Z-axis lifting platform 1, an angle displacement platform 2 and an XYZ three-axis displacement platform 3; the permanent magnet 4 is fixed on a mechanical platform composed of the Z-axis lifting platform 1, the angle displacement platform 2 and the XYZ three-axis displacement platform 3; the Z-axis lifting platform 1 is used to adjust the dynamic range (vertical direction) of the magnetic field applied by the permanent magnet; the angle displacement platform 2 is used to adjust the angle between the permanent magnet and the diamond normal vector, and the permanent magnet is oriented at an angle of 54.7° with the diamond surface normal vector (because the position of the color center is not determined and the direction of the magnetic field is not necessarily uniform, the angle between the magnetic field and the NV is not strictly aligned, and the next step of operation is required); the XYZ three-dimensional displacement platform 3 is used for um-level adjustment of the permanent magnet position to achieve a constant strong magnetic field of 1024G within an angle of 0.1° along the NV axis; the adjustable current source 18 is connected to the wire 6, and the current is adjusted to control the size of the adjustable magnetic field; the arbitrary signal generator 19 provides a specified voltage sequence pulse to the adjustable current source 18 to control the switch of the adjustable magnetic field;

[0046] The laser excitation structure includes a laser 17, a pinhole filter 16, a focusing lens 15, an acousto-optic modulator 14, a dichroic mirror 11, a defocusing lens group 10 and a reflector 9. The laser 17 provides a 532nm green pump laser, which enters the acousto-optic modulator 14 through the pinhole filter 16 and the focusing lens 15. The acousto-optic modulator 14 acts as an optical switch to control the laser intensity and output it. After two reflections by the dichroic mirror 11, the defocusing lens 10 and the reflector 9, the laser is output as a parallel laser beam.

[0047] The color center selection structure includes a diamond NV ensemble sample 5, a three-axis translation stage 8 and a high numerical aperture objective lens 7. The objective lens 7 is fixed on the three-axis translation stage 8. The three-axis translation stage 8 is adjusted to change the position of the objective lens 7 to focus on different positions of the diamond NV ensemble sample 5.

[0048] The fluorescence detection structure includes a high-pass filter 12 and a photodetector 13. The red fluorescence collected by the objective lens 7 enters the fluorescence light path after being reflected twice by the reflector 9, the defocusing lens 10 and the dichroic mirror 11. The high-pass filter 12 allows the fluorescence of 650nm-800nm ​​to pass through and filters out the green light passing through the dichroic mirror. The photodetector 13 is placed at the focus of the silver light path and converts the collected fluorescence into electrical signals for processing.

[0049] The arbitrary signal generator 19 provides a specified sequence of pulses to the laser 17, the photodetector 13 and the adjustable current source 18 to control the polarization, manipulation and readout of the spins.

[0050] A microwave-free electromagnetic field measurement method based on NV color centers, the measurement method comprising:

[0051] (1) The permanent magnet 4 with a known magnetic field direction is fixed on a mechanical platform, the angle displacement stage 2 is adjusted to 54.7°, and the Z-axis lifting stage 1 is adjusted along the Z direction to gradually reduce the distance between the permanent magnet 4 and the diamond 5 to achieve the alignment of the permanent magnet along the NV color center axis under a weak magnetic field;

[0052] (2) Change the Z axis of the XYZ stage 3. When the fluorescence intensity suddenly extinguishes, determine the position of the permanent magnet in the Z axis direction; change the X and Y axes of the XYZ stage. When the fluorescence intensity of the stimulated radiation of diamond is the strongest, determine the position of the permanent magnet in the X and Y axis directions; use the permanent magnet to apply a constant strong magnetic field of 1024G along the NV axis;

[0053] (3) The position of the permanent magnet 4 is adjusted along the Z axis to cause sudden extinguishing of fluorescence. The direction and magnitude of the current in the energized conductor 6 are changed to realize the frequency sweep of the fluorescence intensity with respect to the magnitude of the magnetic field, and to determine the magnitude of the constant strong magnetic field. When the measured magnetic field exists, the magnitude of the longitudinal magnetic field is measured according to the magnitude of the current intensity applied when the fluorescence brightness is the darkest.

