Design of compact integrated diamond nitrogen-vacancy center quantum probe

An integrated quantum probe for magnetic field imaging is proposed,where the nitrogen–vacancy(NV)center fixed at the fiber tip is located on the periphery of flexible ring resonator.Using flexible polyimide(PI)as the substrate medium,we design a circular microstrip antenna,which can achieve a bandwidth of 140 MHz at Zeeman splitting frequency of 2.87 GHz,specifically suitable for NV center experiments.Subsequently,this antenna is seamlessly fixed at a three-dimensional-printed cylindrical support,allowing the optical fiber tip to extend out of a dedicated aperture.To mitigate errors originating from processing,precise tuning within a narrow range can be achieved by adjusting the conformal amplitude.Finally,we image the microwave magnetic field around the integrated probe with high resolution,and determine the suitable area for placing the fiber tip(SAP).

Current sensor based on diamond nitrogen-vacancy color center

High precision current measurement is very important for the calibration of various high-precision equipment and the measurement of other precision detection fields.A new current sensor based on diamond nitrogen-vacancy(NV)color center magnetic measurement method is proposed to realize the accurate measurement of current.This new current method can greatly improve the accuracy of current measurement.Experiments show that the linearity of the current sensor based on diamond NV color center can reach up to 33 ppm,which is superior to other current sensors and solves the problem of low linearity.When the range of input current is 5-40 A,the absolute error of the calculated current is less than 51μA,and the relative error is 2.42×10^(-6) at 40 A.Combined with the research content and results of the experiment,the application of the current sensor in the field of current precision measurement is prospected.

Orientation determination of nitrogen-vacancy center in diamond using a static magnetic field

Nitrogen-vacancy(NV)centers in a bulk diamond are often employed to realize measurement of multiple physical quantities,which depends on orientation information of NV axis.We report a fast and effective method to determine the orientation of NV axis with the aid of a static magnetic field.By measuring the optically detected magnetic resonance spectra,we can precisely extract the polar angle information between the NV axis and the known magnetic field.Combining with the polar angle information of different kinds of NV centers,we employ the Nelder-Mead algorithm to get the optimal solution of the orientation of NV axis.This method is simple and efficient,and is easily applied in NV-based quantum sensing.

Non-destructive Testing Method for Crack Based on Diamond Nitrogen-vacancy Color Center

Magnetic field measurement plays an extremely important role in material science,electronic en-gineering,power system and even industrial fields.In particular,magnetic field measurement provides a safe and reliable tool for industrial non-destructive testing.The sensitivity of magnetic field measurement deter-mines the highest level of detection.The diamond nitrogen-vacancy(NV)color center is a new type of quan-tum sensor developed in recent years.The external magnetic field will cause Zeeman splitting of the ground state energy level of the diamond NV color center.Optical detection magnetic resonance(ODMR),using a mi-crowave source and a lock-in amplifier to detect the resonant frequency of the NV color center,and finally the change of the resonant frequency can accurately calculate the size of the external magnetic field and the sensi-tivity of the external magnetic field change.In the experiment,a diamond containing a high concentration of NV color centers is coupled with an optical fiber to realize the preparation of a magnetic field scanning probe.Then,the surface cracks of the magnetized iron plate weld are scanned,and the scanning results are drawn into a two-dimensional magnetic force distribution map,according to the magnetic field gradient change of the magnetic force distribution map,the position and size of the crack can be judged very accurately,which pro-vides a very effective diagnostic tool for industrial safety.

Electron Spin Decoherence of Nitrogen-Vacancy Center Coupled to Multiple Spin Baths

We present the experimental results of nitrogen-vacancy （NV） electron spin decoherence, which are linked to the coexistence of electron spin bath of nitrogen impurity （PI center） and 13C nuclear spin bath. In previous works, only one dominant decoherence source is studied： P1 electron spin bath for type-Ⅰb diamond; or 13C nuclear spin bath for type-Ⅱa diamond. In general, the thermal fluctuation from both spin baths can be eliminated by the Hahn echo sequence, resulting in a long coherence time （T2 ） of about 400#8. However, in a high-purity type-Ⅱa diamond where 1℃ nuclear spin bath is the dominant decoherence source, dramatic decreases of NV electron spin T2 time caused by P1 electron spin bath are observed under certain magnetic field. We further apply the engineered Hahn echo sequence to confirm the decoherenee mechanism of multiple spin baths and quantitatively estimate the contribution of P1 electron spin bath. Our results are helpful to understand the NV decoherence mechanisms, which will benefit quantum computing and quantum metrology.

