A method and device for polarizing electron and nuclear spins in a single NV color center

Abstract

The present invention relates to a method for polarizing electron and nuclear spins in a single NV color center and a device for realizing the same. The polarization method provided by the present invention can simultaneously polarize the electron and nuclear spins in a single NV color center, and the polarization rate can reach more than 95%. The polarization process does not require the use of the NV ensemble to calibrate the magnetic field angle. The magnitude and direction of the magnetic field are changed by adjusting the position of the magnet, and the angle accuracy is better than 0.6 degrees, eliminating the need for complex Helmholtz coils and cooling measures. The device provided by the present invention has a relatively simple structural design, a low device cost, and excellent stability. After being positioned at a single color center, fluorescence information can be stably collected for a long time, and the fluorescence intensity fluctuation can be guaranteed to be less than 6% within 1 hour, and the saturation count rate is 150k counts / s.

Description

Technical Field

[0001] The invention relates to a method for polarizing electron and nuclear spins in a single NV color center and a device for realizing the polarization, and belongs to the technical field of spin state control in diamond nitrogen vacancy color centers. Background Art

[0002] Diamond is composed of carbon atoms. When a nitrogen atom replaces a carbon atom and there is a vacancy defect in the adjacent position, a single NV color center is formed, such as Figure 1 As shown in the figure, a valley value lower than 0.5 is considered to be a single color center. NV color center is a luminescent point defect in diamond, in English nitrogen-vacancy center. After irradiation with a 532nm wavelength laser, it can emit fluorescence with a central wavelength of 637nm. The decoherence time of the diamond nitrogen vacancy color center system at room temperature is as long as milliseconds. The spin state can be initialized by laser, and the spin state can be read according to the intensity of the fluorescence. The electron spin in the nitrogen vacancy color center, the nitrogen 14 nuclear spin and the randomly distributed carbon 13 nuclear spin around it can be used as quantum bits, providing the possibility for the expansion of quantum systems. Because of the many advantages of this system, the nitrogen vacancy color center system can be used in many fields such as quantum sensing, quantum storage, and quantum simulation, and has broad application prospects.

[0003] In the field of quantum computing and simulation, it is necessary to polarize the electron spin and nuclear spin in a single NV color center to a certain state at the same time and prepare a specific initial state, which requires applying an external magnetic field of a certain strength along the NV axis (the straight line connecting the nitrogen atom and the vacancy). The magnetic field angle can be measured using the ensemble color center, and the existing measurement scheme is not applicable to a single NV color center; and if a coil is used to apply the magnetic field, the structure will be very complicated and require additional cooling measures.

[0004] In addition, since the fluorescence signal emitted by the color center is needed to assist in the regulation of the external magnetic field, it is necessary to design a highly stable fluorescence collection device. Currently, many fluorescence collection devices are generally suitable for an ensemble system composed of multiple color centers. The size of this system is in the micrometer range, and the performance requirements for the fluorescence collection device are relatively small. In terms of quantum storage and quantum simulation, a single color center is generally used in experiments, which brings a series of challenges. First, the size of a single color center is at the atomic scale. When the laser focus position deviates from the color center by more than ten nanometers, the fluorescence signal will be significantly reduced. Secondly, due to the limitation of the numerical aperture of the microscope objective, the collection efficiency of the collection system is not high, and only a very small part of the fluorescence signal emitted by the color center can be received. In order to reduce the impact of noise on experimental data and obtain reliable experimental data, it is necessary to accurately locate the color center position for a long time to collect fluorescence signals. The temperature changes and vibrations of the equipment during the long-term collection process will lead to unsatisfactory experimental data. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention provides a method for polarizing the electron and nuclear spins in a single NV color center and a device for implementing the method. The polarization method provided by the present invention can simultaneously polarize the electron spins and nuclear spins in a single NV color center, and the polarization rate can reach more than 95%. The polarization process does not require the use of the NV ensemble to calibrate the magnetic field angle. The magnitude and direction of the magnetic field are changed by adjusting the position of the magnet. The angle accuracy is better than 0.6 degrees, eliminating the complex structure of the Helmholtz coil and cooling measures.

[0006] The technical solution of the present invention is:

[0007] A method for polarizing electron and nuclear spins in a single NV color center, the polarization method comprising:

[0008] (1) The objective lens is roughly focused at the μm level along the Z axis, and then the microwave antenna carrying the diamond is roughly adjusted at the μm level along the X and Y axis directions, so that the laser beam is roughly focused on the diamond;

[0009] (2) Finely adjust the microwave antenna carrying diamond along the Z-axis by the order of nanometers to make the fluorescence intensity of the diamond excited strongest, thereby determining the position of the microwave antenna in the Z-axis direction;

[0010] (3) Apply a magnetic field to the diamond through a permanent magnet, and preliminarily determine the horizontal angle θ and vertical angle φ of the permanent magnet, so that the magnetic field direction of the permanent magnet at the position of the diamond color center is roughly parallel to the NV axis; taking the optical platform where the diamond is located as a reference, when the rotation axis is perpendicular to the optical platform, the rotation angle around this axis is the horizontal angle θ; when the rotation axis is parallel to the optical platform, the rotation angle around this axis is the vertical angle φ;

