Integrated equipment for representing nitrogen vacancy color center quantum characteristics and sensing sensitivity

Abstract

The invention relates to the technical field of quantum sensing and optical instruments, and discloses integrated equipment for representing nitrogen vacancy color center quantum characteristics and sensing sensitivity, which comprises a laser module, an inverted optical microscope module, an electronic control and data acquisition module and a system software control module, the laser module realizes continuous laser beam output or pulse laser beam output through light path selection; the inverted optical microscope module receives the laser beam and collects the nitrogen vacancy color center of the sample, and selectively guides fluorescence to the confocal single photon counting branch or the analog signal detection branch through the light path selection mechanism; the electronic control and data acquisition module is responsible for driving each device and processing signals from different detection branches; and the system software control module cooperates with each module to execute quantum characteristic characterization and sensing sensitivity evaluation tasks. Through deep integration of software and hardware, dual-mode measurement is realized on a single platform, and the device has the advantages of high function integration level, compact structure, convenience in operation and high measurement efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of quantum sensing and optical instruments, in particular to an integrated device for characterizing quantum properties and sensing sensitivity of nitrogen vacancy color centers. BACKGROUND

[0002] Due to its long quantum coherence time, optical polarization and readout at room temperature, diamond nitrogen vacancy (NV) color center is considered as an ideal platform for realizing high-sensitivity magnetic field, electric field, temperature and stress sensors. In the process of NV color center quantum sensor from laboratory research to industrial application, accurate and efficient characterization of quantum properties and actual sensing performance of diamond NV color center material is a key link.

[0003] However, the existing devices for NV color center characterization still have certain limitations. On the one hand, traditional quantum property characterization devices, such as pulse confocal systems for measuring quantum coherence characteristic parameters of NV color center such as lifetime, Rabi oscillation, Ramsey interference and Hahn echo, often require complex free-space optical path setup and precise timing control, resulting in a large device volume, which usually needs to be fixedly deployed in a special optical laboratory environment, limiting the flexibility of its application scenarios.

[0004] On the other hand, current commercial NV color center characterization devices are relatively single in function. Most devices can measure NV color center concentration and quantum property time parameters, but generally lack the ability to directly characterize sensing sensitivity of magnetic field, temperature, etc. When quantum properties and sensing sensitivity need to be evaluated at the same time, researchers often need to use two independent devices or manually reconfigure the hardware optical path and replace the detector of the same device. This separation or manual reconfiguration not only greatly reduces the experimental efficiency and increases the operation complexity, but also makes it difficult to ensure that the two measurements are performed under completely consistent experimental conditions, thereby affecting the accuracy and comparability of the data results, which is not conducive to comprehensive and consistent performance evaluation and optimization of NV color center materials. Therefore, the industry urgently needs a device that can realize dual characterization of NV color center quantum properties and sensing sensitivity on a single platform, and has the characteristics of miniaturization, integration and automation. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides an integrated device for characterizing quantum properties and sensing sensitivity of nitrogen vacancy color centers, aiming to solve the problems of low measurement efficiency, complicated operation and difficulty in ensuring data consistency caused by the large volume and single function of the characterization device in the prior art when measuring two different types of quantum properties and sensing sensitivity.

[0006] In order to achieve the above object, the present application is implemented by the following technical solutions: an integrated device for characterizing quantum properties and sensing sensitivity of nitrogen vacancy color centers, comprising: a laser module, which comprises a laser, a power and polarization adjustment unit composed of a half-wave plate and a polarization beam splitting cube, an acousto-optic modulator, and a fiber coupler.

[0007] an inverted optical microscope module, which comprises a fiber coupling head, a number of cage system mirrors, a high-pass dichroic mirror, an objective lens, and a light path selection mechanism.

[0008] an electronic control and data acquisition module, which is used to provide driving signals to active devices in the laser module and the inverted optical microscope module, and receive and process signals from the detection branches.

[0009] a system software control module, which runs on a computer and is used to cooperatively control the aforementioned modules to perform corresponding measurement processes according to a quantum property characterization task or a sensing sensitivity evaluation task selected by a user.

[0010] Preferably, when the pulsed laser beam is generated, the laser beam is guided to the acousto-optic modulator by a plane mirror, and the electronic control and data acquisition module applies a radio frequency driving signal to the acousto-optic modulator to diffract the laser beam, and an aperture is used to selectively allow the first-order diffracted beam to pass through.

[0011] Preferably, when the continuous laser beam is generated, the laser beam is guided by a plane mirror to bypass the acousto-optic modulator and directly enter the fiber coupler.

[0012] Preferably, the light path selection mechanism comprises at least one rotatable mirror and a beam splitter. By placing the rotatable mirror in the fluorescence light path, the fluorescence can be reflected to a camera for imaging.

[0013] Further, when the rotatable mirror is removed from the light path, the fluorescence enters a confocal single photon counting branch composed of a confocal collection system, which comprises at least two plano-convex lenses and a confocal pinhole, and is finally detected by a single photon counter.

[0014] Preferably, through the light path selection mechanism, the fluorescence is guided to an analog signal detection branch, which includes a plano-convex lens and a photodetector, and the photodetector converts the fluorescence intensity into an analog voltage signal and outputs it to a lock-in amplifier in the electronic control and data acquisition module.

