Since the orbital angular momentum entangled state can theoretically constitute an infinite-dimensional quantum entangled state, the research on the quantum non-local correlation testing based on it is of great significance to verify the correctness of the quantum mechanics theory. However, during the experimental preparation of quantum states, the orbital angular momentum entangled state prepared is usually a mixed state due to the influence of environmental noise. Starting, starting from the description of the quantum non-local correlation test logic based on Hardy’s theorem and applicable to the orbital angular momentum mixed state, this paper attempts to test its possibility of the first and second order stepnumbers of the Werner-like orbital angular momentum mixed state quantum Non-local association. Theoretical analysis shows that in the first-order and second-order cases, when the degree of mixing satisfies Tr(ρ2)>0.786 and Tr(ρ2)>0.651 respectively, the orbital angular momentum mixed state can be successfully tested for quantum non-local correlation. In addition, the research results of this article also show that the use of Hardy’s theorem with two ladder can significantly increase the range of successful quantum non-local correlation tests compared with one ladder.

In this paper, we systematically investigated the geometric quantum discord of Heisenberg spin chain models in a Non-Markovian environment using a Non-Markovian quantum state diffusion method proposed by Diosi and Gisin in 1998. Geometrical quantum discord was used to describe quantum correlations as proposed by Dakic et al. In the first place the reduced density matrix of the system was calculated by the Non-Markovian quantum state diffusion master equation. Afterward, the reduced density matrix was brought into the quantum discord formula, thus achieving a numerical precise simulation of the geometric quantum discord of the Heisenberg spin chain. At length the evolution of the geometric quantum discord of Heisenberg spin chain models with various parameters vs time was discussed in this paper, using the maximally entangled state |ψAB〉=12|11〉+00e as the initial state of Heisenberg spin chain model of the system. According to the numerical simulation results, the environmental correlation coefficient γ, parameters J, parameters a and parameters η can all influence the evolution of the system geometric quantum discord dynamics to different degrees. When the environmental correlation coefficient γ is very small, the geometric quantum discord shows a significant upward trend, showing that non-Markovian environmentsplay a positive role on the geometric quantum discord of the system. Also large parameters J, a and η also play a positive role on the geometric quantum discord of the system. The present study has a certain role and significance for increasing the geometric quantum discord of the system, providing a theoretical basis for the experimental researchers in practice.

The cavity increases the rotation angle by increasing the length of the interaction between probe light and atoms, which greatly improves the sensitivity of a magnetometer. On an atomic magnetometer based on the non-linear magneto-optical effect, we have theoretically and experimentally studied the relationship between the enhancement factor of the sensitivity and the reflectivity of the cavity mirror, and obtained the optimal sensitivity with certain loss of probe light in atomic vapor cell. In a plano-concave standing-wave cavity, when the reflectivity of the input mirror and output coupling mirror is respectively 99.5% and 88%, the loss of the light intensity of the atomic vapor cell is 9.5% and 8.5sdown,thesensitivityofthemagnetometerisimproved,andthecavityenhancementeffectismoresignificant.

High-precision parameter estimation plays an important role in modern science and technology. Quantum weak measurement is a technique that can be used to amplify and estimate small parameters. It is of great significance to explore the influence of quantum weak measurement on the precision of parameter estimation. The weak measurement process mainly involves two physical systems: the system and the pointer. This process consists of three main steps: first, preparing the initial state of the system and the pointer; second, the system weakly interacts with the pointer; third, the system is postselected to a final state that is nearly orthogonal to its initial state. Many factors affect the estimation precision of the coupling parameters. In this paper, the influence of the initial state parameters of the pointer (mean and variance of coordinate distribution), coupling constant and post-selection angle on the estimation precision of the coupling parameters are investigated when the spatial degree of freedom and polarized degree of freedom of the beam are coupled through a birefringent crystal. We specifically discuss the influence of relevant parameters on the Fisher information of coupling parameters to be estimated, and analyze the influence on the estimation precision of coupling parameters. The results show that (1) increasing the variance and the mean value (the center position) of the initial state coordinate distribution can improve the post-selection probability and increase the total Fisher information; (2) The smaller the coupling constant, the higher the estimation precision, but the lower the corresponding post-selection probability; (3) Under the condition of weak measurement approximation, the more orthogonal the post-selection state and the initial state of the system are, the higher the estimation precision is. Therefore, we can obtain larger Fisher information about the parameters to be estimated by appropriately adjusting these tunable parameters, that is, to improve the estimation precision of the coupling parameters.