[0054] (4) Using an arbitrary waveform generator 19 to control the adjustable current source 18 and the laser 17 to turn on, fix the current output by the adjustable current source 18 to be constant and the laser output power to be stable, and in the conductive state, make the bias magnetic field size of the NV color center away from 1024G, wait for several microseconds, and polarize the ground state spin to ms=0 state under the action of the laser;

[0055] (5) Turn off the laser and the adjustable current source for a duration of t. The state spin spontaneously transitions from ms = 0 to ms = -1 in the form of Rabi oscillation at 1024G. The Rabi oscillation frequency is positively correlated with the transverse component of the electromagnetic field. Ω∝γ e B ⊥ γ e is the gyromagnetic ratio, B ⊥ is the magnitude of the transverse magnetic field to be measured, Ω is the Rabi frequency, and ∝ represents proportional to.

[0056] (6) The arbitrary waveform generator 19 controls the photodetector 13 and the laser 17 to turn on, reads the spin state by loading the laser pulse, and calculates the spin fluorescence configuration degree and the transverse magnetic field size. The size of the measured transverse magnetic field is expressed as the difference in the transverse magnetic field calculated by the Rabi frequency solution when there is / is not a measured magnetic field in the two measurements.

[0057] The size and direction of the adjustable magnetic field generated by energizing the wire along the NV axis are known, and the laser can be selectively focused on the color center subjected to different magnetic fields by adjusting the three-axis translation stage 8 .

[0058] It should be noted that the above content merely illustrates the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications all fall within the protection scope of the claims of the present invention.

Claims

1. A microwave-free electromagnetic field measurement device based on NV color centers, characterized in that: The device comprises: a magnetic field generating structure, a laser excitation structure, a color center selecting structure and a fluorescence detecting structure; The magnetic field generating structure is used to generate a bias magnetic field, and the bias magnetic field includes a constant strong magnetic field and an adjustable small magnetic field; the direction of the constant strong magnetic field is parallel to the direction of the NV axis, and is used to provide a bias magnetic field of 1024G for the diamond ensemble sample; the adjustable small magnetic field is used to provide an adjustable small magnetic field of -10G to 10G for the diamond ensemble sample; The laser generating structure is used to focus the 532nm green pump laser onto the diamond; the color center selection structure selects NV color centers of different concentrations and magnetic fields for laser excitation and fluorescence collection by adjusting different positions of the objective lens; the fluorescence detection structure is used to collect the red fluorescence radiated by the diamond NV color center, and the photodetector is placed at the focus of the optical path, and the collected fluorescence is converted into an electrical signal for processing.

2. The microwave-free electromagnetic field measurement device based on NV color centers according to claim 1, characterized in that: The magnetic field generating structure includes a permanent magnet, an adjustable current source, a energized wire, an arbitrary signal generator, a Z-axis lifting platform, an angle displacement platform and an XYZ three-axis displacement platform; the permanent magnet is a rare earth neodymium boron magnet, fixed on a mechanical platform composed of a Z-axis lifting platform, an angle displacement platform and an XYZ three-axis displacement platform; the Z-axis lifting platform is used to adjust the dynamic range of the magnetic field applied by the permanent magnet; the angle displacement platform is used to align the direction of the permanent magnet magnetic field and the NV axis; the XYZ three-dimensional displacement platform is used to adjust the um-level distance between the permanent magnet and the NV color center, and the displacement platform stroke is ±1.25cm, so as to achieve more accurate magnetic field size setting and direction alignment; the wire is connected to the adjustable current source, and the on and off of the current controls the switch of the adjustable magnetic field, and the size and direction of the current correspond to the size and direction of the magnetic field; the arbitrary signal generator is used to provide a specified voltage sequence pulse to the laser, photodetector and wire.

3. The microwave-free electromagnetic field measurement device based on NV color centers according to claim 1, characterized in that: The laser generating structure comprises a laser, a focusing lens, an acousto-optic modulator, a dichroic mirror and a reflecting mirror; The laser is used to provide a 532nm green pump laser; the focusing lens is used to focus the laser emitted by the laser and input it into the acousto-optic modulator; the acousto-optic modulator is used to control and modulate the laser intensity; the dichroic mirror is used to reflect the output 532nm green laser and the red fluorescence collected by the objective lens; the reflector is used to reflect the laser onto the diamond NV system sample.