[0015] Preferably, the inverted optical microscope module further comprises a sample displacement stage and an external magnetic field application system. The sample displacement stage is used to carry and accurately position the sample. The external magnetic field application system includes a magnet, a magnet holder and a magnet displacement stage, which is used to adjust the magnetic field applied to the sample.

[0016] Preferably, when performing a quantum characteristic characterization task, the electronic control and data acquisition module comprises a timing control core for generating a synchronized pulse sequence to control the on-off of the acousto-optic modulator, the microwave field, and the gating of the single photon counter for counting within a certain time window.

[0017] Preferably, when performing a sensing sensitivity evaluation task, the electronic control and data acquisition module comprises a microwave source and a lock-in amplifier, the microwave source generates a low-frequency modulation signal to frequency-modulate the microwave source, and the lock-in amplifier uses the low-frequency modulation signal as a reference signal to demodulate the signal from the photodetector.

[0018] Preferably, the device is built on an optical breadboard. The laser module is packaged in a laser control system box, and the inverted optical microscope module is packaged in an optical microscope box, and each module is supported and fixed by a stand.

[0019] The present application provides an integrated device for characterizing nitrogen vacancy color center quantum characteristics and sensing sensitivity. It has the following advantages: 1. The present application optimizes the overall layout of the device by packaging the laser module in a laser control system box and the inverted optical microscope module in a main system box, and fixing them on an optical breadboard. This design reduces the physical size to a desktop specification, solves the problem of large size of existing devices and the need for fixed deployment, and improves the portability of the device and the flexibility of the application scenario.

[0020] 2. The present application integrates quantum characteristic characterization and quantum sensing sensitivity evaluation functions. Through the light path design of the laser module that can selectively bypass the acousto-optic modulator, and the fluorescence detection light path switching mechanism realized by the rotatable mirror in the inverted optical microscope module, the device can quickly switch to the pulse measurement mode supported by the single photon counter or the continuous wave lock-in measurement mode supported by the photodetector without hardware reconstruction. This design greatly improves the characterization efficiency and ensures that different types of data are obtained under the same experimental conditions, ensuring the consistency of the results.

[0021] 3、The present application controls the system software control module and the electronic control and data acquisition module to work together, the electronic control and data acquisition module can automatically generate the complex pulse sequence for quantum characteristic characterization or generate the phase-locked amplification and sweep control signal for sensing sensitivity evaluation according to the measurement task; the design simplifies the device operation, reduces the dependence on the operator, and improves the stability and repeatability of the measurement results due to the reduction of manual intervention. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is the structure explosion drawing of the laser module of the present application; Figure 2 It is the structure schematic diagram of the diaphragm of the present application; Figure 3 It is the structure explosion drawing of the inverted optical microscope module of the present application; Figure 4 It is the structure schematic diagram of the optical fiber coupling head of the present application; Figure 5 It is the structure schematic diagram of the electronic control and data acquisition module of the present application; Figure 6 It is the structure schematic diagram of the drive box of the present application; Figure 7 It is the assembly schematic diagram of the sample to be measured and the microwave radiator of the present application; Figure 8 It is the effect schematic diagram of the experiment of the present application.

[0023] 1, column; 2, optical faceplate; 3, laser control system box; 4, laser; 5, half-wave plate; 6, polarization beam splitting cube; 7, plane mirror; 8, acousto-optic modulator; 9, diaphragm; 10, optical fiber coupler; 11, optical microscope box; 12, confocal pinhole; 13, single photon counter; 14, rotatable mirror; 15, camera; 16, magnet; 17, magnet holder; 18, magnet displacement table; 19, sample clamp; 20, sample displacement table; 21, objective lens; 22, cage system mirror; 23, high-pass dichroic mirror; 24, beam splitter; 25, optical fiber coupling head; 26, confocal collection system; 27, plano-convex lens. DETAILED DESCRIPTION

[0024] The specific embodiments of the present application are further described in detail below in combination with the drawings and examples.

[0025] Referring to the drawings Figure 1 - the drawings Figure 7The embodiment of the present application provides a kind of nitrogen vacancy color center quantum characteristic and sensing sensitivity characterization integrated equipment, the integrated equipment is built on optical breadboard 2 as a whole, and is fixed by mechanical support components such as stand 1, to ensure the stability of system.The equipment mainly includes: laser module, inverted optical microscope module, electronic control and data acquisition module, and system software control module.

[0026] The function of laser module is to generate and accurately regulate the laser for exciting NV color center, and laser module can output continuous laser or nanosecond pulse laser according to experimental requirements, and transmit laser to subsequent optical path through optical fiber.Laser module includes laser 4, laser control system box 3, half-wave plate 5, polarization beam splitting cube 6, plane mirror 7, acousto-optic modulator 8, diaphragm 9 and fiber coupler 10.

[0027] Inverted optical microscope module is integrated in an optical microscope box 11 as the core functional area of system.The function of inverted optical microscope module is to receive excitation laser and focus it to sample, carry and precisely position sample to be measured and external magnetic field source, while efficiently collecting the fluorescence signal emitted by NV color center, and guiding fluorescence signal to different detectors for analysis according to experimental purpose.

