Vector electric field imaging device with nanoscale resolution

Abstract

The invention provides a nanoscale resolution vector electric field imaging device, and relates to the field of quantum imaging. The vector electric field imaging device comprises a quartz tuning fork which is movably arranged relative to the upper surface of a to-be-tested sample and is configured to perform simple harmonic vibration along a first direction; the probe is fixedly arranged on the lower surface of the quartz tuning fork and is configured to perform simple harmonic vibration along the first direction along with the quartz tuning fork, and an NV color center is carried in the probe; the microwave radiation module is configured to emit microwave pulses to the probe when the probe is located at the highest point or the lowest point of simple harmonic vibration, so that the NV color center accumulates phase information; the fluorescence acquisition module is configured to send laser to the probe and acquire fluorescence excited by the NV color center to obtain a fluorescence signal; and a processing module configured to perform vector electric field imaging based on the fluorescence signal.

Description

Technical Field

[0001] This disclosure relates to the field of quantum imaging, and more specifically, to a nanometer-resolution vector electric field imaging device. Background Technology

[0002] In recent years, scanning diamond nitrogen-vacancy center microscopy (SNVM) has flourished as a quantum imaging technique. Electron spin and nuclear spin measurement imaging have fully demonstrated the resolution and sensitivity of SNVM as an imaging method. Numerous studies have showcased the interdisciplinary capabilities of SNVM in cutting-edge science, demonstrating its potential in addressing a wide range of scientific questions, including spintronics, antiferromagnetic systems, two-dimensional magnetism, superconductor magnetic vortices, and graphene electrohydrodynamics.

[0003] Embedded in the scanning tip of the SNVM is a tiny diamond particle containing one or more NV centers (Nitrogen-Vacancy Centers). NV centers are extremely sensitive to their surrounding physical environment; physical quantities such as magnetic fields, electric fields, and temperature directly affect their quantum energy levels. NV centers possess the characteristic of readable quantum states: when illuminated with a green laser, they emit red fluorescence. By applying a specific frequency of microwave or laser pulse sequences, their quantum states can be precisely manipulated, and changes in physical signals are converted into changes in fluorescence intensity. By scanning the sample surface point by point with the tip containing the NV center and recording the corresponding fluorescence signal at each point, the physical field strength at each point on the sample surface can be measured, thus achieving quantum imaging. However, the electric field induced by the NV center through the Stark effect is 2-3 orders of magnitude weaker than the magnetic field induced through the Zeeman effect. Therefore, the weak electrical signal is easily drowned out by strong background magnetic signals, instrument noise, or noise from defects within the NV center itself, resulting in an extremely low signal-to-noise ratio. Summary of the Invention

[0004] In view of this, the present disclosure provides a nanometer-resolution vector electric field imaging device.

[0005] One aspect of this disclosure provides a nanometer-resolution vector electric field imaging device, comprising: a quartz tuning fork movably disposed relative to the upper surface of a sample to be tested, configured to perform simple harmonic oscillations along a first direction, wherein the first direction is perpendicular to the upper surface of the sample to be tested; a probe fixedly disposed on the lower surface of the quartz tuning fork, configured to perform simple harmonic oscillations along the first direction along with the quartz tuning fork, wherein the probe carries an NV color center; a microwave radiation module configured to emit microwave pulses to the probe when the probe is at the highest or lowest point of the simple harmonic oscillation, so as to accumulate phase information of the NV color center; a fluorescence acquisition module configured to send laser light to the probe and acquire the fluorescence excited by the NV color center to obtain a fluorescence signal, wherein the fluorescence signal carries the phase information accumulated by the NV color center; and a processing module configured to perform vector electric field imaging based on the fluorescence signal.

[0006] According to an embodiment of this disclosure, a differential electrode is provided on a quartz tuning fork, and the quartz tuning fork is configured to provide the piezoelectric charge generated during the simple harmonic motion to the differential electrode, wherein the polarity change period of the piezoelectric charge is consistent with the vibration period of the simple harmonic motion.

[0007] According to embodiments of this disclosure, the nanoscale resolution vector electric field imaging device further includes a control module. The control module is electrically connected to the differential electrode and configured to acquire piezoelectric charges to obtain a sinusoidal oscillating voltage signal. Based on the sinusoidal oscillating voltage signal and target time delay information, it provides a first pulse control signal to the microwave radiation module and a second pulse control signal to the fluorescence acquisition module. The microwave radiation module is configured to emit microwave pulses to the probe under the control of the first pulse control signal to modulate the electron spin state of the NV color center, thereby accumulating phase information at the NV color center. The fluorescence acquisition module, under the control of the second pulse control signal, sends a laser beam to the probe and acquires the fluorescence excited by the NV color center to obtain a fluorescence signal.

[0008] According to embodiments of this disclosure, the control module of the nanoscale resolution vector electric field imaging device includes: a charge amplifier configured to amplify the piezoelectric charge accumulated in a quartz tuning fork into a sinusoidal oscillating voltage signal; a comparator configured to convert the sinusoidal oscillating voltage signal into a square wave signal; a sequence generator configured to generate a first control signal and a second control signal based on the square wave signal and a control timing sequence; and a delay alignment unit configured to process the first control signal and the second control signal based on target delay information to obtain a first pulse control signal and a second pulse control signal, and to provide the first pulse control signal to the microwave radiation module and the second pulse control signal to the fluorescence acquisition module.