[0011] (4) Finely adjust the diamond microwave antenna in the X and Y directions at the nanometer level to maximize the fluorescence intensity of the diamond, thereby determining the position of the microwave antenna in the X and Y directions, and ultimately allowing the laser beam to be accurately focused on the NV color center of the diamond;

[0012] (5) Determine the position of the permanent magnet in the Z-axis direction according to the magnitude of the magnetic field to be applied; then adjust the horizontal and vertical coordinates of the permanent magnet so that the fluorescence intensity of the diamond is the strongest, and determine the position of the permanent magnet in the X-axis and Y-axis directions, so that the magnetic field direction of the permanent magnet at the color center position is parallel to the NV axis;

[0013] (6) Adjust the microwave frequency applied to the NV color center and optically detect the |m in the magnetic resonance image s =0,m I =1> The signal of the corresponding valley is enhanced, |m s =0,m I =-1> and |m s =0,m I=0> The signals of the valleys corresponding to the two energy levels are submerged in the noise. When the light detects the magnetic resonance image, |m s =0,m I =1>When the spin polarization rate of the energy level state exceeds 95%, it is considered that the polarization of the electron spin and nuclear spin states in the single NV color center is achieved.

[0014] Single NV color center corresponds to the electron spin ground state Hamiltonian γ e represents the electron gyromagnetic ratio, S represents the electron spin, B represents the external magnetic field, D represents the zero-field splitting, S z Represents the component of the electron spin in the Z direction.

[0015] The ground state of the NV color center has an electron spin magnetic quantum number m s =0, ±1 corresponding to the three energy levels, in m s =0 energy level, the fluorescence intensity is large, and at m s = ±1 energy level, the fluorescence intensity is small; in experiments, only m is generally used s =0, -1 two energy levels.

[0016] The nuclear spin magnetic quantum number m of nitrogen 14 I =0, ±1, after the nitrogen 14 nuclear spin interacts with the NV color center electron spin, we get |m s =0,m I =0>、|m s =0,m I =1>|m s =0,m I =-1>,|m s =-1, m I =0>、|m s =-1, m I =0, +1> and |m s =-1, m I =0, -1> six energy levels; when no magnetic field is applied, after laser polarization, the NV color center is in |m s =0,m I =0, ±1> There are population distributions on the three energy levels. A Gaussian magnetic field with a certain intensity range is applied to the NV axis. After laser polarization, the color center state is polarized to |m s =0,m I =1>. To perform spin polarization, it is first necessary to precisely align the NV axis and apply a large magnetic field, which is applied by a permanent magnet on a multi-dimensional translation stage.

[0017] In addition, the NV axis cannot be measured in a simple way. This application provides an adjustment method to make the NV axis coincide with the magnetic field direction, that is, to use the fluorescent signal to determine the magnetic field direction, and define the NV axis as the z direction. When the magnetic field direction is collinear with the NV axis or the magnetic field strength in the vertical z direction is small (a few Gauss), only the z-direction component of the electron spin needs to be paid attention to. The energy level state is as described above. After laser polarization, the color center is in the state with the strongest fluorescence. If the magnetic field strength in the vertical z direction is large, the ground state energy level of the color center is m s Corresponding to the mixed state of three energy levels, the fluorescence intensity becomes smaller. After scanning and locating the color center, first fix the horizontal angle θ and the vertical angle φ, and continuously adjust the position of the magnet by controlling the three-dimensional translation stage to observe the change in fluorescence intensity. Repeat this process until the position of the magnet when the fluorescence is strongest is found, and change the size of the applied external magnetic field by adjusting the distance between the magnet and the color center. An image of the fluorescence intensity changing with the position of the magnet can be obtained. The color depth represents the fluorescence intensity. When the fluorescence intensity is maximum, the angle between the magnetic field and the NV axis is minimum, and the color center state polarization is |m s =0,m I =1>.

[0018] The spin polarizability is defined as P |0，1> Indicates |m s =0,m I =1> Fluorescence intensity of energy level state, P |0，-1> Indicates |m s =0,m I =-1> Fluorescence intensity of energy level state, P |0，0> Indicates |m s =0,m I =0>The fluorescence intensity of the energy level state; The spin polarization rate can be obtained through the optical detection magnetic resonance experiment by changing the microwave frequency applied to the NV color center. When the frequency corresponds to |m s =0,m I =-1> and |m s =-1, m I =-1>,|m s =0,m I =0> and |m s =-1, m I =0>、|m s =0,m I =1> and |m s =-1, m I =1>When the energy level difference between the three pairs of energy levels is greater than 1, the fluorescence intensity becomes weaker.

[0019] When three valleys appear in the optical detection magnetic resonance image, it indicates that the spins in the color center are in the m s =0,m I =0, -1>, |ms =0,m I =0,0> and |m s =0,m I =0, 1> three states. After adding a suitable magnetic field, the optical detection magnetic resonance image |m s =0,m I =1> The signal of the corresponding valley is enhanced, and the signals of the other two valleys are submerged in the noise. When the spin polarization rate is 95%, it is considered that the states of the electron spin and nuclear spin in the color center are polarized.