[0028] Inverted optical microscope module includes confocal pinhole 12, single photon counter 13, rotatable mirror 14, camera 15, magnet 16, magnet stand 17, magnet displacement table 18, sample clamp 19, sample displacement table 20, objective lens 21, cage system mirror 22, high-pass dichroic mirror 23, beam splitter 24, fiber coupling head 25, confocal collection system 26 and plano-convex lens 27.

[0029] Electronic control and data acquisition module is responsible for generating all the precise timing control signals, radio frequency signals and microwave signals required for experiment.Electronic control and data acquisition module simultaneously synchronously collects signals from optical detectors (such as single photon counter 13 and camera 15), realizes the automatic control of entire experimental process.

[0030] System software control module runs on external computer, and provides user operation interface through graphical user interface (GUI).The module can coordinate scheduling each instrument in electronic control module and optical module, execute experimental parameter configuration, and realize data acquisition, real-time visualization and subsequent processing.

[0031] The above modules work together, so that the present equipment can realize the whole process from sample excitation, signal collection to data analysis.

[0032] Refer to the drawings Figure 1The laser module is used to generate and control the light source required for exciting NV color centers, which includes a light source and a control unit, a power and polarization adjustment unit, a pulse modulation unit, and a fiber coupling unit.

[0033] In one embodiment, the laser module includes a laser 4, for example a solid-state laser with a wavelength of 532 nm, which is driven and monitored by a laser control system box 3. The electronic circuit in the laser control system box 3 ensures the stability of the output power and wavelength of the laser 4.

[0034] The continuous laser beam emitted from the laser 4 has a power and polarization adjustment unit in its optical path, which can be composed of a half-wave plate 5 and a polarization beam splitting cube 6. By rotating the angle of the half-wave plate 5, the polarization direction of the laser incident on the polarization beam splitting cube 6 can be changed. Since the polarization beam splitting cube 6 has different transmittance and reflectance for light with different polarization directions, rotating the half-wave plate 5 can continuously change the laser power passing through the polarization beam splitting cube 6, thereby achieving precise control of the excitation light power in the subsequent optical path.

[0035] To meet different characterization needs, the optical path of the laser module can be configured in at least two working modes. The optical path contains at least three plane mirrors 7.

[0036] In the first working mode, i.e. the pulse working mode, which is used to characterize the quantum properties of diamond NV color centers. The power-adjusted laser beam is guided by two plane mirrors 7 to a pulse modulation unit, which is used to convert continuous laser into pulsed laser. In one embodiment, the pulse modulation unit includes an acousto-optic modulator 8 (AOM, operating frequency 100 MHz, operating wavelength 532 nm) and an aperture 9. When performing experiments such as quantum coherence characterization that require pulsed excitation, the electronic control and data acquisition module applies a 100 MHz radio frequency drive signal to the acousto-optic modulator 8, causing the laser beam to diffract. The aperture 9 is placed after the acousto-optic modulator 8, which functions to spatially selectively allow only the first-order diffracted beam to pass through, and blocks the zero-order undiffracted beam and other orders of diffracted light. By adjusting the angles of the plane mirrors 7 and the drive of the acousto-optic modulator 8, the diffraction efficiency of the first-order diffracted beam can reach about 48%. The first-order diffracted beam is then guided to the fiber coupling unit by another plane mirror 7.

[0037] In the second working mode, i.e. the continuous working mode, which is used to characterize the magnetic field sensitivity of NV color centers. By adjusting the optical path structure, for example, by removing one of the plane mirrors 7 in the optical path of the second working mode, the laser beam bypasses the acousto-optic modulator 8 and is directly guided to the fiber coupling unit by a plane mirror 7.

[0038] The fiber coupling unit in the present embodiment is embodied as one or more fiber couplers 10, such as a crystal optical model FAC2-532-APC coupler. Regardless of the working mode, the light beam is finally coupled into a 50-micron core diameter multi-mode fiber to stably transmit the laser to the subsequent inverted optical microscope module. By precisely adjusting the five-axis adjustment frame that fixes the fiber coupler 10, the fiber coupling efficiency can reach about 85% in both working modes.

[0039] Referring to the drawings Figure 2 The inverted optical microscope module, as the core functional area of the system, integrates the functions of sample excitation, sample and magnetic field manipulation, and multi-mode fluorescence detection in the optical microscope box 11 to achieve compact structure and stable performance.

[0040] In one specific embodiment, the fiber from the laser module is connected to the fiber coupling head 25 of the module. After collimation, the excitation laser emitted from the fiber coupling head 25 is incident to the high-pass dichroic mirror 23. The high-pass dichroic mirror 23 has the property of reflecting excitation light (e.g., 532 nm wavelength) and transmitting NV color center fluorescence with longer wavelength (e.g., greater than 650 nm). The reflected excitation light is guided via at least three cage system mirrors 22 and finally focused on the sample surface by the objective lens 21, such as a 50X, numerical aperture (NA) of 0.55, focal length of 4mm objective lens 21, forming a diffraction-limited size spot. The cage system mirrors 22 are used for precise adjustment of the optical path.