[0009] According to embodiments of this disclosure, the nanoscale resolution vector electric field imaging device further includes a displacement stage configured to adjust the positions of the quartz tuning fork and the sample to be tested, so as to adjust the probe to a preset distance from the first surface of the sample to be tested; wherein the preset distance is configured such that the NV color center of the probe is in the electric field of the first surface of the sample to be tested during simple harmonic oscillation.

[0010] According to embodiments of this disclosure, before performing vector electric field imaging of the sample to be tested, the nanoscale resolution vector electric field imaging device has a displacement stage configured to adjust the position of the quartz tuning fork so that the NV color center is at the half-width at half-maximum (WHM) position of the point spread function, which is determined by confocal scanning of the NV color center along a first direction; the processing module is configured to acquire multiple photon counts during the simple harmonic oscillation of the NV color center through the fluorescence acquisition module, and obtain the target amplitude of the NV color center based on the point spread function and the multiple photon counts.

[0011] According to embodiments of this disclosure, the nanoscale resolution vector electric field imaging device further includes an electric field generation module, which includes a first electrode, a second electrode, and a power supply. The first electrode is configured to be attached to the second surface of a quartz tuning fork, and the second electrode is configured to be positioned relative to the first electrode and used to place the sample to be tested. The first electrode and the second electrode are respectively connected to the positive and negative terminals of the power supply to generate a uniform electric field on the first surface of the sample to be tested, and the direction of the uniform electric field is consistent with the first direction.

[0012] According to embodiments of the present disclosure, the nanoscale resolution vector electric field imaging device further includes a magnetic field module, the magnetic field module including at least one magnet configured to surround the probe along a second direction, the magnetic field module being configured to provide a polarization magnetic field to the probe to modulate the NV color center into an electrical measurement state using the deflection magnetic field.

[0013] According to embodiments of this disclosure, the processing module of the nanoscale resolution vector electric field imaging device is configured to determine a first population associated with a first coherent state and a second population associated with a second coherent state based on the fluorescence signal and the target amplitude of the NV color center; determine the electric field gradient value of the current scanning point based on the first population and the second population; and obtain the vector electric field imaging result based on the electric field gradient values ​​of each of the multiple scanning points.

[0014] According to embodiments of this disclosure, the NV color center can be manipulated to mechanically vibrate in an electrostatic field. The electrostatic field is equivalent to an alternating electric field in the NV color center coordinate system. When the frequency of the alternating electric field is higher than the shielding frequency, the equivalent alternating electric field can be measured, thereby overcoming the problem of the low intensity of the electric field signal sensed by the NV color center, improving the resolution of vector electric field imaging, and improving the accuracy of vector electric field imaging by measuring the electric field through mechanical oscillator and quantum-controlled nanosecond-level synchronization. Attached Figure Description

[0015] The above and other objects, features and advantages of this disclosure will become clearer from the following description of embodiments of this disclosure with reference to the accompanying drawings, in which:

[0016] Figure 1 A schematic diagram of a nanometer-resolution vector electric field imaging apparatus according to an embodiment of the present disclosure is shown.

[0017] Figure 2 A schematic diagram of the control module of a nanometer-resolution vector electric field imaging apparatus according to an embodiment of the present disclosure is shown.

[0018] Figure 3 The illustration schematically shows a synchronous measurement sequence of a nanometer-resolution vector electric field imaging apparatus according to an embodiment of the present disclosure.

[0019] Figure 4 A schematic diagram of a nanometer-resolution vector electric field imaging apparatus according to another embodiment of the present disclosure is shown.

[0020] Figure 5 A schematic diagram of a nanometer-resolution vector electric field imaging apparatus according to another embodiment of the present disclosure is shown. Detailed Implementation

[0021] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0022] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0023] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0024] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0025] Figure 1 A schematic diagram of a nanometer-resolution vector electric field imaging apparatus according to an embodiment of the present disclosure is shown.

[0026] like Figure 1 As shown, the nanoscale resolution vector electric field imaging device according to this embodiment includes a quartz tuning fork 101, a probe 102, a microwave radiation module 103, a fluorescence acquisition module 104, a processing module 105, and a sample to be tested 106.

[0027] A quartz tuning fork 101 is movably disposed relative to the upper surface of the sample to be tested and configured to perform simple harmonic motion along a first direction, wherein the first direction is perpendicular to the upper surface of the sample 106. The first direction can be vertical. Simple harmonic motion is a periodic vibration model. It describes the idealized motion of a system when subjected to a restoring force proportional to the displacement and always pointing towards the equilibrium position.

[0028] The quartz tuning fork 101 is a tiny, tuning fork-shaped quartz crystal (typically a few millimeters long). Its two "fork teeth" undergo very stable and high-Q (high mechanical quality factor) periodic bending vibrations when an electric current is applied. For example, the quartz tuning fork 101 can be placed on the upper surface of a sample to be tested, and by applying a specific alternating voltage to the quartz tuning fork 101, the "fork teeth" of the quartz tuning fork 101 will perform simple harmonic vibrations in the vertical direction perpendicular to the upper surface of the sample to be tested.

