Bell non-locality and quantum coherence are two fascinating properties of quantum systems. They are not only of fundamental importance, but also crucial resources in quantum information processing. Bell non-locality refers to the quantum correlation that violates Bell inequality and cannot be explained by any local hidden variable model. Meanwhile, the violation of Bell inequality can also be used to indicate the existence of entanglement. Quantum coherence, arising from the quantum state superposition, marks the violation of quantum mechanics from the classical world, and is recognized as the foundation of quantum correlation. Due to the unwanted interaction between a quantum system and the environment, Bell non-locality and quantum coherence can be degraded. Thus, in order to utilize them better, much effort has been devoted to investigating the dynamics of Bell non-locality and quantum coherence in the open quantum systems with the single-layered environment. However, in fact, the quantum system can be affected by the hierarchical environment too, which is receiving increasing attention at present. Under this background, we explore in this paper the dynamics of Bell non-locality and quantum coherence of two identical qubits, each of them is coupled independently to its own hierarchical environment. The effects of coupling strength κ between the qubit and cavity, and the detuning δ between the frequency of cavity and the center frequency of reservoir on the dynamics of Bell non-locality and quantum coherence have been discussed in detail for the weak and strong coupling regimes. It has been shown that there exists the sudden death phenomenon of Bell non-locality in both coupling regimes. Meanwhile, the survival time or the value of Bell non-locality changes with κ and δ. In contrast, quantum coherence presents collapsing, revival, and other behaviors, and the peak value of revival will increase with the increase of κ and δ. Moreover, the effective manipulation of quantum weak measurement and measurement reversal operation on Bell non-locality and quantum coherence is investigated further. Several significant results are gained.

Gravitational waves propagate outward in the form of gravitational radiation. Their interaction with matter is minimal, but they are enough to cause a tiny phase difference of free mass. Ground gravitational wavedetectors are all based on Michelson interferometer. Laser-interferometer gravitational wave detectors are cavity-enhanced Michelson interferometers. Its five-length degree of freedom of the control system is an essential part of the whole interferometer. Measurement of locking matrix and coupling of degrees of freedom help to improve the control system. Laser interferometer for detecting gravitational radiation senses and measures the phase difference of laser through two arms of Michelson interferometer. This phase difference is generated when two beams recombine at the beam splitter, and is converted into observable intensity change through interference. For a given phase difference, the signal response is proportional to the optical power in the interferometer. The final sensitivity of the gravitational wave detector is determined by the signal response and background noise. Theoretically, the detection sensitivity can be improved by increasing the laser power. The signal size can be increased by increasing the total power of the light in the interferometer arm, so we adopted the method of power cycle to improve the sensitivity and measure the frequency response of the interferometer. In the experiment, the interferometer needs continuous monitoring and feedback to keep various parameters at the correct working point. In this paper, we found that the frequency response was enhanced by a factor of 6.15 by adding the power recovery mirror. Considering the loss of the system, this was consistent with the theoretical expectation. The degree of influence between locking signals can be measured by the locking matrix. In our experiment, the common-mode degree of freedom has little influence on the differential-mode error signal, but the differential-mode degree of freedom has a great influence on the common-mode error signal, which may be caused by the feedback of only one arm, which will be improved in the next experiment.

As a significant carrier of quantum information, the studies of qubits are providing more opportunities in emerging research fields such as quantum computation, quantum simulation and quantum metrology. However, due to the existence of a noise environment, such as magnetic signal fluctuation, the resulted decoherence of qubits limits its capabilities in the above-mentioned fields. Acknowledging the noise information can help us to break the limitation and improvethe applications of qubits, based on which crucial optimization of the customized dynamical decoupling protocols and suppression of the noise could be well realized. Thus, an accurate and efficient approach for analyzing the spectral information of the noise environment is required. Because of the difficulty of function inverse solution, conventional analytical methods based on approximation techniques can not accurately resolve the noise spectra from the interrogation-time-domain measurements of qubits.Recently, significant advance has been made in deep learning, which has been widely used for quantum information processing. In this paper, we propose a deep-learning-based method for noise spectral analysis of qubits. This method only needs to input thedecoherence curves into the deep-learning model to predict the existed environmental noise spectra. Through a series of iterative studies, this method can extract the potential mapping relation between the decoherence curves of qubits and corresponding noise spectra. We numerically simulate the deep-learning-based analysis process and demonstrate the good performance of our method. Moreover, benefited from the deep-learning-based algorithm, compared with the conventional method, the accuracy and efficiency of our method are much better. Our method also provides a new technique for other noise spectral analysis tasks and could be easily applied to a wide range of quantum systems.