[0041] The inverted optical microscope module also includes a sample and magnetic field bearing and control unit. Specifically, the diamond sample to be measured is fixed by the sample clamp 19 and installed on the sample displacement stage 20. The sample displacement stage 20 is a three-dimensional displacement stage that can achieve micron or sub-micron level precision movement in three orthogonal directions, thereby being used for scanning on the sample, positioning specific NV color centers, and accurately adjusting the focal plane. At the same time, the inverted optical microscope module is also provided with an external magnetic field application system, which is composed of a magnet 16 (e.g., a permanent magnet with a size of 20mm x 20mm x 20mm), a magnet holder 17 for fixing the magnet 16, and a magnet displacement stage 18. The magnet displacement stage 18 can be another manual micron displacement stage. By adjusting the magnet displacement stage 18, the relative position and angle between the magnet 16 and the sample can be accurately changed, thereby controlling the magnetic field strength applied to the NV color center axis.

[0042] The core feature of the inverted optical microscope module is its inclusion of a multi-modal fluorescence collection and detection optical path. The fluorescence generated by the NV color centers upon excitation is collected by the same objective 21. The collected fluorescence propagates in the reverse direction of the excitation light path, passing through at least three cage system mirrors 22 and a high-pass dichroic mirror 23 in sequence. At this point, most of the excitation light is filtered out by the high-pass dichroic mirror 23. Additional long-pass filters (e.g. a 650 nm cut-off filter) can be further included in the optical path to completely eliminate the residual excitation light. The clean fluorescence signal then impinges on an optical path selection mechanism, which allows the fluorescence to be directed to one of at least three functionally distinct detection branches, enabling a variety of measurement tasks to be performed without the need for hardware reconfiguration.

[0043] In one embodiment, the optical path selection mechanism can be composed of at least one rotatable mirror 14 and / or a beamsplitter 24, and the inverted optical microscope module includes four plano-convex lenses 27, one with a focal length of 100 mm and three with a focal length of 30 mm, which play a role in the different detection branches.

[0044] When the imaging detection branch is selected, the rotatable mirror 14 is placed in the optical path to reflect the fluorescence to an imaging optical train composed of a plano-convex lens 27 with a focal length of 100 mm. The imaging optical train works in conjunction with the beamsplitter 24 to image the fluorescence from the sample surface onto the photosensitive element of a camera 15. This branch is used for wide-field imaging of the sample, for observing the sample surface topography, and for assisting in the alignment of the laser spot and microwave antenna.

[0045] When the confocal single photon counting branch is selected, the rotatable mirror 14 is removed from the optical path, so that the fluorescence propagates in a straight line into the confocal collection system 26, passes through a plano-convex lens 27 with a focal length of 30 mm, is converged and shot to the confocal pinhole 12; the fluorescence signal passes through the confocal pinhole 12, and the spatial filtering effect of the pinhole can effectively suppress all stray fluorescence from the area outside the focal plane, which is the key to improving the signal-to-noise ratio and the Z-axis spatial resolution. The pure fluorescence signal passing through the pinhole is then converted into parallel light by a second plano-convex lens 27 with a focal length of 30 mm, and is recollimated into a parallel light beam. In the above parallel light path, the application particularly designs a replaceable filter slot, which is used to selectively insert different optical density attenuation sheets according to actual measurement needs, greatly widening the dynamic response range of the device, so that it can not only detect the weak signal of single NV color center, but also accurately characterize the strong fluorescence signal of high-concentration ensemble samples. After the intensity adjustment of the parallel fluorescence beam, it is coupled into a multimode optical fiber (such as a multimode optical fiber with a model of FCM1-PC-50L of Jingxi Optics) through a third plano-convex lens 27 with a focal length of 30 mm, and the optical fiber is connected to a single photon counter 13 (i.e. a single photon detector) through a fiber flange (such as a fiber flange with a model of FAA-SM1-APC2 of Jingxi Optics) to complete the collection of photon signals.

[0046] When the analog signal detection branch is selected, the optical path selection mechanism (such as splitting by a beam splitter 24 or adjusting the rotatable mirror 14 to another angle) guides the fluorescence and converges it to the light-sensitive surface of a photodetector (such as a photodetector with a model of PDA36A2 of Sorebo) by a plano-convex lens 27. An attenuation sheet can be provided in the optical path to avoid saturation of the detector. The photodetector converts the total fluorescence intensity into a continuous analog voltage signal. The signal output by this branch is suitable for measuring the continuous wave optical detection magnetic resonance (CW-ODMR) spectrum, and is combined with a lock-in amplifier to evaluate the sensing sensitivity of the system.

[0047] The electronic control and data acquisition module of the embodiment of the application serves as the control center of the integrated device, which integrates the signal generation and data acquisition functions required for the two measurement modes of pulsed quantum characterization and continuous wave sensing characterization.

[0048] In a specific embodiment, as Figure 5As shown, the electronic control and data acquisition module includes a microwave radio frequency driving box, a single photon detector (e.g., SPCM-AQRH-14-FC), a digital delay pulse signal generator (e.g., Guo Yi Quantum ASG8100), a microwave source (e.g., Puyuan Jingdian DSG836), a phase-locked amplifier, a gain-adjustable photoelectric detector (e.g., PDA36A of Thorlabs), and a computer for cooperative control. Among them, the phase-locked amplifier, the microwave source and the digital delay pulse signal generator are connected with the computer through USB lines and communicate and controlled by the system software control module.