[0029] The probe 102 is fixedly disposed on the lower surface of the quartz tuning fork 101 and configured to perform simple harmonic oscillation along a first direction with the quartz tuning fork. The probe contains an NV color center. The method of fixing the probe 102 to the lower surface of the quartz tuning fork 101 includes, but is not limited to, bonding with ultraviolet curable adhesive, soldering, focused ion beam deposition, or integration methods.

[0030] The microwave radiation module 103 is configured to emit microwave pulses to the probe 102 when the probe 102 is at the highest or lowest point of the simple harmonic vibration, so that the NV color center accumulates phase information.

[0031] The microwave radiation module can be moved close to the diamond probe within a micrometer range using a micrometer-scale translation stage, outputting microwave pulses (e.g., 2.87 GHz) with a frequency matching the resonant frequency of the NV center. This allows for testing of the NV center fluorescence response, confirming that microwaves can effectively manipulate spin quantum states. For example, a microwave signal generator can be used to generate a frequency-tunable continuous microwave signal and emit it towards probe 102.

[0032] In the embodiments of this disclosure, a piezoelectric ceramic can be used to drive a quartz tuning fork and set the vibration frequency (greater than 100kHz). The charge amplifier amplifies the sinusoidal oscillation voltage signal accumulated by the quartz tuning fork into a sinusoidal voltage, which is then converted into a square wave signal by a comparator and transmitted to an arbitrary sequence generator, thus initially establishing a synchronous link between mechanical vibration and hardware control.

[0033] The fluorescence acquisition module 104 is configured to send a laser to the probe 102 and acquire the fluorescence excited by the NV color center to obtain a fluorescence signal, wherein the fluorescence signal carries the phase information accumulated by the NV color center.

[0034] The role of the laser is to initialize the spin state of the NV color center and read out its final quantum state. In embodiments of this disclosure, a continuous-wave laser or a pulsed laser can be used to send laser light to probe 102. The wavelength of the sent laser can be 532 nm (green) laser light, because the NV color center has high absorption efficiency for this wavelength, which can effectively excite electrons from the ground state to the excited state.

[0035] Since a microwave pulse needs to be emitted between the initialization of the spin state of the NV color center and the readout of its final quantum state to allow the NV color center to accumulate phase information, continuous laser light cannot be emitted during the microwave pulse emission. Therefore, in the embodiments of this disclosure, continuous laser light needs to be converted into laser pulses, and laser pulses for reading out the quantum state of the NV color center are applied before and after the microwave pulse signal based on precise timing control. In the embodiments of this disclosure, an acousto-optic modulator or an electro-optic modulator can be used to convert continuous laser light into laser pulses.

[0036] Fluorescence signals can be acquired using detectors such as avalanche photodiodes, single-photon counter modules, or photomultiplier tubes. The fluorescence acquisition module 104 sends a laser beam to the probe 102 and acquires the fluorescence signal returned by the NV color center through a detector. Fluorescence is the photon released when the NV color center transitions from an excited state back to its ground state; its intensity carries spin quantum state information, meaning the fluorescence brightness of the NV color center is directly related to its spin state.

[0037] The processing module 105 is configured to perform vector electric field imaging based on fluorescence signals.

[0038] The processing module 105 can convert fluorescence signal information into spin quantum state information of the NV color center, and obtain the electric field intensity at the location of the NV color center through the spin quantum state information.

[0039] In the embodiments of this disclosure, when the NV color center vibrates upward and downward, the energy level shifts caused by the Stark effect are in opposite directions. Therefore, the alternating electric field is measured using a spin echo sequence or a higher-order dynamic decoupling sequence such as XY8.

[0040] In embodiments of this disclosure, a flip pulse is applied at the moment when the NV color center is in the equilibrium position of mechanical vibration, thereby accumulating the maximum phase in quantum interference measurements.

[0041] In the embodiments of this disclosure, the frequency of mechanical vibration can be 180 kHz, and the frequency of quantum manipulation can be 10 MHz, achieving nanosecond-level time synchronization between mechanical vibration and quantum manipulation.

[0042] Through the embodiments of this disclosure, the NV color center can be manipulated to perform simple harmonic oscillations in the up-down direction on the upper surface of the sample under test. The electrostatic field around the sample under test is equivalent to an alternating electric field in the coordinate system of the NV color center. When the frequency of the alternating electric field is higher than the shielding frequency, the equivalent alternating electric field can be measured, thereby overcoming the problem of the low intensity of the electric field signal sensed by the NV color center and improving the resolution of vector electric field imaging.

[0043] According to an embodiment of the present disclosure, a nanometer-resolution vector electric field imaging device is provided with a differential electrode on a quartz tuning fork. The quartz tuning fork is configured to provide piezoelectric charges generated during simple harmonic vibration to the differential electrode, wherein the polarity change period of the piezoelectric charges is consistent with the vibration period of the simple harmonic vibration.

[0044] The core working principle of a quartz tuning fork is the inverse piezoelectric effect and the direct piezoelectric effect. When a quartz tuning fork vibrates, its arms periodically bend and extend, generating periodic mechanical stress within the material. According to the direct piezoelectric effect, this stress directly induces an alternating piezoelectric charge on the tuning fork electrodes. The frequency of this electrical signal is strictly synchronized with the vibration frequency of the tuning fork; that is, the period of polarity change of the piezoelectric charge coincides with the vibration period of simple harmonic motion.