High accuracy optical clock is regarded as an important tool for testing general relativity, relativistic geodesy and dark matter detection. So far ytterbium optical clock shows the best stability, which reaches 10－19 level after averaging 36 h. Control unit is the vital part of the ytterbium optical clock. It mainly takes on time sequence generation for the clock system. In this paper, a field programmable gate array (FPGA) control unit based on Python language is introduced to ytterbium optical clock. On one hand, it can generate various control signal for ytterbium optical clock by compiling and calling the subroutine. On the other hand, it can be used for data storage and processing during the clock operation. The results show that data processing with the FPGA system can be perfectly matched with traditional method dealt with Matlab and Origin program, and cold atoms with micro Kelvin level and clock transition spectra with Hertz level are obtained in ytterbium clock system. More importantly, based on the noise analysis database in earlier experiment, fitting to the complex clock transition spectra with multi-Gaussian superimposition function can act as a method for machine learning, which is a better way for experimental process analysis and fault diagnose. It would benefit for gravitational wave detection and hunting for dark matter with more accurate atomic optical clock based on machine learning in the future.

Spatial optical soliton is the result of the balance between diffraction and nonlinear effect when light propagates in nonlinear media. The soliton pair can overlap and interact when two beams of incoherent lightpropagate in a nonlinear medium. The propagation characteristics and interaction of incoherently coupled dark soliton pairs in self-defocusing media were studied. By using the variational method, the parameter evolution equations of two dark solitons propagating in self-defocusing Kerr media were obtained based on the coupled nonlinear Schrdinger equations which describe beam propagation. First, the parameter evolution equations of two dark solitons propagating in self-defocusing Kerr media were obtained, and the evolution rules of soliton parameters were discussed. Then, in order to analyze the interaction between solitons, the function of the distance between two dark solitons with equal amplitude was derived, and the soliton pair transmission image and interaction image were given. Finally, the expressions of interaction potential energy and interaction force between solitons were derived, and the interaction characteristics between solitons were analyzed in detail by using images. The results show that the amplitude of the solitons is not affected by the coupling effect in the case of no loss and remains unchanged in the transmission process. The coupling interaction makes the coordinates of the two solitons shift obviously. When the distance between the two solitons is small, the distance between the two solitons varies with the transmission distance, and the change rate is related to the amplitude and coupling coefficient of the solitons. When the distance between the two solitons approaches zero, the distance between the two solitons changes steadily with the transmission distance. The interaction force between dark solitons is repulsive. With the decrease of the distance between solitons, the repulsive force first increases and then decreases, but the interaction potential energy gradually decreases. When the distance between solitons increases to about 4.5, the potential energy between dark solitons decreases to almost zero.

Based on the nonlinear Schrdinger equation with nonlocal nonlinear effects, we studied the propagation dynamics of the finite-energy Airy beams with initial chirp in competing nonlocal nonlinear media by using the split-step Fourier method. The results show that the initial chirp can change the propagation velocity of the single finite-energy Airy beam, and the larger the chirp, the greater the pulse offset velocity. However, the chirp has little effect on the breathing period and amplitude of the beam. When the initial input is double Airy beams, the chirp increases the repulsive force between the two beams in the weak nonlocal medium, thus affecting the breathing period of the solions. In the strong nonlocal medium, the interaction between the two beams is more complex, showing a quasi-periodic characteristic with complex structure, but the chirp leads to the periodic change of the quasi-periodic structure; with the increase of the absolute value of the chirp, the period of the quasi-periodic structure becomes larger, and the beam diffraction is enhanced.

In order to improve the sensitivity of the temperature sensor, this sensor based on a microfiber interference and nanomaterial (boron nitride (BN) dispersion) encapsulation has been proposed in this study. The microfiber interference has a simple fabrication process, which was manufactured by using a butane flame brushing for tapering a commercial multimode fiber to micron scale. The smaller the diameter of the microfiber is, the stronger the evanescent field is.The interaction between the evanescent potential field and the external environment was enhanced. It was a trade-off between sensitivity and stability of microfiber interference, with the selected diameter of 12.3?m in the experiments. This microfiber interference was encapsulated in a capillary tube including BN dispersion with high thermo-optical coefficient to form this senor. In order to prevent liquid leakage, both ends of the capillary tube were sealed with the ultraviolet (UV) glues. The microfiber interference spectrum was stable after sealing with UV glue. The refractive index of the BN dispersion was more sensitive to temperature changes, which results in wavelength shift of microfiber interference. Therefore, the temperature response of this senor encapsulated with BN is measured by observing the drift of the transmission spectrum. The results show that the blueshifts of the wavelength occurs with the temperature increases, and the sensitivity of the temperature sensor encapsulated with BN can up to －0.2878?nm/°C, which is more than 10 times higher than without BN encapsulation (the sensitivity of －0.0297?nm/°C). The concentration of BN dispersion has little effect on the temperature sensitivity. The sensor has the advantages of small structure, light weight, low cost, and high mechanical properties. Moreover, the encapsulation can protect the microfiber interference from sensing deformation caused by environmental changes and contamination of thesensing part by external impurities, which can improve the accuracy of the experiment. This sensor has great application potential in the field of temperature sensing.