[0020] Preferably, in step (5), the position of the permanent magnet in the Z-axis direction is determined according to the magnitude of the magnetic field to be applied, and the specific process is: when the permanent magnet is located at a certain position in the Z-axis direction, the microwave frequency applied to the NV color center is adjusted, and the microwave frequency corresponding to the middle valley of the optical detection magnetic resonance image is calculated to obtain the magnetic field strength, specifically: the magnetic field strength γe represents the electron gyromagnetic ratio, D represents the zero-field splitting, is the frequency of the middle valley.

[0021] Further preferably, a magnetic field of 440 to 1000 Gauss is applied in the NV axis direction, and after laser polarization, the color center state polarization is |m s =0,m I =1>. When a larger magnetic field is applied, the angle between the magnetic field and the NV axis has a greater influence on the fluorescence intensity. When the angle is close to zero, the fluorescence intensity is maximum; when the angle is larger, the NV color center spin state changes to a mixed state, and the fluorescence intensity decreases. By controlling the displacement stage to continuously adjust the position and direction of the magnet, the change in fluorescence intensity is observed. When the fluorescence intensity is maximum, the angle between the magnetic field and the NV axis is minimum, the angle accuracy can be better than 0.6 degrees, and the change in the applied magnetic field intensity is less than 10ppm.

[0022] A device for implementing a method for polarizing electron and nuclear spins in a single NV color center, used to implement the above-mentioned method for polarizing spins in a single NV color center, the device comprising a laser excitation module, a dichroic mirror, a diamond scanning and objective lens focusing module, a microwave device, a static magnetic field module and a fluorescence collection module;

[0023] The laser excitation module includes a laser, an acousto-optic modulator and a first lens group which are arranged in sequence. The acousto-optic modulator acts as an optical switch to control the output of the laser, and then the laser output by the acousto-optic modulator is shaped into a parallel laser beam with a diameter of 4 mm through the first lens group.

[0024] The diamond scanning and objective lens focusing module includes a broadband reflector, an objective lens, a Z-axis mechanical translation stage, an XY-axis mechanical translation stage and a piezoelectric platform; the XY-axis mechanical translation stage is arranged above the Z-axis mechanical translation stage, the broadband reflector and the objective lens are arranged on the Z-axis mechanical translation stage in sequence along the optical path, and the Z-axis mechanical translation stage is used to perform μm-level coarse focusing of the objective lens in the Z-axis direction; the piezoelectric platform is arranged on the XY-axis mechanical translation stage, and the piezoelectric platform is used to fix the microwave antenna carrying diamond, and perform nm-level fine adjustment of the microwave antenna carrying diamond in the three directions of X, Y and Z to accurately locate the diamond color center; the XY mechanical translation stage is used to perform μm-level adjustment of the microwave antenna carrying diamond in the X and Y directions;

[0025] Microwave equipment is used to input microwaves into the microwave antenna to manipulate the spin state of electrons;

[0026] The static magnetic field module is used to apply a magnetic field to the diamond, and by adjusting the angle between the magnetic field and the NV axis, the fluorescence intensity of the diamond output when excited is maximized;

[0027] The fluorescence collection module includes a second lens group, a third lens group, a first free space detector, a second free space detector and a 50:50BS beam splitter. After being split by the 50:50BS beam splitter, a portion of the fluorescence is shaped by the second lens group and emitted to the first free space photoelectric detector; another portion of the fluorescence is shaped by the third lens group and emitted to the fluorescence incident second free space photoelectric detector;

[0028] The laser emitted by the laser excitation module is reflected by the dichroic mirror, then reflected by the broadband reflector in the diamond scanning and objective lens focusing module to the objective lens, and then incident on the microwave antenna carrying diamond to excite the diamond. The diamond is stimulated to produce fluorescence, and the fluorescence then passes through the objective lens, broadband reflector, and dichroic mirror in sequence, and is transmitted to the fluorescence collection module for fluorescence collection.

[0029] Preferably, according to the present invention, the static magnetic field module includes a five-dimensional electric translation stage and a permanent magnet, and the five-dimensional electric translation stage includes an XYZ three-dimensional electric translation stage and two rotational translation stages.

[0030] The XYZ three-dimensional electric translation stage is used to adjust the distance between the permanent magnet and the NV color center in the X, Y, and Z directions, thereby adjusting the magnetic field strength;

[0031] The rotational translation stage includes a horizontal angle translation stage and a vertical angle translation stage; the horizontal angle translation stage is used to adjust the horizontal angle θ of the permanent magnet; the vertical angle translation stage is used to adjust the vertical angle φ of the permanent magnet;

[0032] The permanent magnet is fixed on the horizontal angle translation stage, and the permanent magnet is located above the diamond.

[0033] The XYZ three-dimensional electric translation stage is Zhuoli Hanguan’s LA50 electric translation stage, and the two angle adjustments are AKR series rotation translation stages.

[0034] Preferably according to the present invention, the permanent magnet is a rare earth neodymium iron boron magnet.

[0035] Preferably, according to the present invention, light holes are provided at the centers of the piezoelectric platform and the XY-axis mechanical translation stage, and the centers of the light holes on the piezoelectric platform, the light holes on the XY-axis mechanical translation stage, and the center of the Z-axis mechanical translation stage are located on the same vertical line.