[0045] Through the embodiments of this disclosure, piezoelectric charges generated by electrodes with a polarity change period consistent with the vibration period of simple harmonic motion can be used to convert the mechanical vibration information of a quartz tuning fork into charge information for subsequent quantum manipulation, thereby achieving nanosecond-level synchronization between the mechanical oscillator and quantum manipulation.

[0046] The nanoscale resolution vector electric field imaging device according to embodiments of this disclosure may further include a control module. The control module is electrically connected to a differential electrode and configured to acquire piezoelectric charges to obtain a sinusoidal oscillating voltage signal. Based on the sinusoidal oscillating voltage signal and target time delay information, it provides a first pulse control signal to a microwave radiation module and a second pulse control signal to a fluorescence acquisition module. The microwave radiation module is configured to emit microwave pulses to the probe under the control of the first pulse control signal to modulate the electron spin state of the NV color center, thereby accumulating phase information at the NV color center. Under the control of the second pulse control signal, the fluorescence acquisition module sends a laser beam to the probe and acquires the fluorescence excited by the NV color center to obtain a fluorescence signal.

[0047] An electrical connection refers to establishing a path between two or more electronic components, circuit nodes, or physical systems through conductors and connectors, allowing the controlled flow of electric charge and signals. Piezoelectric charge is generated by the vibration of a quartz tuning fork, and the period of polarity change of the piezoelectric charge coincides with the period of simple harmonic vibration. Because signal transmission between different modules takes time, there is a certain delay in the time information of signals between different modules. Therefore, it is necessary to obtain time delay information to compensate for hardware delays and subsequent signal measurements, ensuring the realization of quantum coherent sensing that synchronizes mechanical oscillators and quantum manipulation.

[0048] In the embodiments of this disclosure, the piezoelectric sinusoidal oscillating voltage signal is converted into a pulse control signal with a fixed pulse width and amplitude. This can be based on the zero-crossing detection method of a comparator, the peak detection and comparison method, or the digital processing method of a microcontroller, etc.

[0049] Figure 2 A schematic diagram of the control module of a nanometer-resolution vector electric field imaging apparatus according to an embodiment of the present disclosure is shown.

[0050] like Figure 2As shown, the charge accumulated by the mechanical oscillation of the quartz tuning fork 201 is amplified into a voltage signal by the charge amplifier 202, generating a sinusoidal oscillating voltage with the same frequency as the mechanical vibration of the charged quartz tuning fork 201. This voltage is then converted into a square wave signal by the comparator 203. The arbitrary sequence generator 204 outputs control pulses with nanosecond-level control precision to synchronize all hardware, including the movement of the displacement stage, the switching of the acousto-optic modulator, the frequency, amplitude, and phase control of the microwave radiation module, the switching of the microwave radiation module, the data acquisition of the fluorescence acquisition module, and delay alignment. The arbitrary sequence generator 204 is triggered by the level converted by the comparator 203 or by the rising or falling edge, and by adjusting the delay alignment time, it can achieve time synchronization of quantum sensor control related to the mechanical vibration of the quartz tuning fork 201, the switching of the acousto-optic modulator, the frequency, amplitude, and phase control of the microwave radiation module, the switching of the microwave radiation module, and the data acquisition of the fluorescence acquisition module at the nanosecond scale, thus realizing quantum coherent sensing that synchronizes the mechanical oscillator and quantum control.

[0051] The specific implementation methods of the microwave radiation module and the fluorescence acquisition module are as described above and will not be repeated here.

[0052] Through the embodiments of this disclosure, a first pulse control signal and a second pulse control signal can be provided based on the piezoelectric sinusoidal oscillation voltage signal and the target time delay information, and used for the timing control of the microwave radiation module and the fluorescence acquisition module, thereby achieving nanosecond-level synchronization between the mechanical oscillator and quantum manipulation.

[0053] The control module of the nanoscale resolution vector electric field imaging apparatus according to embodiments of the present disclosure may include a charge amplifier, a comparator, a sequence generator, and a delay alignment unit.

[0054] The charge amplifier is configured to amplify the piezoelectric charge accumulated by the quartz tuning fork into a sinusoidal oscillating voltage signal. Because the piezoelectric charge output by the quartz tuning fork is weak, easily attenuated, and susceptible to interference, it is necessary to amplify the piezoelectric charge.

[0055] The comparator is configured to convert a sinusoidal oscillating voltage signal into a square wave signal.

[0056] A sequence generator is configured to generate a first control signal and a second control signal based on a square wave signal and a control timing sequence.

[0057] Control timing is a set of time control logic predefined in order to ensure the precise and coordinated operation of various functional modules during vector electric field imaging.

[0058] In the embodiments of this disclosure, a piezoelectric ceramic can be used to drive a quartz tuning fork and set the vibration frequency (greater than 100kHz). The charge amplifier amplifies the sinusoidal oscillation voltage signal accumulated by the quartz tuning fork into a sinusoidal voltage, which is then converted into a square wave signal by a comparator and transmitted to an arbitrary sequence generator, thus initially establishing a synchronous link between mechanical vibration and hardware control.

[0059] The delay alignment unit is configured to process the first control signal and the second control signal based on the target delay information to obtain the first pulse control signal and the second pulse control signal, and to provide the first pulse control signal to the microwave radiation module and the second pulse control signal to the fluorescence acquisition module.