In this paper, the high-order quantum correlation effect is investigated in an asymmetric semiconductor quantum well with a three-level cascade-configuration structure, in which three dipole-allowed transitions are simultaneously driven by three laser fields. We find that the intensity-intensity correlation and intensity-amplitude correlation are strongly dependent on the relative phase and the Rabi frequencies of the driving fields. We assume that all of the Rabi frequencies for the three driven fields are identical. When the relative phase is 0, the intensity-intensity correlation shows strong correlation; otherwise, the normal correlations are obtained. On the other hand, the intensity-amplitude correlations are also modified by the relative phase. When the collective phase is taken as π/2 or 3π/2, the correlation functions in positive time region and negative time region is approximately symmetrical with each other. In addition, we also find that theintensity-intensity and intensity-amplitude correlations are strongly modified by the Rabi frequencies. When the collective phase is zero, the intensity-intensity correlation can be changed from strong correlation into normal correlation by modifying theRabi frequency; not only that, the values of third-order correlation can also be greatly enhanced during this process. In order to analyze the internal physics behind the above-mentioned phenomena, we use dressed-state transformation to calculate the decay rates in dressed-state picture. It is explored that there exits two closed decay channels between these dressed states, which lead to the occurrence of multiple quantum interference effects being responsible for the generation of the nonclassical higher-order correlation effects. Also, the dressed-state population is obtained at steady state. The result demonstrates that the quantum interference effects give rise to the coherent population trapping. When the atoms are trapped into the excited state, the anticorrelation is generated. In the other situation, the emitted resonance fluorescence photons show strong correlation when the atoms stay at the ground states. Importantly, the higher-order correlation effect in the semiconductor quantum well may be useful for the high-precision measurement and the detection of single-photon. It also may pave a way to explore the quantum properties of resonance fluorescence.

We experimentally demonstrated a frequency locking method for Rydberg transition laser without modulation by using electromagnetically induced transparency (EIT) spectroscopy in room temperature Rb vapor cell. The cascade three-level system of Rb atom consisted of ［EQUATION］, ［EQUATION］, and ［EQUATION］, where the probe laser excited the atoms in ground state ［EQUATION］to intermediate state ［EQUATION］and the coupling laser was usedto drive the atoms transition from intermediate state ［EQUATION］to Rydberg state ［EQUATION］. In the experiment, the probe laser was locked by saturated absorption spectroscopy (SAS). The EIT signal was monitored by scanning the frequency ofthe coupling laser and measuring the intensity of the probe laser. The probe laser frequency was modulated and the error signal was obtained by demodulating the EIT spectrum. In order to achieve the frequency locking of coupling laser, we feedbacked the error signal to the laser via the PID control circuit. Finally, a modulation-free frequency locking of the coupling laser is realized. Comparing with the traditional method where both two lasers need modulating, here only one laser need modulating. In this case, the frequency perturbation caused by modulation signal is suppressed and the long-term stability of frequency locking system can be improved. Thus, we realized the laser frequency locking without modulation and measured the frequency jitter after locking with the result about 1 MHz. The Allan variance was used to analyze the error signal. The Allan variance reached the minimum value in about 1 minute with the value of about ［EQUATION］when coupling laser was locked.

Quantum microwave has both the quantum characteristics of the quantum signal and the ability of long-distance propagation in free space. It has extensive applications in various fields, such as communication, radar, navigation and positioning. This article summarized and analyzed the characteristics of quantum microwave and its receiving methods in light of the relatively less research on the reception of quantum microwave at present. We started from introducing the characteristics and preparation methods of single microwave photon, entangled microwave photon pairs, and squeezed state or entangled state microwave fields. We then introduced the receiving principle and detection methods of quantum microwave, and particularly paid intensive attention on the current status and existing problems in both the quantum radar and other physical systems. The main problems include: the signal strength is rather weak at the receiver; the detection technique for the microwave entangled state is not mature enough; and the optimal detection operator is to be further optimized, etc. For this, we summarized and analyzed the potential strategies of lowering down the noise in the receiver to improve the signal to noise ratio, and the path entanglement microwave detection approach based on the entanglement witness. Thus, a closed path is completed starting from the preparation and generation until the receiving of the quantum microwave. We hope that this review can provide some support for the development of quantum systems on the microwave transmitting and receiving technology.