[0036] Preferably, according to the present invention, the travel range of the piezoelectric platform in the X, Y and Z axes is 80 μm, and the position resolution is 3 nm, which is used to achieve nanometer-level fine adjustment in the X, Y and Z directions and accurately locate the NV color center.

[0037] Preferably, according to the present invention, the stroke of each axis of the XY two-axis mechanical translation stage is 10 cm, and the maximum displacement accuracy is 10 μm; the stroke of the Z-axis mechanical translation stage is 7 cm, and the maximum displacement accuracy is 10 um.

[0038] Preferably according to the present invention, the diamond scanning and objective lens focusing module is a symmetrical structure, and is made of aluminum alloy and stainless steel.

[0039] Preferably, according to the present invention, the piezoelectric platform, five-axis electric translation stage, microwave equipment, acousto-optic modulator, first free-space detector and second free-space detector in the device are controlled by self-written python platform host software in the host computer, and the switching sequence of each device is controlled by a pulse signal generator.

[0040] According to the preferred embodiment of the present invention, the outside of the device is covered with a thermal insulation material, and the thermal insulation material is a hard foam board, so as to keep the temperature inside the device stable and reduce the influence of temperature fluctuation on signal acquisition during the test.

[0041] The beneficial effects of the present invention are:

[0042] 1. The polarization method of the spin in a single NV color center provided by the present invention can simultaneously realize the polarization of the electron spin and nuclear spin in a single NV color center, and the polarization rate can reach more than 95%. The polarization process does not require the use of the NV ensemble to calibrate the magnetic field angle. The magnitude and direction of the magnetic field are changed by adjusting the position of the magnet. The magnetic field strength ranges from 440 Gauss to 1024 Gauss, and the magnetic field strength change is better than 10ppm. The magnetic field direction can be adjusted by an internal algorithm, and the angle accuracy is better than 0.6 degrees, eliminating the complex structure of the Helmholtz coil and cooling measures.

[0043] 2. The device provided by the present invention uses common metal materials, has a relatively simple structural design, a relatively simple processing process, and a relatively low device cost. This set of devices has excellent stability. After being positioned at the center of a single color, it can stably collect fluorescence information for a long time, and can ensure that the fluorescence intensity fluctuation is less than 6% within 1 hour, and the saturation count rate is 150k counts / s. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A schematic diagram showing the change of the intensity of the fluorescence signal received by the fluorescence collection module over time;

[0045] Figure 2 A schematic diagram of the structure of a device for implementing a method for polarizing electron and nuclear spins in a single NV color center provided by the present invention;

[0046] Figure 3 It is a schematic diagram of the change of fluorescence signal intensity with the XY position of the magnet;

[0047] Figure 4 is a light detection magnetic resonance image when no magnetic field is applied;

[0048] Figure 5 for light detection magnetic resonance imaging when a magnetic field is applied;

[0049] Figure 6 Schematic diagram of the fluorescence signal intensity changing with the XY position of the diamond;

[0050] Figure 7 Schematic diagram of the fluorescence signal intensity changing with the XZ position of the diamond.

[0051] 1. Piezoelectric platform, 2. XY mechanical translation stage, 3. Objective lens, 4. Z-axis mechanical translation stage, 5. Broadband reflector, 6. Laser, 7. Acousto-optic modulator, 8. First lens group, 9. Dichroic mirror, 10. Second lens group, 11. First free-space detector, 12. Second free-space detector, 13. Third lens group, 14. 50:50BS beam splitter, 15. Five-axis electric translation stage, 16. Permanent magnet, 17. Microwave equipment. DETAILED DESCRIPTION

[0052] The present invention will be further described below in conjunction with the embodiments and the accompanying drawings, but is not limited thereto.

[0053] Example 1

[0054] A method for polarizing electron and nuclear spins in a single NV color center, the polarization method comprising:

[0055] (1) The objective lens 3 is roughly focused at the μm level along the Z axis, and then the microwave antenna carrying the diamond is roughly adjusted at the μm level along the X and Y axis directions, so that the laser beam is roughly focused on the diamond;

[0056] (2) Finely adjust the microwave antenna carrying diamond along the Z-axis in the order of nanometers to make the fluorescence intensity of the diamond excited strongest, such as Figure 7 As shown, the position of the microwave antenna in the Z-axis direction is determined;

[0057] (3) Applying a magnetic field to the diamond through the permanent magnet 16, preliminarily determining the horizontal angle θ and the vertical angle φ of the permanent magnet 16, so that the magnetic field direction of the permanent magnet 16 at the position of the diamond color center is roughly parallel to the NV axis; taking the optical platform where the diamond is located as a reference, when the rotation axis is perpendicular to the optical platform, the rotation angle around this axis is the horizontal angle θ; when the rotation axis is parallel to the optical platform, the rotation angle around this axis is the vertical angle φ;

[0058] In step (3), the horizontal angle θ and vertical angle φ of the permanent magnet 16 are preliminarily determined according to the crystal plane direction of the diamond. The specific process is as follows: the diamond purchased from elementsix is ​​cut with a {100} crystal plane. There are multiple color centers in a diamond. The NV axis of the color center in the diamond has four orientations. Each NV axis orientation is about 35.3 degrees with the crystal plane, and the NV axis is parallel to one side of the diamond. First, use a Gauss meter to roughly measure the external magnetic field distribution of the magnet, and then add a magnetic field of about 300 Gauss to any axial direction. When the diamond is moved to scan and search for the color center, only the color center in this axis will emit strong fluorescence, and locate a certain color center for the next step.