[0060] The target delay information is the optimal delay time parameter, under which the phase magnitude accumulated by the NV color center is the largest.

[0061] Through the embodiments of this disclosure, precise timing logic control of the microwave radiation module and the fluorescence acquisition module can be performed based on the delay alignment unit under the optimal delay parameters to obtain the phase signal of the NV color center accumulation, thereby achieving high-resolution electric field imaging.

[0062] Figure 3 The illustration schematically shows a synchronous measurement sequence of a nanometer-resolution vector electric field imaging apparatus according to an embodiment of the present disclosure.

[0063] like Figure 3 As shown, firstly, the fluorescence acquisition module emits a laser to irradiate the NV color center, initializing it to a defined ground state; then, a synchronization operation is performed to ensure that each module achieves synchronized control; subsequently, the microwave radiation module emits a microwave pulse signal to modulate the electron spin state of the NV color center, allowing the NV color center to accumulate phase information; then, the fluorescence acquisition module emits a laser and acquires the fluorescence excited by the NV color center; simultaneously, photon acquisition and counting are performed to obtain the total number of fluorescent photons.

[0064] According to embodiments of this disclosure, determining the target time delay information before performing vector electric field imaging of the sample under test can be achieved by configuring the delay alignment unit and processing module as follows:

[0065] The delay alignment unit is configured to obtain multiple first pulse control test signals and multiple second pulse control test signals based on multiple preset delay information, a first control signal, and a second control signal.

[0066] The processing module is configured to receive multiple fluorescence test signals returned by the fluorescence acquisition module under the control of multiple first pulse control test signals and multiple second pulse control test signals, and obtain multiple test populations based on the multiple fluorescence test signals and the target amplitude of the NV color center. It then fits and determines the target test population from the multiple test populations and determines the preset time delay information related to the target test population as the target time delay information.

[0067] The target delay information is the optimal delay time parameter, at which the phase magnitude accumulated by the NV color centers is maximized. Population specifically refers to the probability or proportion of NV color centers in a particular spin state.

[0068] For example, a spin echo sequence can be applied, and the delay time t can be adjusted by a delay alignment unit. Each delay time value corresponds to a preset delay information and a set of first pulse control test signals and second pulse control test signals. The processing module receives a set of first pulse control test signals and second pulse control test signals and obtains the corresponding fluorescence test signals. Multiple delay times correspond to multiple fluorescence test signal results. Based on multiple test populations, normalized signals under different delays are determined, with phase... A signal curve is obtained by fitting the signal to the horizontal axis and the normalized signal to the vertical axis. The phase corresponding to the maximum signal amplitude is determined, and the delay time t at this point is recorded and used as the optimal delay parameter. The length of the delay is varied. Equivalent to change The size of , and their relationship is as follows: , The frequency of mechanical vibration.

[0069] Through the embodiments of this disclosure, target time delay information can be obtained, thereby calibrating key parameters of electric field imaging and improving the accuracy of electric field gradient measurement.

[0070] The vector electric field imaging apparatus according to embodiments of the present disclosure further includes a displacement stage.

[0071] The displacement stage is configured to adjust the positions of the quartz tuning fork and the sample to be tested, so as to adjust the probe to a preset distance from the first surface of the sample to be tested; wherein, the preset distance is configured so that the NV color center of the probe is in the electric field of the first surface of the sample to be tested during simple harmonic oscillation.

[0072] For example, a MoS2 thin film is placed on a displacement stage as the sample to be tested. The sample position is coarsely adjusted using the displacement stage so that the upper surface of the MoS2 thin film is aligned with the bottom of a diamond probe. The preset distance can be on the order of hundreds of micrometers; for example, the distance between the probe and the upper surface of the sample can be 100 micrometers, 200 micrometers, or 300 micrometers, etc. At the above preset distance, during the simple harmonic oscillation of the NV color center of the probe, it remains within the electric field of the upper surface of the sample.

[0073] The displacement stage can perform nanoscale three-dimensional translation, scanning the sample imaging area point by point in a certain step. With each step, the distance between the probe and the sample is kept stable. That is, the distance is adjusted by using amplitude changes through the force feedback mode of the quartz tuning fork.

[0074] According to embodiments of this disclosure, determining the target amplitude of the NV color center before performing vector electric field imaging of the sample to be tested can be achieved by configuring the displacement stage and processing module as follows:

[0075] The displacement stage is configured to adjust the position of the quartz tuning fork so that the NV color center is at the half-width at half-maximum of the point spread function, which is determined by confocal scanning of the NV color center along the first direction. The processing module is configured to collect multiple photon counts during the simple harmonic oscillation of the NV color center through the fluorescence acquisition module, and obtain the target amplitude of the NV color center based on the point spread function and the multiple photon counts.