[0049] The microwave-radio frequency driving box is internally integrated with: a microcontroller (e.g., STM32F103ZET6) as the control core of the box; a radio frequency source (e.g., ADF4351) for generating a 100MHz radio frequency signal for driving the acousto-optic modulator 8; a radio frequency attenuator chip (e.g., HMC624A); a band filter (e.g., BPF88-108MHz); two high-isolation switches (e.g., Mini-Circuits ZASWA-2-50DR+) respectively for controlling the on-off of the radio frequency and microwave signals; and two fixed-multiple power amplifiers for amplifying the radio frequency and microwave signals. The microcontroller communicates with the computer through a USB line in a serial protocol and configures the registers of the radio frequency source and the radio frequency attenuator chip through an SPI protocol to generate a radio frequency signal with a frequency of 100MHz, a power of -5dBm and an adjustable attenuation. The radio frequency signal is output after passing through the band filter, the high-isolation switch and the power amplifier (amplifying 30dBm) and is used to drive the acousto-optic modulator 8. The microwave signal output by the external microwave source can be introduced into the box, pass through another high-isolation switch and a power amplifier (amplifying 30dBm) and be output for manipulating the NV color center spin.

[0050] The electronic control and data acquisition module also includes a power module, the structure of which can refer to Figure 6 The power module is driven by a DC power adapter transformer receiving 220V mains power, generates multiple sets of stable DC voltages through a multi-channel switch DC step-down power supply (e.g., using LM2596 and LM2594 chips) and a positive and negative power conversion module (e.g., using dual TPS5430 chips), and respectively supplies power to the digital delay pulse signal generator (12V), the radio frequency source and the attenuator chip (5V), the high-isolation switch (±5V), the single photon detector (5V), the photoelectric detector (±12V) and the two power amplifiers (5V and 12V).

[0051] The electronic control and data acquisition module has two working modes to correspond to different measurement requirements.

[0052] In the first working mode, i.e., the pulse working mode, the connection of the electronic components is as shown in Figure 5The solid line shows. In this way, the digital delay pulse signal generator as a timing control core, generates at least two TTL pulse sequence, respectively control the microwave - radio frequency drive box in the radio frequency switch and the microwave switch, so as to realize the accurate timing control of laser pulse and microwave pulse. At the same time, the pulse generator in the preset time window to the TTL signal from the single photon detector counting. This way is used to perform Rabi oscillation, Ramsey interference, Hahn echo and spin relaxation experiment, in order to characterize the quantum properties of diamond NV color center.

[0053] In the second working mode, namely continuous / modulation working mode, the connection of electronic components is shown by the dashed line in the figure. Figure 5 The dashed line shows. In this way, the lock-in amplifier generates low frequency AC reference signal, which is sent to the microwave source, so as to modulate its output frequency or amplitude. At the same time, the photodetector converts the total fluorescence intensity collected into an analog voltage signal, and inputs it into the lock-in amplifier. The lock-in amplifier uses the internal reference signal to lock-in demodulate the input voltage, and extracts the weak fluorescence modulation signal from the high background noise. This way is used to obtain high signal-to-noise ratio of optical detection magnetic resonance spectrum, and further through the analysis of the noise spectrum of the demodulation signal, the sensing sensitivity of the system can be evaluated.

[0054] The system software control module of the embodiment of the application is the key to realize the automation and ease of use of the integrated device, which provides a unified operation platform, encapsulates the complex quantum measurement and sensing evaluation process into a standardized measurement task.

[0055] In a specific embodiment, the system software control module adopts a hierarchical control architecture. The architecture includes: bottom layer driver, host computer logic control program, and graphical user interface (GUI).

[0056] The bottom layer driver can be developed based on Keil5 integrated programming environment. It is responsible for receiving and executing the bottom layer hardware instructions from the host computer, such as communicating with the radio frequency source, digital attenuator and other chips through serial peripheral interface (SPI) protocol, and realizing the accurate control of radio frequency signal frequency and power by configuring the registers of these chips. At the same time, the program communicates with the host computer through universal synchronous / asynchronous receiver / transmitter (USART) protocol, and executes the commands sent by the host computer.

[0057] The host computer logic control program, for example, can be written in Python language, as the control core of the system, is responsible for realizing the logic flow of all experiments. The graphical user interface, for example, can be developed based on PyQt5 software package, provides a visual interactive interface for users.

[0058] The host computer logic control program can be written in Python language, as the control core of the system, responsible for implementing the logical flow of all experiments. The program realizes the coordinated control of all hardware modules in the system through various ways: it can communicate with the microcontroller in the microwave-rf drive box through the serial port protocol and the preset command system; it can control the digital delay pulse signal generator, lock-in amplifier and camera 15 through the software development kit (SDK) provided by the instrument manufacturer; and it can control the microwave source through the standard programmable instrument command (SCPI) protocol. The program is responsible for converting the experimental parameters set by the user on the GUI into precise hardware control sequences, thereby realizing the time synchronization scheduling of laser pulses, microwave pulses, data acquisition windows, etc.