[0059] (4) Figure 6 As shown, the microwave antenna of the diamond is finely adjusted in the order of nm from the X and Y axis directions to make the fluorescence intensity of the diamond excited strongest, thereby determining the position of the microwave antenna in the X and Y axis directions, and finally making the laser beam accurately focused on the NV color center of the diamond;

[0060] (5) According to the size of the magnetic field to be applied, the position of the permanent magnet 16 in the Z-axis direction is determined; then the horizontal and vertical coordinates of the permanent magnet 16 are adjusted so that the fluorescence intensity of the diamond is the strongest, and the position of the permanent magnet 16 in the X-axis and Y-axis directions is determined, so that the magnetic field direction of the permanent magnet 16 at the color center position is parallel to the NV axis;

[0061] In step (5), the position of the permanent magnet 16 in the Z-axis direction is determined according to the magnitude of the magnetic field to be applied. The specific process is: when the permanent magnet 16 is located at a certain position in the Z-axis direction, the frequency of the microwave applied to the NV color center is adjusted, such as Figure 4As shown, the intensity of the magnetic field is calculated from the microwave frequency corresponding to the middle valley in the optically detected magnetic resonance image.

[0062] Magnetic Field Strength Formula γ e represents the electron gyromagnetic ratio, B represents the external magnetic field, and D represents the zero-field splitting. is the frequency of the middle valley.

[0063] A magnetic field of 440 to 1000 Gauss is applied in the NV axis. After laser polarization, the color center state is polarized to |m s =0,m I =1>.

[0064] (6) Adjust the microwave frequency applied to the NV color center and optically detect the |m in the magnetic resonance image s =0,m I =1> The signal of the corresponding valley is enhanced, |m s =0,m I =-1> and |m s =0,m I =0> The signals of the valleys corresponding to the two energy levels are submerged in the noise. When the light detects the magnetic resonance image, |m s =0,m I =1>When the spin polarization rate of the energy level state exceeds 95%, it is considered that the polarization of the electron spin and nuclear spin states in the single NV color center is achieved.

[0065] Single NV color center corresponds to the electron spin ground state Hamiltonian γ e represents the electron gyromagnetic ratio, S represents the electron spin, B represents the external magnetic field, D represents the zero-field splitting, S z Represents the component of the electron spin in the Z direction.

[0066] The ground state of the NV color center has an electron spin magnetic quantum number m s =0, ±1 corresponding to the three energy levels, in m s =0 energy level, the fluorescence intensity is large, and at m s = ±1 energy level, the fluorescence intensity is small; in experiments, only m is generally used s =0, -1 two energy levels.

[0067] The nuclear spin magnetic quantum number m of nitrogen 14 I =0, ±1, after the nitrogen 14 nuclear spin interacts with the NV color center electron spin, we get |m s =0,m I =0>、|m s =0,m I =1>|m s =0,m I =-1>,|m s=-1, m I =0>、|m s =-1, m I =0, +1> and |m s =-1, m I =0, -1> six energy levels; when no magnetic field is applied, after laser polarization, the NV color center is at |m s =0,m I =0, ±1> There are population distributions on the three energy levels. A Gaussian magnetic field with a certain intensity range is applied to the NV axis. After laser polarization, the color center state is polarized to |m s =0,m I =1>. To perform spin polarization, it is first necessary to precisely align the NV axis and apply a large magnetic field, which is applied by a permanent magnet 16 added to the multi-dimensional translation stage.

[0068] In addition, the NV axis cannot be measured in a simple way. This application provides an adjustment method to make the NV axis coincide with the magnetic field direction, that is, to use the fluorescent signal to determine the magnetic field direction, and define the NV axis as the z direction. When the magnetic field direction is collinear with the NV axis or the magnetic field strength in the vertical z direction is small (a few Gauss), only the z-direction component of the electron spin needs to be paid attention to. The energy level state is as above. After laser polarization, the color center is in the state with the strongest fluorescence. If the magnetic field strength in the vertical z direction is large, the ground state energy level of the color center is m s Corresponding to the mixed state of three energy levels, the fluorescence intensity decreases. After scanning and locating the color center, first fix the horizontal angle θ and the vertical angle φ, and continuously adjust the position of the magnet by controlling the three-dimensional displacement stage to observe the change in fluorescence intensity. Repeat this process until the position of the magnet when the fluorescence is strongest is found, and change the size of the applied external magnetic field by adjusting the distance between the magnet and the color center. An image of the fluorescence intensity changing with the position of the magnet can be obtained, and the color depth represents the fluorescence intensity, such as Figure 3 As shown in Figure 2, when the fluorescence intensity is maximum, the angle between the magnetic field and the NV axis is minimum, and the color center state polarization is |m s =0,m I =1>.