[0076] For example, a confocal scan can be performed on the vibration direction of the NV color center to acquire the point spread function of the focused spot. The intensity distribution was recorded, spanning hundreds of micrometers laterally and several micrometers longitudinally. The NV color center was moved using a displacement stage to position it at the half-width-height (FWHM) of the point spread function, where the maximum intensity gradient could be obtained. A first-order Taylor expansion of the point spread function at this position was then performed to obtain the photon count. With vibration position The linear relationship is:

[0077] (1)

[0078] in, It is the gradient. These are the coordinates of the vibration center point in the laboratory coordinate system. The background photon count is a known quantity and can be determined through static acquisition. Then, using an arbitrary sequence generator to synchronize tuning fork vibration and fluorescence acquisition, the time-domain photon counting curve of the NV color center's simple harmonic oscillation is obtained:

[0079] (2)

[0080] in, For the delay length, For mechanical vibration frequency, For amplitude, The vibrational phase is used. The maximum photon count is extracted based on the photon counting time-domain curve. and the minimum number of photons Substitute it into the following equation:

[0081] (3)

[0082] Thus, the amplitude A is calculated, which is the target amplitude of the NV color center.

[0083] The vector electric field imaging apparatus according to embodiments of the present disclosure further includes an electric field generation module.

[0084] The electric field generation module includes a first electrode, a second electrode, and a power supply. The first electrode is configured to be attached to the second surface of a quartz tuning fork, and the second electrode is configured to be positioned relative to the first electrode and is used to place the sample to be tested. The first electrode and the second electrode are respectively connected to the positive and negative terminals of the power supply to generate a uniform electric field on the first surface of the sample to be tested. The direction of the uniform electric field is consistent with the first direction.

[0085] Figure 4 A schematic diagram of a nanometer-resolution vector electric field imaging apparatus according to another embodiment of the present disclosure is shown.

[0086] like Figure 4 As shown, the vector electric field imaging device includes a quartz tuning fork 401, a fixed point 402, an upper electrode 403, a glass substrate 404, a probe 405, a lower electrode 406, and a power supply 407.

[0087] A quartz tuning fork 401 is used to generate vibrations in the experiment, with its amplitude or phase serving as feedback between the probe and the sample. The upper electrode 403 is connected to the power supply 407 via a fixing point 402. The upper electrode 403 and the glass substrate 404 together provide support and fixation. The glass substrate 404 is bonded to the probe 405 using UV adhesive. The probe 405 is a diamond with nanopillars etched onto its surface using micro-nano processing. The diamond NV color centers exist a few nanometers to tens of nanometers below the surface of the nanopillars, serving as a quantum sensing unit. The sample to be tested is placed on electrode 406, which is connected to the power supply 407. The power supply 407 is responsible for generating a uniform electric field in the range of hundreds of micrometers between the upper electrode 403 and electrode 406. The diamond is situated within this uniform electric field, approximately hundreds of micrometers in size and perpendicular to the sample surface, constructed by the upper electrode 403 and lower electrode 406. The upper electrode 403 can be connected to the power supply 407 via silver paste or by spot welding. The upper electrode 403 can be indium tin oxide conductive glass or other transparent electrodes. The lower electrode 406 can be a highly conductive silicon substrate. The diamond probe is situated in a uniform electric field, approximately 100 micrometers in size and perpendicular to the sample surface, constructed by the upper and lower electrodes. The magnitude of the uniform electric field around the probe 405 can be adjusted by regulating the voltage output; the range of uniformity is as follows: .

[0088] In the embodiments of this disclosure, the depth of the NV color center in the diamond probe is less than 20 nm, the vibration frequency of the quartz tuning fork is greater than 100 kHz, and the amplitude is less than 100 nm, which drives the quartz tuning fork carrying the NV color center to vibrate in a direction perpendicular to the sample surface, that is, vibrate in the z-axis direction of the displacement stage.

[0089] Optionally, after confirming the depth of the NV center of probe 405, the angle of probe 405 can be adjusted by a displacement stage and a two-dimensional tilting stage so that the vibration direction of the NV center is perpendicular to the sample surface. The indium tin oxide conductive glass is then connected to the power supply 407 through silver paste to construct a uniform electric field environment of "upper electrode-diamond-lower electrode".

[0090] The vector electric field imaging apparatus according to embodiments of the present disclosure further includes a magnetic field module.

[0091] The magnetic field module includes at least one magnet configured to surround the probe along a second direction. The magnetic field module is configured to provide a polarization magnetic field to the probe to modulate the NV color center into an electrical measurement state using the deflection magnetic field.

[0092] In embodiments of this disclosure, the second direction can be a direction parallel to the upper surface of the sample to be tested, or a direction that is not parallel to the upper surface of the sample to be tested.

[0093] For example, the position of the magnet can be adjusted by a micron-level translation stage so that the magnet is parallel to the upper surface of the sample and surrounds the probe. A magnetic field with a magnitude greater than 4 mT perpendicular to the symmetry axis of the NV color center can be applied. The eigenlevel of the NV color center can be calibrated by Zeeman splitting to ensure that the ground state spin quantum state can be controlled by microwaves.

[0094] The processing module of the vector electric field imaging apparatus according to embodiments of this disclosure can be configured as follows:

[0095] Based on the fluorescence signal and the target amplitude of the NV color center, the first population associated with the first coherent state and the second population associated with the second coherent state are determined; based on the first population and the second population, the electric field gradient value of the current scanning point is determined; and based on the electric field gradient values ​​of multiple scanning points, the vector electric field imaging result is obtained.

[0096] For example, at each scanning point, the control module outputs a synchronization pulse based on the optimal delay parameters; the fluorescence acquisition module emits a laser to irradiate the NV color center, initializes the NV color center, and puts it in a defined ground state; the microwave radiation module outputs a spin echo sequence to regulate the electronic spin state of the NV color center; the fluorescence acquisition module performs photon acquisition and records the number of fluorescent photons in the |0> and |1> states, thereby determining the population.