Scalable Quantum Information Transfer between Individual Nitrogen-Vacancy Centers by a Hybrid Quantum Interface

We develop a design of a hybrid quantum interface for quantum information transfer （QIT）, adopting a nanome- chanical resonator as the intermedium, which is magnetically coupled with individual nitrogen-vacancy centers as the solid qubits, while eapacitively coupled with a coplanar waveguide resonator as the quantum data bus. We describe the Hamiltonian of the model, and analytically demonstrate the QIT for both the resonant interaction and large detuning cases. The hybrid quantum interface allows for QIT between arbitrarily selected individual nitrogen-vacancy centers, and has advantages of the sealability and controllability. Our methods open an alter- native perspective for implementing QIT, which is important during quantum storing or processing procedures in quantum computing.

Time-bin-encoding-based remote states generation of nitrogen-vacancy centers through noisy channels

We design proposals to generate a remote Greenberger-Horne-Zeilinger（GHZ） state and a W state of nitrogenvacancy（NV） centers coupled to microtoroidal resonators（MTRs） through noisy channels by utilizing time-bin encoding processes and fast-optical-switch-based polarization rotation operations.The polarization and phase noise induced by noisy channels generally affect the time of state generation but not its success probability and fidelity.Besides,the above proposals can be generalized to n-qubit between two or among n remote nodes with success probability unity under ideal conditions.Furthennore,the proposals are robust for regular noise-changeable channels for the n-node case.This method is also useful in other remote quantum information processing tasks through noisy channels.

A Bright Single-Photon Source from Nitrogen-Vacancy Centers in Diamond Nanowires

Single-photon flux is one of the crucial properties of nitrogen vacancy （NV） centers in diamond for its application in quantum information techniques. Here we fabricate diamond conical nanowires to enhance the single-photon count rate. Through the interaction between tightly confined optical mode in nanowires and NV centers, the single-photon lifetime is much shortened and the collection efficiency is enhanced. As a result, the detected single-photon rate can be at 564 kcps, and the total detection coefficient can be 0.8%, which is much higher than that in bulk diamond. Such a nanowire single-photon device with high photon flux can be applied to improve the fidelity of quantum computation and the precision of quantum sensors.

Time-optimal control for hybrid systems based on the nitrogen-vacancy center

Fast and high fidelity quantum control is the key technology of quantum computing. The hybrid system composed of the nitrogen-vacancy center and nearby Carbon-13 nuclear spin is expected to solve this problem. The nitrogen-vacancy center electron spin enables fast operations for its strong coupling to the control field, whereas the nuclear spins preserve the coherence for their weak coupling to the environment. In this paper, we describe a strategy to achieve time-optimal control of the Carbon-13 nuclear spin qubit by alternating controlling the nitrogen-vacancy center electron spin as an actuator. We transform the qubit gate operation into a switched system. By using the maximum principle, we study the minimum time control of the switched system and obtain the time-optimal control of the qubit gate operation. We show that the X gate and Y gate operations are within 10μs while the fidelity reaches 0.995.

Preparation of Macroscopic Entangled Coherent States in Nitrogen-Vacancy Centers Ensembles Coupled to a Superconducting Flux Qubit

We propose a potentially practical scheme for creating macroscopic entangled coherent state between two separate nitrogen-vacancy center spin ensembles placed near a superconducting flux qubit. Through the collective magnetic coupling and the in situ tunability of the flux qubit, the arbitrary entangled coherent states of spin ensembles can be achieved with high success possibilities under the influence from decoherence of the flux qubit and spin ensembles.The experimental feasibility and challenge are justified using currently available technology.