[0069] The spin polarizability is defined as P |0，1> Indicates |m s =0, mI = 1> Fluorescence intensity of energy level state, P |0，-1> Indicates |m s =0,m I =-1> Fluorescence intensity of energy level state, P |0，0> Indicates |m s =0,m I =0>The fluorescence intensity of the energy level state; The spin polarization rate can be obtained through the optical detection magnetic resonance experiment by changing the microwave frequency applied to the NV color center. When the frequency corresponds to |m s =0,mI =-1> and |m s =-1, m I =-1>,|m s =0,m I =0> and |m s =-1, m I =0>、|m s =0,m i =1> and |m s =-1, m I =1>When the energy level difference of the three pairs of energy levels is greater than 1, the fluorescence intensity becomes weaker. Figure 4 As shown in the figure, the fluorescence intensity changes with the microwave frequency. The horizontal axis represents the microwave frequency, and the vertical axis represents the rate of change of the fluorescence based on the maximum intensity. When three valleys appear in the figure, it means that the spins in the color center are in the |m s =0,m I =0, -1>, |m s =0,m i =0,0> and |m s =0,m I =0, 1> three states, Figure 4 The three valleys in the middle correspond from left to right to |m s =0,m I =0, -1>, m s =0,m I =0,0> and |m s =0,m I =0, 1> three states, the spin polarization rate is about 36%;

[0070] After adding a suitable magnetic field, such as Figure 5 As shown, in the optical detection magnetic resonance image |m s =0,m I =1> The signal of the corresponding valley is enhanced, and the signals of the other two valleys are submerged in the noise. The spin polarization rate is 95%, which means that the states of the electron spin and nuclear spin in the color center are polarized.

[0071] Example 2

[0072] A device for realizing a method for polarizing electron and nuclear spins in a single NV color center, such as Figure 2 As shown, the method for realizing the polarization of the spin in a single NV color center provided in Example 1 includes a laser excitation module, a dichroic mirror 9, a diamond scanning and objective lens 3 focusing module, a microwave device 17, a static magnetic field module and a fluorescence collection module;

[0073] The laser excitation module includes a laser 6, an acousto-optic modulator 7 and a first lens group 8 which are arranged in sequence. The acousto-optic modulator 7 is used as an optical switch to control the output of the laser, and then the laser output by the acousto-optic modulator 7 is shaped into a parallel laser beam with a diameter of 4 mm through the first lens group 8.

[0074] The diamond scanning and objective lens 3 focusing module includes a broadband reflector 5, an objective lens 3, a Z-axis mechanical displacement stage 4, an XY-axis mechanical displacement stage and a piezoelectric platform 1; the XY-axis mechanical displacement stage is arranged above the Z-axis mechanical displacement stage 4, the broadband reflector 5 and the objective lens 3 are arranged on the Z-axis mechanical displacement stage 4 in sequence along the optical path, and the Z-axis mechanical displacement stage 4 is used to perform μm-level coarse focusing of the objective lens 3 in the Z-axis direction; the piezoelectric platform 1 is arranged on the XY-axis mechanical displacement stage, and the piezoelectric platform 1 is used to fix the microwave antenna carrying diamond, and perform nm-level fine adjustment of the microwave antenna carrying diamond in the three directions of X, Y and Z to accurately locate the diamond color center; the XY mechanical displacement stage 2 is used to perform μm-level adjustment of the microwave antenna carrying diamond in the X and Y directions; wherein the wavelength range of the light reflected by the broadband reflector 5 is 400nm-1000nm.

[0075] In this embodiment, light holes are opened in the centers of the piezoelectric platform 1 and the XY-axis mechanical translation stage, and the center of the light hole on the piezoelectric platform 1, the center of the light hole on the XY-axis mechanical translation stage, and the center of the Z-axis mechanical translation stage 4 are located on the same vertical line.

[0076] The travel range of the X, Y, and Z axes of the piezoelectric platform 1 is 80 μm, and the position resolution is 3 nm. It is used to achieve nanometer-level fine adjustment in the X, Y, and Z directions and accurately locate the NV color center.

[0077] The piezoelectric platform 1 is a purchased device, model number is NanoDynamics PK3L60.

[0078] In addition, the stroke of each axis of the XY two-axis mechanical translation stage is 10 cm, and the maximum displacement accuracy is 10 μm; the stroke of the Z-axis mechanical translation stage 4 is 7 cm, and the maximum displacement accuracy is 10 um.

[0079] The diamond scanning and objective lens 3 focusing module has a symmetrical structure and is made of aluminum alloy and stainless steel.

[0080] The microwave device 17 is used to input microwaves into the microwave antenna to control the spin state of the electrons; the microwave device 17 adopts the SLFS-A microwave signal source of Zhongxing Lianhua.

[0081] The static magnetic field module is used to apply a magnetic field to the diamond and adjust the angle between the magnetic field and the NV axis to maximize the output fluorescence intensity.

[0082] In this embodiment, the static magnetic field module includes a five-dimensional electric translation stage and a permanent magnet 16. The five-dimensional electric translation stage includes an XYZ three-dimensional electric translation stage and two rotational translation stages.