[0059] The graphical user interface (GUI) can be developed based on the PyQt5 software package, providing a visual interactive interface for users. The core feature of the GUI is that it integrates two completely different measurement modes of quantum characteristic representation and sensing sensitivity evaluation in the same operation platform. Users do not need to write program codes, but only need to configure parameters on the interface to perform complete experiments and obtain analysis results.

[0060] In specific operation, the software module can perform the following functions: first, in the experiment preparation stage, the host computer program controls the camera 15 to perform continuous image acquisition and real-time display of fluorescence microscopic imaging, assisting the user to complete focusing by manually adjusting the sample displacement table 20, and moving the laser focus spot to a specific position of the diamond sample. Subsequently, the program displays the fluorescence photon counting value in real time through the single photon detector and the digital delay pulse signal generator, guiding the user to adjust the laser power or the attenuator so that the photon counting is within the linear working area of the single photon detector and the signal intensity is improved.

[0061] When the user selects to perform the quantum characteristic representation task, the GUI presents the corresponding parameter setting interface, and the user can input the parameters of the pulse sequence (such as Rabi oscillation, Ramsey interference, Hahn echo, spin relaxation, etc.) on it. After confirmation, the host computer logic control program will automatically generate the corresponding timing, accurately execute the pulse sequence through the control of the digital delay pulse signal generator, microwave source and microwave-rf drive box, and synchronously collect photon counting data, and finally real-time draw the measurement results on the interface.

[0062] When the user selects to perform the sensing sensitivity evaluation task, the GUI switches to another set of parameter setting interfaces, where the user can configure the sweep range, step frequency, parameters of the lock-in amplifier (such as time constant, modulation frequency), and the like of the continuous wave optical detection magnetic resonance (CW-ODMR). After confirmation, the host computer logic control program will coordinate the microwave source to perform frequency sweeping and frequency modulation, and collect the demodulated signal from the lock-in amplifier, and real-time draw the ODMR spectrum. Further, the software can also automatically perform noise spectral density analysis at the maximum slope of the spectrum, and calculate the final magnetic field sensing sensitivity.

[0063] Reference is made to the accompanying drawings Figure 7 Before performing the sensing experiment, the sample to be measured and the microwave radiator need to be assembled. In a specific sample preparation embodiment, first, the diamond sample to be measured is cleaned and fixed on a printed circuit board. For micron or nanometer diamond solution, it can be first dropped onto a clean glass slide, and after the solvent is evaporated, the glass slide is fixed on the printed circuit board. Subsequently, a copper wire with a diameter of about 18 μm is used as the microwave radiator, and its two ends are fixed on the solder pads of the printed circuit board through soldering and are pulled tight so as to tightly adhere to the surface of the diamond sample. The printed circuit board also integrates an SMA coaxial cable connector for receiving the microwave signal from the electronic control and data acquisition module. After assembly, the resistance of the copper wire at both ends can be measured using a multimeter to preliminarily confirm that the microwave line connection is normal.

[0064] The assembled sample together with the printed circuit board is fixed on the sample holder 19 in the inverted optical microscope module and is installed on the sample displacement stage 20. The sample displacement stage 20 can be a manual micron displacement stage (such as the LD60-RM-2 displacement stage of Ruijia pneumatic type), which is used to realize the precise positioning of the sample in three dimensions. At the same time, the external magnetic field application system provided by the module is composed of a magnet 16, a magnet holder 17, and a magnet displacement stage 18, which is used to apply a precise external bias magnetic field to the NV center.

[0065] In terms of the optical path, the optical fiber from the laser module is connected to the optical fiber coupling head 25 of the module. The outgoing excitation light is reflected by the high-pass dichroic mirror 23 and is guided by at least three cage system mirrors 22, and is finally focused on the sample surface by the objective lens 21.

[0066] The fluorescence generated by the NV center after excitation is collected by the same objective lens 21, propagates in the reverse direction of the excitation light path, and is transmitted after passing through the high-pass dichroic mirror 23 and the long-pass filter, and enters the multi-mode fluorescence detection optical path. Through optical path selection mechanisms such as the rotatable mirror 14, the fluorescence can be guided to the imaging detection branch, the confocal single-photon counting branch, or the analog signal detection branch, respectively.

[0067] After the whole system is built, the performance of the sample assembly needs to be verified. The host computer software controls the system to perform fluorescence imaging and continuous wave optical detection magnetic resonance (CW-ODMR) experiments. By optimizing the laser focus position, microwave power and other parameters, it is ensured that the contrast of the ODMR spectrum obtained is greater than 10%. When the contrast reaches this level, it is proved that the microwave radiator can effectively apply a microwave field to the target NV color center, ensuring that the subsequent quantum coherence characterization and sensing measurement experiments can be carried out smoothly. If the contrast cannot reach this level, the microwave radiator needs to be optimized, such as adjusting the contact between the copper wire and the sample surface or re-making the sample.

[0068] Reference is made to the accompanying drawings Figure 8 In order to illustrate how the integrated diamond quantum characterization and sensing device of the present application works, the specific operation process will be described in detail below through two representative measurement modes, quantum characterization and magnetic field sensing sensitivity evaluation.