[0097] In embodiments of this disclosure, the synchronization delay can be changed, a spin echo or a higher-order dynamic decoupling sequence can be applied, and quantum state tomography can be used to read out the phase magnitude of the accumulated NV color centers.

[0098] In embodiments of this disclosure, the quantum state can be read out based on a microwave π / 2 pulse with the same phase as the spin echo, referred to in this disclosure as a cos measurement, or it can be read out based on a microwave π / 2 pulse with a 90° phase difference from the spin echo, referred to in this disclosure as a sin measurement.

[0099] Optionally, in the cosine measurement, the first population associated with the first coherent state can be obtained by the following formula:

[0100] (4)

[0101] in The shift of the energy level difference of the NV color center under the influence of an electric field. The vibration frequency of the probe, This represents the total evolution time in the spin echo or dynamic decoupling sequence. This corresponds to the phase of mechanical oscillation.

[0102] The second population associated with the second coherent state can be expressed by the following formula:

[0103] (5)

[0104] Based on the above results, in order to counteract the effects of fluorescence and coherence changes, the first and second populations need to be normalized as follows:

[0105] (6)

[0106] Based on the normalized signal formula of the cosine measurement and combined with known parameters, the NV color center energy level offset at each scan point is calculated. ; and then according to The linear relationship between the electric field gradient and the electric field gradient is used to calculate the electric field gradient value at each point, where the linear relationship is determined by the Stark effect coefficient of the NV color center.

[0107] Optionally, in the sin measurement, the first population associated with the first coherent state can be obtained by the following formula:

[0108] (7)

[0109] The second population associated with the second coherent state can be expressed by the following formula:

[0110] (8)

[0111] Based on the above results, in order to counteract the effects of fluorescence and coherence changes, the first and second populations need to be normalized as follows:

[0112] (9)

[0113] Based on the normalized signal formula of sin measurement and combined with known parameters, the NV color center energy level offset at each scan point is calculated. ; and then according to The linear relationship between the electric field gradient and the electric field gradient is used to calculate the electric field gradient value at each point. The linear relationship is determined by the Stark effect coefficient of the NV color center.

[0114] The vector electric field imaging results can be obtained based on the electric field gradient values ​​of multiple scanning points as follows:

[0115] The electric field gradient values ​​of all scanning points are mapped according to their spatial locations to generate an electric field gradient distribution image. Combined with the electric field direction annotation, which marks the vector direction and magnitude, a nanometer-resolution vector electric field image is finally output. When the resolution is 10 nm, the electric field gradient changes at the edge of the two-dimensional material can be clearly observed.

[0116] Figure 5 A schematic diagram of a nanometer-resolution vector electric field imaging apparatus according to another embodiment of the present disclosure is shown.

[0117] like Figure 5As shown, the nanoscale resolution vector electric field imaging device according to this embodiment includes a quartz tuning fork 101, a probe 102, a microwave radiation module 103, a fluorescence acquisition module 104, a processing module 105, a sample to be tested 106, a control module 107, a displacement stage 108, an electric field generation module 109, and a magnetic field module 110.

[0118] The quartz tuning fork 101, probe 102, microwave radiation module 103, fluorescence acquisition module 104, processing module 105, and sample to be tested 106 are as described above and will not be repeated here.

[0119] The control module 107 includes a charge amplifier configured to amplify the piezoelectric charge accumulated in the quartz tuning fork into a sinusoidal oscillating voltage signal; a comparator configured to convert the sinusoidal oscillating voltage signal into a square wave signal; a sequence generator configured to generate a first control signal and a second control signal based on the square wave signal and the control timing; and a delay alignment unit configured to process the first control signal and the second control signal based on the target delay information to obtain a first pulse control signal and a second pulse control signal, and to provide the first pulse control signal to the microwave radiation module and the second pulse control signal to the fluorescence acquisition module.

[0120] The displacement stage 108 is configured to adjust the position of the quartz tuning fork and the sample to be tested, so as to adjust the probe to a preset distance from the first surface of the sample to be tested; wherein, the preset distance is configured so that the NV color center of the probe is in the electric field of the first surface of the sample to be tested during simple harmonic oscillation.

[0121] The electric field generation module 109 includes a first electrode, a second electrode, and a power supply. The first electrode is configured to be attached to the second surface of a quartz tuning fork, and the second electrode is configured to be positioned relative to the first electrode and is used to place the sample to be tested. The first electrode and the second electrode are respectively connected to the positive and negative terminals of the power supply to generate a uniform electric field on the first surface of the sample to be tested. The direction of the uniform electric field is consistent with the first direction.

[0122] The magnetic field module 110 includes at least one magnet configured to surround the probe along a second direction. The magnetic field module is configured to provide a polarization magnetic field to the probe to modulate the NV color center into an electrical measurement state using the deflection magnetic field, wherein the second direction is a direction parallel to the first surface of the sample to be measured.