Nonadiabatic holonomic quantum computation based on nitrogen-vacancy centers

Because of quantum superposition,quantum computation can solve many problems,such as factoring large integers[1]and searching unsorted databases[2,3],much faster than classical computation.To realize practical quantum computation and then gain the desired advantages,a universal set of quantum gates with sufficiently high fidelities are needed.However,various inevitable errors reduce the gate fidelities and finally collapse the computation results,which makes the realizations of quantum computation very challenging.To

High-resolution imaging of magnetic fields of banknote anti-counterfeiting strip using fiber diamond probe

Counterfeiting of modern banknotes poses a significant challenge,prompting the use of various preventive measures.One such measure is the magnetic anti-counterfeiting strip.However,due to its inherent weak magnetic properties,visualizing its magnetic distribution has been a longstanding challenge.In this work,we introduce an innovative method by using a fiber optic diamond probe,a highly sensitive quantum sensor designed specifically for detecting extremely weak magnetic fields.We employ this probe to achieve high-resolution imaging of the magnetic fields associated with the RMB 50denomination anti-counterfeiting strip.Additionally,we conduct computer simulations by using COMSOL Multiphysics software to deduce the potential geometric characteristics and material composition of the magnetic region within the anti-counterfeiting strip.The findings and method presented in this study hold broader significance,extending the RMB 50 denomination to various denominations of the Chinese currency and other items that employ magnetic anti-counterfeiting strips.These advances have the potential to significantly improve and promote security measures in order to prevent the banknotes from being counterfeited.

Design and simulation of an accelerometer based on NV center spin–strain coupling

The nitrogen-vacancy (NV) center quantum systems have emerged as versatile tools in the field of precision measurement because of their high sensitivity in spin state detection and miniaturization potential as solid-state platforms.In this paper,an acceleration sensing scheme based on NV spin–strain coupling is proposed,which can effectively eliminate the influence of the stray noise field introduced by traditional mechanical schemes.Through the finite element simulation,it is found that the measurement bandwidth of this ensemble NV spin system ranges from 3 kHz to hundreds of kHz with structure√optimization.The required power is at the sub-μW level,corresponding to a noise-limited sensitivity of 6.7×10^(-5) /√Hz.Compared with other types of accelerometers,this micro-sized diamond sensor proposed here has low power consumption,exquisite sensitivity,and integration potential.This research opens a fresh perspective to realize an accelerometer with appealing comprehensive performance applied in biomechanics and inertial measurement fields.

A spin-based magnetic scanning microscope for in-situ strain tuning of soft matter

We present a magnetic scanning microscope equipped with a nitrogen-vacancy(NV) center scanning probe that has the ability to mechanically tune the strain of soft matter in-situ. The construction of the microscope and a continuous straintuning sample holder are discussed. An optically detected magnetic resonance protocol utilized in the imaging is described.In order to show the reliability of this microscope, the strain conduction is estimated with finite element simulation, and xray diffraction is required for calibration when freestanding crystal films are under consideration. A magnetic imaging result is displayed to demonstrate the nano-scale imaging capability. The microscope presented in this work is helpful in studying strain-coupled magnetic physics such as magnetic phase transition under strain and strain-tuned cycloidal orientation tilting.

Magnetic field analysis in a diamond anvil cell for Meissner effect measurement by using the diamond NV^- center

Diamond negatively charged nitrogen-vacancy(NV-) centers provide an opportunity for the measurement of the Meissner effect on extremely small samples in a diamond anvil cell(DAC) due to their high sensitivity in detecting the tiny change of magnetic field. We report on the variation of magnetic field distribution in a DAC as a sample transforms from normal to superconducting state by using finite element analysis. The results show that the magnetic flux density has the largest change on the sidewall of the sample, where NV-centers can detect the strongest signal variation of the magnetic field. In addition, we study the effect of magnetic coil placement on the magnetic field variation. It is found that the optimal position for the coil to generate the greatest change in magnetic field strength is at the place as close to the sample as possible.

Nuclear spin induced collapse and revival shape of Rabi oscillations of a single electron spin in diamond

A collapse and revival shape of Rabi oscillations in an electron spin of a single nitrogen-vacancy centre has been observed in diamond at room temperature. Because of hyperfine interaction between the host ^14N nuclear spin and the nitrogen-vacancy centre electron spin, different orientations of the ^14N nuclear spins lead to a triplet splitting of the transition between ground state （ms = 0） and excited state （ms=1）. The manipulation of the single electron spin of nitrogen-vacancy centre is achieved by using a combination of selective microwave excitation and optical pumping at 532 nm. Microwaves can excite three transitions equally to induce three independent nutations and the shape of Rabi oscillations is a combination of the three nutations.