[0069] When performing quantum characterization, the system mainly works in pulse mode, and the operation process is as follows: First, the experiment is prepared. According to the sample assembly method, the printed circuit board on which the diamond sample and the microwave copper wire are fixed is installed on the sample displacement table 20 of the inverted optical microscope module. The laser module is started through the graphical user interface (GUI) of the system software control module, and the camera 15 is controlled to perform real-time fluorescence imaging. The operator adjusts the sample displacement table 20 to make the sample surface image clear, and accurately positions the laser focus spot near the microwave copper wire (as shown in FIG. 1). Figure 8

[0070] Subsequently, the fluorescence detection light path is switched to the confocal single-photon counting branch through the GUI, and the output signal of the single-photon counter 13 is counted using the digital delay pulse signal generator in the electronic control and data acquisition module. The output power of the laser module is adjusted so that the photon count value reaches the optimal value in the linear region of the single-photon counter 13 (for example, close to 2Mcps). Finally, the microwave source and microwave switch are controlled by software to verify that the microwave radiator can effectively act on the sample.

[0071] After the preparation work is completed, a series of quantum characterization measurements can be performed. For example, by scanning and finding the fluorescence maximum value point in the sample, the ratio of the sample fluorescence to the standard sample fluorescence is used to estimate the NV color center concentration (as shown in FIG. 2). Figure 8

[0072] By performing continuous wave optical detection magnetic resonance (ODMR) scanning and adjusting the external magnet 16 to make the magnetic field along a certain NV axis, an ODMR spectrum with four resonance valleys can be obtained (as shown in FIG. 3). Figure 8 ​​(3) shown), so as to select a two-level quantum bit for subsequent coherent manipulation experiments.

[0073] Subsequently, the system software control module can automatically perform a series of pulse sequence experiments: by running the Rabi oscillation experiment program, the change of fluorescence contrast with microwave pulse length is measured, and the π / 2 and π pulse times are fitted (as shown in FIG. 8 Figure 8 (4) shown); the Ramsey interference experiment program is run, and the dephasing time T2* is measured and fitted (as shown in FIG. 8 Figure 8 (5) shown); the Hahn echo experiment program is run, and the dephasing time T2 is measured and fitted (as shown in FIG. 8 Figure 8 (6) shown); the spin relaxation experiment program is run, and the spin relaxation time T1 is measured and fitted (as shown in FIG. 8 Figure 8 (7) shown), the sensing sensitivity using the axial magnetic field is calculated according to the formula , the magnetic field detection sensitivity based on the Ramsey sequence is calculated according to the formula , and the alternating magnetic field detection sensitivity based on the Hahn echo sequence is calculated according to the formula When performing magnetic field sensing sensitivity evaluation, the system is switched to continuous / modulation operation mode, and the operation process is as follows: First, the experimental preparation is performed. By selecting the second working mode through the GUI, the software will automatically configure the electronic control and data acquisition module to enter the lock-in amplifier mode. The operator switches the fluorescence detection light path to the analog signal detection branch, so that the fluorescence signal is received by the photodetector. Through the virtual oscilloscope function on the GUI, the laser power and photodetector gain are adjusted to maximize the output voltage signal and prevent saturation.

[0074] After preparation, the formal measurement is started. The system software control module executes the preset Python program to cooperatively control the lock-in amplifier and the microwave source. The lock-in amplifier generates a low-frequency modulation signal to modulate the output frequency of the microwave source, while the center frequency of the microwave source is scanned within a preset range. The lock-in amplifier performs lock-in demodulation on the voltage signal output by the photodetector, thereby obtaining a high signal-to-noise ratio lock-in ODMR spectrum (as shown in FIG. 8 Figure 8 (8)). Subsequently, the software module automatically performs Lorentz fitting on the region with the largest slope in the spectrum to obtain the electron gyromagnetic ratio The voltage-to-magnetic field conversion coefficient is calculated. Then, the program fixes the microwave frequency at the point of maximum slope and controls the lock-in amplifier to collect data for a period of time (e.g. 1 second). For the collected 1-second lock-in time series signal, the power spectral density (PSD) is calculated using a Python program. The periodogram function is used to calculate a spectrum with frequency as the horizontal axis and power per unit Hertz (voltage squared per Hertz) as the vertical axis, which represents the noise power of different frequency components. Combined with the previously calculated conversion coefficient, the final magnetic field sensor sensitivity curve is obtained in units of T / √Hz (as shown in FIG. 9). Figure 8 (9) can also collect long-time signals to calculate their Allan variance to evaluate the stability of the system (as shown in FIG. 10). Figure 8

[0075] The above operation flow shows that the present application can conveniently and efficiently complete the comprehensive characterization of the quantum properties of diamond NV color centers and the accurate evaluation of the sensing performance through the organic combination of various modules. Based on the platform provided by the present application, through the functional expansion of the sample stage, such as the combination with a scanning galvanometer, a piezoelectric ceramic sheet, a diamond anvil cell or a low-temperature system, two-dimensional or three-dimensional imaging of physical quantities can be further realized, as well as quantum sensing under extreme conditions such as a wide temperature range and a wide pressure.​