We report to obtain dual-species Bose-Einstein condensates (BECs) of 39K-87Rb mixture in the hyperfine ground states F=1,mF=-1. Since the background scattering length of 39K is negative, we must manipulate the scattering length by Feshbach resonance to realize forced evaporative cooling of 39K. We measure the homonuclear and heteronuclear Feshbach resonance and determine the scattering strength in their hyperfine ground states |1,-1? at magnetic fields between 0 and 200 G. Two broad s-wave Feshbach resonances at 32.6 G and 162.8 G in the |1,-1? state induce the positive intraspecies scattering length of 39K in the region between them. Within this window, the interspecies scattering length of 39K-87Rb can be tuned by an s-wave Feshbach resonance at 117.6 G. We further compare the different magnetic field regions for the efficiency of evaporation cooling of 39K-87Rb mixture by optimizing the intraspecies and interspecies interactions. At last, we obtain the maximum dual-species BECs in the |1,-1? state at 117.8 G with the background repulsive interspecies scattering length aK～11a0 and the intraspecies scattering aRbK～286a0. This platform provides the opportunity to study quantum droplets.

In this paper, a simplified time-of-flight fluorescence imaging method is introduced for measuring the effective temperature of cold atom sample. The cooling laser for laser cooling and trapping atoms instead of the additional probe laser of standard time-of-flight fluorescence imaging. Based on the magneto-optical trap of cesium atom, the effective temperature of cold atoms is effectively reduced by using the technique of polarization gradient cooling. The effective temperature measurement of cesium atomic MOT (molasses) by means of simplified time-of-flight fluorescence imaging, with typical values are TY≈22.3±2.2K and TZ≈15.4±2.7K (TY≈11.6±1.1K and TZ≈2.8±1.2K). The simplified time-of-flight fluorescence imaging scheme proposed in this paper is easier to execution and promotion in experiments, without sacrificing the precision and accuracy of effective temperature measurement of the cold atom sample. It has positive significance and good promotion value for the application of cold atom microwave atomic clock, cold atom optical frequency atomic clock, cold atom gravimeter and other quantum precision measurement fields, as well as the further development of quantum optics and quantum information processing by using cold atom sample.

Based on the Peregrine soliton, the generation and evolution characteristics of breathing pulse in Erbium-doped fiber ring cavity are numerically studied in this paper. Peregrine soliton is a single high-peak pulse which is localized in both time and space. However, due to the interaction between the background wave and the soliton, Peregrine soliton splits into multiple sub-pulses in a single-mode fiber. In order to generate high-peak pulses for long-distance transmission, the background wave needs to be eliminated. In this paper, the Erbium-doped fiber ring cavity is used to eliminate the effect of background wave. The Erbium-doped fiber ring cavity is composed of single-mode fiber, Erbium-doped fiber and opticcouplers. By controlling the lengths of the single-mode fiber and the Erbium-doped fiber in the ring, the intra-cavity dispersion can reach nearly zero dispersion, and the dispersion management can be realized. The results show that the peak intensity ofbreathing pulse is related to the initial input of the Peregrine soliton. In order to obtain a high-intensity breathing pulse, the pulse of PS at the maximum excitation position is selected as the initial input of the fiber ring cavity. Under the action of the fiber ring cavity, the high-peak breathing pulses can be obtained and transmitted for a long distance in the Erbium-doped fiber ring cavity when the intracavity dispersion is near zero dispersion. And the background waves on both sides of the PS gradually evolve into small side lobes. The transmission characteristics of high peak breathing pulses are related to dispersion, nonlinear effects and small signal gain. High-peak breathing pulses can be generated when the net cavity dispersion is in the range ［-0.001?0,0.003?7］ps2. As the nonlinear coefficient increases, the peak intensity of breathing pulses increases, and the amplitude and frequency of oscillation increase. When the nonlinear coefficient increases to a certain extent, the local breathing pulse is gradually formed. With the increase of the small signal gain, the peak intensity of breathing pulses increases, but the amplitude and frequency of oscillation have a little change.

In order to realize the effective detection of volatile organic compounds in a narrow environment, a fiber-optic volatile organic compound sensor based on the probe structure is proposed in this paper. The sensoris connected by a single-mode fiber and a hollow-core fiber with a length of about 130m. The hollow-core fiber is embedded with a polydimethylsiloxane film with a thickness of about 15m. The size of the final sensor is only rm150m. Single-mode fiber, hollow-core fiber and polydimethylsiloxane film together constitute a Fabry-Perot cavity interferometer. When the polydimethylsiloxane film absorbs volatile organic compounds, it will cause its own volume expansion, which will change the Fabry-Perot cavity length and cause the interference wavelength to shift. The experimental results show that: First, the sensitivity of the proposed optical fiber volatile organic compound sensor based on the probe structure is 2.0 pm/ppm in the measurement range of 0～9 000 ppm isopropanol concentration, and when the minimum resolution of the spectrometer is 0.02 nm, the sensor has a detection limit of 10 ppm for volatile organic. Secondly, the sensor also showed good stability and repeatability. In the 30-minute stability test experiment, the actual measurement error range of the sensor was ±30 ppm, indicating good stability. Three repeatability experiments also verified that the sensor has good repeatability. Finally, the response time of the sensor is less than 42 s, indicating that it has a faster response speed. Overall, the sensor has high sensitivity and low detection limit in the detection of volatile organic compounds, good stability and repeatability, and fast response speed. Moreover, the manufacturing cost of the sensor itself is low, the production process is simple, and large-scale manufacturing can be realized. When measuring, the sensor is not limited by the space environment and can detect volatile organic compounds in a narrow environment.