Single-channel vector magnetic information detection method based on diamond NV color center

A method of detecting the single channel triaxial magnetic field information based on diamond nitrogen-vacancy(NV)color center is introduced.Firstly,the incident angle of the bias magnetic field which can achieve the equal frequency difference optically-detected magnetic resonance(ODMR)spectrum of diamond NV color center is calculated theoretically,and the triaxial magnetic information solution model is also constructed.Secondly,the microwave time-controlled circuit module is designed to generate equal timing and equal frequency difference microwave pulse signals in one channel.Combining with the optical detection magnetic resonance technology,the purpose of sequentially locking and detecting the four formant signals on one side of the diamond NV color center(m_(s)=-1 state signal)is achieved,and the vector magnetic field information detection is accomplished by combining the triaxial magnetic information solution model.The system can obtain magnetic field detection in a range of 0 mT-0.82 mT.The system's magnetic noise sensitivity is 14.2 nT/Hz^(1/2),and the deviation angle errors of magnetic field detectionθ_(x) andθ_(y) are 1.3° and 8.2° respectively.

Dependence of nitrogen vacancy color centers on nitrogen concentration in synthetic diamond

Crystallization of diamond with different nitrogen concentrations was carried out with a FeNiCo-C system at pressure of 6.5 GPa.As the nitrogen concentration in diamond increased,the color of the synthesized diamond crystals changed from colorless to yellow and finally to atrovirens(a dark green).All the Raman peaks for the obtained crystals were located at about 1330 cm^(-1)and contained only the sp^(3)hybrid diamond phase.Based on Fourier transform infrared results,the nitrogen concentration of the colorless diamond was<1 ppm and absorption peaks corresponding to nitrogen impurities were not detected.However,the C-center nitrogen concentration of the atrovirens diamond reached 1030 ppm and the value of A-center nitrogen was approximately 180 ppm with a characteristic absorption peak at 1282 cm^(-1).Furthermore,neither the NV^(0)nor the NV^(-)optical color center existed in diamond crystal with nitrogen impurities of less than 1 ppm by photoluminescence measurement.However,Ni-related centers located at 695 nm and 793.6 nm were observed in colorless diamond.The NE8 color center at 793.6 nm has more potential for application than the common NV centers.NV^(0)and NV^(-)optical color centers coexist in diamond without any additives in the synthesis system.Importantly,only the NV^(-)color center was noticed in diamond with a higher nitrogen concentration,which maximized optimization of the NV^(-)/NV^(0)ratio in the diamond structure.This study has provided a new way to prepare diamond containing only NV^(-)optical color centers.

Quantum information processing with nitrogen–vacancy centers in diamond

Nitrogen-vacancy （NV） center in diamond is one of the most promising candidates to implement room temperature quantum computing. In this review, we briefly discuss the working principles and recent experimental progresses of this spin qubit. These results focus on understanding and prolonging center spin coherence, steering and probing spin states with dedicated quantum control techniques, and exploiting the quantum nature of these multi-spin systems, such as superposition and entanglement, to demonstrate the superiority of quantum information processing. Those techniques also stimulate the fast development of NV-based quantum sensing, which is an interdisciplinary field with great potential applications.

Implementation of a nonlocal N-qubit conditional phase gate using the nitrogen–vacancy center and microtoroidal resonator coupled systems

Implementation of a nonlocal multi-qubit conditional phase gate is an essential requirement in some quantum infor- mation processing （QIP） tasks. Recently, a novel solid-state cavity quantum electrodynamics （QED） system, in which the nitrogen-vacancy （NV） center in diamond is coupled to a microtoroidal resonator （MTR）, has been proposed as a poten- tial system for hybrid quantum information and computing. By virtue of such systems, we present a scheme to realize a nonlocal N-qubit conditional phase gate directly. Our scheme employs a cavity input-output process and single-photon interference, without the use of any auxiliary entanglement pair or classical communication. Considering the currently available technologies, our scheme might be quite useful among different nodes in quantum networks for large-scaled QIP.