Claims

1. An integrated device for characterizing the quantum properties and sensing sensitivity of nitrogen vacancy color centers, characterized in that, The device is mounted on an optical breadboard (2) and includes: Laser module: includes a laser (4), a power and polarization adjustment unit consisting of a half-wave plate (5) and a polarization beam splitter (6), an acousto-optic modulator (8), and an optical fiber coupler (10). The laser module is used to selectively guide the laser from the laser (4) to an optical path that bypasses or passes through the acousto-optic modulator (8) to generate a continuous laser beam or a pulsed laser beam. The inverted optical microscope module includes an optical fiber coupler (25), several cage-type system mirrors (22), a high-pass dichroic mirror (23), an objective lens (21), and an optical path selection mechanism. The optical fiber coupler (25) is used to receive the continuous laser beam or pulsed laser beam, which is reflected by the high-pass dichroic mirror (23) and focused by the objective lens (21) onto the sample fixed by the sample holder (19). The objective lens (21) collects the fluorescence generated by the sample, which is transmitted through the high-pass dichroic mirror (23) along the reverse optical path and then guided by the optical path selection mechanism to different detection branches. Electronic control and data acquisition module: used to provide drive signals to the active devices in the laser module and the inverted optical microscope module, and to receive and process signals from the single-photon counter (13) and the photodetector; System software control module: running on a computer, used to coordinate and control the aforementioned modules to execute the corresponding measurement process according to the quantum property characterization task or sensing sensitivity evaluation task selected by the user.

2. The integrated device for characterizing the quantum properties and sensing sensitivity of nitrogen vacancy color centers according to claim 1, characterized in that, When the laser module generates the pulsed laser beam, the electronic control and data acquisition module applies a radio frequency driving signal to the acousto-optic modulator (8) to cause the laser beam to diffract. The aperture (9) is configured to selectively allow the first-order diffracted beam to pass through the fiber coupler (10).

3. The integrated device for characterizing the quantum properties and sensing sensitivity of nitrogen vacancy color centers according to claim 1, characterized in that, When the laser module generates the continuous laser beam, it adjusts the plane mirror (7) in the optical path to make the laser beam bypass the acousto-optic modulator (8) and directly guide it to the fiber coupler (10).

4. The integrated device for characterizing the quantum properties and sensing sensitivity of nitrogen vacancy color centers according to claim 1, characterized in that, The optical path selection mechanism in the inverted optical microscope module includes at least one rotatable mirror (14) and a beam splitter (24). By placing or removing the rotatable mirror (14) into or out of the fluorescence path, fluorescence can be reflected to the camera (15) for imaging.

5. The integrated device for characterizing the quantum properties and sensing sensitivity of nitrogen vacancy color centers according to claim 4, characterized in that, When the rotatable mirror (14) is removed from the optical path, the fluorescence enters the confocal single-photon counting branch composed of the confocal collection system (26), which includes at least two plano-convex lenses (27) and a confocal aperture (12), and is finally detected by the single-photon counter (13).

6. The integrated device for characterizing the quantum properties and sensing sensitivity of nitrogen vacancy color centers according to claim 4, characterized in that, Through the optical path selection mechanism, the fluorescence is guided to the analog signal detection branch, which includes a plano-convex lens (27) and a photodetector. The photodetector converts the fluorescence intensity into an analog voltage signal and outputs it to the lock-in amplifier in the electronic control and data acquisition module.

7. The integrated device for characterizing the quantum properties and sensing sensitivity of nitrogen vacancy color centers according to claim 1, characterized in that, The inverted optical microscope module also includes a sample displacement stage (20) and an external magnetic field application system; the sample displacement stage (20) is used to carry and precisely position the sample; the external magnetic field application system includes a magnet (16), a magnet holder (17) and a magnet displacement stage (18), which are used to adjust the magnetic field applied to the sample.

8. The integrated device for characterizing the quantum properties and sensing sensitivity of nitrogen vacancy color centers according to claim 1, characterized in that, When performing the quantum property characterization task, the electronic control and data acquisition module includes a timing control core, which is used to generate a synchronized pulse sequence to control the on / off state of the acousto-optic modulator (8) and microwave radiation, and to gate the single-photon counter (13) for counting within a specific time window.

9. The integrated device for characterizing the quantum properties and sensing sensitivity of nitrogen vacancy color centers according to claim 1, characterized in that, When performing the sensor sensitivity evaluation task, the electronic control and data acquisition module includes a microwave source and a lock-in amplifier; the lock-in amplifier generates a reference signal of a fixed frequency and inputs it to the microwave source, which can frequency modulate the microwave signal; the lock-in amplifier uses the low-frequency modulated signal as a reference signal to demodulate the signal from the photodetector.

10. The integrated device for characterizing the quantum properties and sensing sensitivity of nitrogen vacancy color centers according to claim 1, characterized in that, The inverted optical microscope module is encapsulated in an optical microscope box (11), and the laser module is encapsulated in a laser control system box (3). Both the optical microscope box (11) and the laser control system box (3) are fixed on the optical breadboard (2). The top of the optical breadboard (2) is provided with multiple pillars (1) to provide support for the laser module and the inverted optical microscope module.

Images