4. The microwave-free electromagnetic field measurement device based on NV color centers according to claim 1, characterized in that: The color center selection structure comprises a diamond NV ensemble sample, a three-axis translation stage and a high numerical aperture objective lens; the diamond NV ensemble sample is <100> Diamond has four axial NV color centers, and all of them form an angle of 54.7° with the normal vector of the diamond section; the high numerical aperture objective lens is used to focus the laser on the NV color center and collect the red fluorescence radiated by the color center and return it to the fluorescence light path; the three-axis translation stage is used to adjust the position of the objective lens and select color centers with different concentrations in different magnetic fields.

5. The microwave-free electromagnetic field measurement device based on NV color centers according to claim 1, characterized in that: The fluorescence detection structure includes a defocusing lens, a high-pass filter and a photodetector; the defocusing lens is used to determine the focus of the fluorescence light path; the high-pass filter allows 650nm-800nm ​​fluorescence to pass through and filters out the green light passing through the dichroic mirror; the photodetector is placed at the focus of the fluorescence light path and converts the optical signal into an electrical signal for processing.

6. A microwave-free electromagnetic field measurement method based on NV color centers, applied to a microwave-free electromagnetic field measurement device based on NV color centers as described in claims 1-5, characterized in that: The method comprises: (1) Preliminarily determine the magnetic field direction of the permanent magnet, and adjust the Z-axis lifting platform and the angle translation stage to achieve alignment along a certain axial angle of the NV color center under weak magnetic field conditions; (2) Adjust the Z axis of the XYZ stage to increase the magnetic field strength. When the fluorescence intensity suddenly extinguishes, determine the position of the permanent magnet in the Z axis direction; adjust the X and Y directions of the XYZ stage to make the fluorescence intensity of the diamond stimulated radiation the strongest, determine the position of the permanent magnet in the X and Y axis directions and thus determine the direction of the magnetic field; use the permanent magnet to apply a constant strong magnetic field of 1024G along the NV axis; (3) Apply an adjustable small magnetic field, change the magnitude and direction of the wire current to achieve a frequency sweep of the fluorescence intensity with respect to the magnetic field. When the fluorescence is the darkest without current, adjust the constant strong magnetic field to 1024G; (4) Fix the small magnetic field size so that the bias magnetic field size of the NV color center is far away from 1024G, turn on the laser pulse, and the electrons transition from the ground state to the excited state. After waiting for a few microseconds, the ground state spin polarization reaches ms = 0; (5) Turn off the laser and adjustable magnetic field for a duration of t. The ground state spin spontaneously transitions from ms = 0 to ms = -1 in the form of Rabi oscillation at 1024 G. The oscillation frequency is positively correlated with the transverse component of the electromagnetic field. Ω∝γ e B ⊥ γ e The gyromagnetic ratio is 2.8MHz / G, B ⊥ is the magnitude of the transverse magnetic field to be measured, Ω is the Rabi frequency; ∝ represents proportional to; (6) The spin state is read out by loading laser pulses, and the fluorescence distribution degree and transverse magnetic field size are further calculated.

7. The microwave-free electromagnetic field measurement method based on NV color centers according to claim 6 is characterized in that: The position of the permanent magnet is adjusted along the Z axis to cause sudden extinguishing of fluorescence. The direction and magnitude of the conductor current are changed to achieve a frequency sweep of the fluorescence intensity with respect to the magnetic field. When the measured magnetic field exists, the magnitude of the longitudinal magnetic field component is calculated based on the current intensity applied when the fluorescence brightness is the darkest.

8. The microwave-free electromagnetic field measurement method based on NV color centers according to claim 6, characterized in that: There is a slight deviation in the alignment of the magnetic field along the NV axis, and there is a transverse component other than the measured magnetic field. The magnitude of the measured transverse magnetic field is expressed as the difference in the transverse magnetic field calculated by the Rabi frequency solution when the measured magnetic field is present and absent in the two measurements.

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