The central spin inevitably interacts with the surrounding nuclear spin, resulting in decoherence, which has long been one of the severe challenges in quantum information and quantum computing. In this work, we have made some progress in this area. We propose a structure that preserves the coherence of the central spin perfectly for a long time, which consists of a spin-1/2 central spin coupled by XXZ hyperfine interaction to a spin chain interacting nonuniformly. When the central spin is in a superposition state, the bath spin is in an antiferromagnetic state as the initial state, and the coupling in the bath is strong, the central spin can approximately maintain the original coherence, and the hyperfine coupling in the xy direction is further removed, which can perfectly maintain the coherence. Using the central spin as a qubit, this structure can be applied to quantum computing, and it may realize lossless quantum computing. We use the bath spin to simulate the environment, apply the equation of motion method based on the analytical representation of the spin operator matrix element in the XX chain, and systematically study the effect of the environment on the decoherence dynamics of the central spin, focusing on the dynamics characteristics of the central spin decoherence factors under the influence of the non-uniform coupling between bath spins. In the process of controlling the non-uniform coupling between the bath spins from the minimum to the maximum, the coherent dynamics of the central spin roughly present six stages, showing rich quantum dynamic properties, and providing future research on the central spin dynamics as two important reference marks: the extreme value of the long-time mean value of thecoherence factor can be used as a sign to distinguish different phases; the equilibrium of the long-time evolution of the coherence factors can be used as a sign of the equivalence or multiple relationships between the coupling relations in the competitive equilibrium.

Ultra-stable lasers have become useful tools in frequency metrology and precision physics experiments such as optical clocks, optical frequency synthesizer, optical microwave generation, gravitational wave detection, and tests of fundamental physics. In these applications, lasers are required to have ultra-narrow linewidth and ultra-high short-term stabilization. To this aim, a laser is usually servo-locked to a high-finesse Fabry-Perot cavity by Pound-Drever-Hall (PDH) method. Thus the frequency stability of the laser is determined by the length stability of the cavity itself. Environmental vibrations especially due to low frequency (below 100 Hz) seismic and acoustic accelerations are one of those dominant noise sources, which result in quasi-static deformations of the cavity and then degrade the stability of the optical length between two mirrors. Ingenious and elaborate designing both in cavity spacer structure itself and its supports are necessary to decrease its vibration sensitivity. Here we report a tetrahedron-like optical reference cavity design that is insensitive to vibrations in all direction and to constrained force on the four support vertices of a tetrahedron. The ideal optimal cavity structure isobtained by truncating the cubic vertices to make the cavity length insensitive to the pressuring force. In the finite element analysis, the deformation due to low-frequency noise can be considered as the static case where a gravity-like force is appliedto the cavity. Thus the method can give quantitatively the acceleration sensitivity of the ultra-stable optical reference cavity. The calculated acceleration sensitivities for an ideal version of the mounted cavity are 0.1×10-11/g, 1.8×10-11/g, and 1.8×10-11/g (where g=9.81m/s-2) in the optical axis and two transverse directions. The high-fold symmetry of the cavity itself and the structural support can well constrain the rotation and translation freedom of the ultra-stable optical reference cavity, which makes it extremely insensitive to vibrations. The cavity design of low passive acceleration sensitivity combined with a rigid mount allows frequency stable lasers to operate in non-laboratory environments and will be an attractive candidate for transportable optical clock and space applications.

With the discovery of graphene, a frenzy was set in motion to explore two-dimensional materials and its potential applications. In recent years, considerable efforts have been devoted to the demonstration of atomically-thin optical devices using graphene, transition metal dichalcogenides, and other two-dimensional(2D) materials. The combination of two-dimensional materials and flat-optics has yielded fruitful unexpected results. These ultra-thin two-dimensional optical devices can not only realize the functions of traditional diffractive lenses, but also show excellent optical modulability in the sub-wavelength range, which broadens the potential of future applications. In addition to the excellent physical properties (such as good ductility and flexible substrate compatibility) of 2D materials, their Fermi level can be further tuned by gate voltage, thus effectively modulating the optical properties without moving the optical components, which makes the 2D ultra-thin optical components superior in terms of tunability as compared to conventional devices. Besides, tunable liquid crystal lens has a mature development, and graphene oxide, transition metal disulfide and many other two-dimensional materials also possess stable liquid crystal phases. It is natual to pay attention to ultrathin liquid crystal lenses based on two-dimensional materials in order to achieve the flexible and responsive two-dimensional tunable lenses. The emergence of two-dimensional ultra-thin tunable optics has not only paved the development of the next generation of optics, but also provided new hope for further high integration of optical components. Therefore, this review focuses on ultrathin lenses made of two-dimensional materials, as it will briefly outline the recent progress of subwavelength optical lenses made of two-dimensional layered materials as well as two-dimensional liquid crystal 2D materials. Moreover, this review also introduces the potential application of such lenses, and gives an outlook of this emerging research field.