[0083] The XYZ three-dimensional electric translation stage is used to adjust the distance between the permanent magnet 16 and the NV color center in the X, Y, and Z directions, thereby adjusting the magnetic field strength;

[0084] The rotational displacement stage includes a horizontal angle displacement stage and a vertical angle displacement stage; the horizontal angle displacement stage is used to adjust the horizontal angle θ of the permanent magnet 16; the vertical angle displacement stage is used to adjust the vertical angle φ of the permanent magnet 16;

[0085] The permanent magnet 16 is fixed on the horizontal angle displacement stage, and the permanent magnet 16 is located above the diamond.

[0086] The XYZ three-dimensional electric translation stage is Zhuoli Hanguan’s LA50 electric translation stage, and the two angle adjustments are AKR series rotation translation stages.

[0087] The permanent magnet 16 is a rare earth neodymium iron boron magnet.

[0088] The fluorescence collection module includes a second lens group 10, a third lens group 13, a first free space detector 11, a second free space detector 12 and a 50:50BS beam splitter. After being split by the 50:50BS beam splitter, a portion of the fluorescence is shaped by the second lens group 10 and emitted to the first free space photoelectric detector; another portion of the fluorescence is shaped by the third lens group 13 and emitted to the fluorescence incident second free space photoelectric detector.

[0089] The laser emitted by the laser excitation module is reflected by the dichroic mirror 9, and then reflected by the broadband reflector 5 in the diamond scanning and objective lens 3 focusing module to the objective lens 3, and then incident on the microwave antenna carrying diamond to excite the diamond. The diamond is stimulated to produce fluorescence, and the fluorescence then passes through the objective lens 3, the broadband reflector 5, and the dichroic mirror 9 in sequence, and is transmitted to the fluorescence collection module for fluorescence collection.

[0090] The piezoelectric platform 1, five-axis electric translation stage 15, microwave device 17, acousto-optic modulator 7, first free space detector 11 and second free space detector 12 in the device are controlled by self-written python platform host software in the host computer, and the switching sequence of each device is controlled by a pulse signal generator.

[0091] The outside of the device is covered with insulation material, and the insulation material is made of hard foam board to keep the temperature inside the device stable and reduce the impact of temperature fluctuations on signal acquisition during the test.

[0092] Figure 1This is a schematic diagram of the change in the intensity of the fluorescence signal received by the fluorescence collection module over time. The horizontal axis is the relative delay between the two free-space detectors, and the vertical axis is the second-order correlation function. The mathematical expression is: n1, n2 are the photon counts on the two detectors, <…> is the average within the observation time t, and τ is the relative delay between the two free-space detectors. The fluorescence is divided into two paths by a 50:50 BS beam splitter 14, and the two-path counts are obtained by two detectors. The delay is achieved by post-processing the detection data. When the color center is a single-color center, it is a single-photon source. When τ = 0, g (2) (0)→0. Figure 1 It can be seen that the device for implementing the method for polarizing the electron and nuclear spins in a single NV color center provided by the present invention realizes the polarization of the electron and nuclear spins in a single NV color center.

Claims

1. A method for polarizing electron and nuclear spins in a single NV color center, characterized in that: The polarization method includes: (1) The objective lens is roughly focused at the μm level along the Z axis, and then the microwave antenna carrying the diamond is roughly adjusted at the μm level along the X and Y axis directions, so that the laser beam is focused on the diamond; (2) Finely adjust the microwave antenna carrying diamond along the Z-axis by the order of nanometers to make the fluorescence intensity of the diamond excited strongest, thereby determining the position of the microwave antenna in the Z-axis direction; (3) Apply a magnetic field to the diamond through a permanent magnet to preliminarily determine the horizontal angle θ and vertical angle of the permanent magnet Make the magnetic field direction of the permanent magnet at the diamond color center position parallel to the NV axis; take the optical platform where the diamond is located as the reference, when the rotation axis is perpendicular to the optical platform, the rotation angle around this axis is the horizontal angle θ; when the rotation axis is parallel to the optical platform, the rotation angle around this axis is the vertical angle (4) Adjust the diamond's microwave antenna in the X and Y directions at the nanometer level to maximize the fluorescence intensity of the diamond, thereby determining the position of the microwave antenna in the X and Y directions, and ultimately allowing the laser beam to be accurately focused on the NV color center of the diamond; (5) According to the size of the magnetic field to be applied, the position of the permanent magnet in the Z-axis direction is determined; the specific process is: when the permanent magnet is located at a certain position in the Z-axis direction, the microwave frequency applied to the NV color center is adjusted, and the microwave frequency corresponding to the middle valley of the optical detection magnetic resonance image is calculated to obtain the magnetic field strength, which is: γ e represents the electron gyromagnetic ratio, D represents the zero-field splitting, is the frequency of the middle valley; Then adjust the horizontal and vertical coordinates of the permanent magnet so that the fluorescence intensity of the diamond is the strongest, and determine the position of the permanent magnet in the X and Y axis directions so that the magnetic field direction of the permanent magnet at the color center position is parallel to the NV axis; (6) Adjust the microwave frequency applied to the NV color center, and when the optical detection magnetic resonance image |m s =0,m I =1>When the spin polarization rate of the energy level state exceeds 95%, it is considered that the polarization of the electron spin and nuclear spin states in the single NV color center is achieved.