[0123] Those skilled in the art will understand that the features described in the various embodiments of this disclosure can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. In particular, the features described in the various embodiments of this disclosure can be combined and / or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0124] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A nanometer-resolution vector electric field imaging device, comprising: A quartz tuning fork is movably disposed relative to the upper surface of the sample to be tested and configured to perform simple harmonic motion along a first direction, wherein the first direction is perpendicular to the upper surface of the sample to be tested. A probe is fixedly disposed on the lower surface of the quartz tuning fork and configured to perform simple harmonic oscillations along the first direction with the quartz tuning fork, wherein the probe is equipped with an NV color center; A microwave radiation module is configured to emit microwave pulses to the probe when the probe is at the highest or lowest point of the simple harmonic vibration, so that the NV color center accumulates phase information. A fluorescence acquisition module is configured to send a laser to the probe and acquire the fluorescence excited by the NV color center to obtain a fluorescence signal, wherein the fluorescence signal carries the phase information accumulated by the NV color center; and The processing module is configured to perform vector electric field imaging based on the fluorescence signal.

2. The nanometer-resolution vector electric field imaging device according to claim 1, wherein, The quartz tuning fork is provided with a differential electrode, and the quartz tuning fork is configured to provide the piezoelectric charge generated during the simple harmonic motion to the differential electrode, and the polarity change period of the piezoelectric charge is consistent with the vibration period of the simple harmonic motion.

3. The nanometer-resolution vector electric field imaging device according to claim 2 further comprises: The control module, electrically connected to the differential electrode, is configured to acquire piezoelectric charges, obtain a sinusoidal oscillating voltage signal, and, based on the sinusoidal oscillating voltage signal and target time delay information, provide a first pulse control signal to the microwave radiation module and a second pulse control signal to the fluorescence acquisition module. The microwave radiation module is configured to emit microwave pulses to the probe under the control of the first pulse control signal, so as to regulate the electron spin state of the NV color center and accumulate phase information of the NV color center. Under the control of the second pulse control signal, the fluorescence acquisition module sends a laser to the probe and acquires the fluorescence excited by the NV color center to obtain a fluorescence signal.

4. The nanometer-resolution vector electric field imaging device according to claim 3, wherein, The control module includes: A charge amplifier configured to amplify the piezoelectric charge accumulated in the quartz tuning fork into the sinusoidal oscillating voltage signal; A comparator is configured to convert the sinusoidal oscillating voltage signal into a square wave signal; A sequence generator, configured to generate a first control signal and a second control signal based on the square wave signal and a control timing sequence; and The delay alignment unit is configured to process the first control signal and the second control signal based on the target delay information to obtain the first pulse control signal and the second pulse control signal, and to provide the first pulse control signal to the microwave radiation module and the second pulse control signal to the fluorescence acquisition module.

5. The nanometer-resolution vector electric field imaging device according to claim 4, wherein, Before performing vector electric field imaging of the sample under test, The delay alignment unit is configured to obtain multiple first pulse control test signals and multiple second pulse control test signals based on multiple preset delay information, the first control signal and the second control signal; The processing module is configured to receive multiple fluorescence test signals returned by the fluorescence acquisition module under the control of the multiple first pulse control test signals and the multiple second pulse control test signals, and obtain multiple test populations based on the multiple fluorescence test signals and the target amplitude of the NV color center, fit and determine a target test population from the multiple test populations, and determine the preset time delay information related to the target test population as the target time delay information.

6. The nanometer-resolution vector electric field imaging device according to claim 1, further comprising: The displacement stage is configured to adjust the positions of the quartz tuning fork and the sample to be tested, so as to adjust the probe to a preset distance from the first surface of the sample to be tested; The preset distance is configured such that the NV color center of the probe is in the electric field of the first surface of the sample under test during simple harmonic vibration.

7. The nanometer-resolution vector electric field imaging device according to claim 6, wherein, Before performing vector electric field imaging of the sample under test, The displacement stage is configured to adjust the position of the quartz tuning fork so that the NV color center is at the half-width at half-maximum of the point spread function, wherein the point spread function is determined by confocal scanning of the NV color center along the first direction. The processing module is configured to acquire multiple photon counts during the simple harmonic oscillation of the NV color center using the fluorescence acquisition module, and to obtain the target amplitude of the NV color center based on the point spread function and the multiple photon counts.

8. The nanometer-resolution vector electric field imaging device according to claim 1, further comprising: An electric field generation module includes a first electrode, a second electrode, and a power supply. The first electrode is configured to be attached to the second surface of the quartz tuning fork, and the second electrode is configured to be positioned relative to the first electrode. The second electrode is used to place the sample to be tested. The first electrode and the second electrode are connected to the positive and negative terminals of the power supply, respectively, to generate a uniform electric field on the first surface of the sample to be tested. The direction of the uniform electric field is consistent with the first direction.

9. The nanometer-resolution vector electric field imaging device according to claim 1, further comprising: A magnetic field module includes at least one magnet, the at least one magnet being configured to surround the probe along a second direction, the magnetic field module being configured to provide a polarization magnetic field to the probe to modulate the NV color center into an electrical measurement state using the deflection magnetic field.

10. The nanometer-resolution vector electric field imaging device according to claim 1, wherein, The processing module is configured as follows: Based on the fluorescence signal and the target amplitude of the NV color center, determine the first population associated with the first coherent state and the second population associated with the second coherent state; Based on the first population and the second population, the electric field gradient value of the current scanning point is determined; as well as Vector electric field imaging results are obtained based on the electric field gradient values ​​of multiple scanning points.

Images