2. The method for polarizing electron and nuclear spins in a single NV color center according to claim 1, characterized in that: A magnetic field of 440 to 1000 Gauss is applied in the NV axis. After laser polarization, the color center state is polarized to |m s =0,m I =1>.

3. A device for implementing a method for polarizing electron and nuclear spins in a single NV color center according to any one of claims 1 to 2, characterized in that: The device includes a laser excitation module, a dichroic mirror, a diamond scanning and objective lens focusing module, a microwave device, a static magnetic field module and a fluorescence collection module; The laser excitation module includes a laser, an acousto-optic modulator and a first lens group which are arranged in sequence. The acousto-optic modulator is used as an optical switch to control the output of the laser, and then the laser output by the acousto-optic modulator is shaped into a parallel laser beam through the first lens group. The diamond scanning and objective lens focusing module includes a broadband reflector, an objective lens, a Z-axis mechanical translation stage, an XY-axis mechanical translation stage and a piezoelectric platform; the XY-axis mechanical translation stage is arranged above the Z-axis mechanical translation stage, the broadband reflector and the objective lens are arranged on the Z-axis mechanical translation stage in sequence along the optical path, and the Z-axis mechanical translation stage is used to focus the objective lens at the μm level in the Z-axis direction; The piezoelectric platform is set on the XY axis mechanical displacement platform. The piezoelectric platform is used to fix the microwave antenna carrying diamonds and adjust the microwave antenna carrying diamonds in the three directions of X, Y and Z by the order of nm to accurately locate the diamond color center. The XY mechanical translation stage is used to adjust the diamond-carrying microwave antenna in the X and Y directions at the μm level; Microwave equipment is used to input microwaves into the microwave antenna to manipulate the spin state of electrons; The static magnetic field module is used to apply a magnetic field to the diamond, and by adjusting the angle between the magnetic field and the NV axis, the fluorescence intensity of the diamond output when excited is maximized; The fluorescence collection module includes a second lens group, a third lens group, a first free space detector, a second free space detector and a 50:50BS beam splitter. After being split by the 50:50BS beam splitter, a portion of the fluorescence is shaped by the second lens group and emitted to the first free space photoelectric detector; another portion of the fluorescence is shaped by the third lens group and emitted to the fluorescence incident second free space photoelectric detector; The laser emitted by the laser excitation module is reflected by the dichroic mirror, then reflected by the broadband reflector in the diamond scanning and objective lens focusing module to the objective lens, and then incident on the microwave antenna carrying diamond to excite the diamond. The diamond is stimulated to produce fluorescence, and the fluorescence then passes through the objective lens, broadband reflector, and dichroic mirror in sequence, and is transmitted to the fluorescence collection module for fluorescence collection.

4. The device for implementing the method for polarizing electron and nuclear spins in a single NV color center according to claim 3, characterized in that: The static magnetic field module includes a five-dimensional electric translation stage and a permanent magnet. The five-dimensional electric translation stage includes an XYZ three-dimensional electric translation stage and two rotational translation stages. The XYZ three-dimensional electric translation stage is used to adjust the distance between the permanent magnet and the NV color center in the X, Y, and Z directions, thereby adjusting the magnetic field strength; The rotation platform includes a horizontal angle platform and a vertical angle platform; the horizontal angle platform is used to adjust the horizontal angle θ of the permanent magnet; the vertical angle platform is used to adjust the vertical angle θ of the permanent magnet. Make adjustments; The permanent magnet is fixed on the horizontal angle translation stage, and the permanent magnet is located above the diamond.

5. The device for implementing the method for polarizing electron and nuclear spins in a single NV color center according to claim 4, characterized in that: The permanent magnet is a rare earth neodymium iron boron magnet.

6. The device for implementing the method for polarizing electron and nuclear spins in a single NV color center according to claim 3, characterized in that: The centers of the piezoelectric platform and the XY-axis mechanical translation stage are both provided with light-through holes, and the center of the light-through hole on the piezoelectric platform, the center of the light-through hole on the XY-axis mechanical translation stage, and the center of the Z-axis mechanical translation stage are located on the same vertical line; The travel of the piezoelectric platform in the X, Y, and Z axes is 80 μm, and the position resolution is 3 nm. It is used to achieve nanometer-level adjustment in the X, Y, and Z directions and accurately locate the NV color center. The stroke of each axis of the XY two-axis mechanical translation stage is 10cm, and the maximum displacement accuracy is 10μm; the stroke of the Z-axis mechanical translation stage is 7cm, and the maximum displacement accuracy is 10um.

7. The device for implementing the method for polarizing electron and nuclear spins in a single NV color center according to claim 3, characterized in that: The diamond scanning and objective lens focusing module has a symmetrical structure and is made of aluminum alloy and stainless steel.

8. The device for implementing the method for polarizing electron and nuclear spins in a single NV color center according to claim 3, characterized in that: The piezoelectric platform, five-axis electric translation stage, microwave equipment, acousto-optic modulator, first free-space detector and second free-space detector in the device are controlled by a host computer, and the switching sequence of each device is controlled by a pulse signal generator.

9. The device for implementing the method for polarizing electron and nuclear spins in a single NV color center according to claim 3, characterized in that: The outside of the device is covered with a thermal insulation material, and the thermal insulation material is a hard foam board.

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