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GENERAL

Experimental study of efficient temporal-multimode Duan-Lukin-Cirac-Zoller storage scheme
Wen Ya-Fei, Zhuang Yuan-Yuan, Wang Zhi-Qiang, Gao Shi-Hui
2024, 73 (18): 180301. doi: 10.7498/aps.73.20240799
Abstract +
Quantum interfaces that generate entanglement or correlations between a photon and an atomic memory are fundamental building blocks in quantum repeater research. Temporal, spatial, and spectral multiplexed atom–photon entanglement interfaces in cold atomic systems based on spontaneous Raman scattering processes, present an effective technical approach to realizing quantum repeaters. Compared with the other schemes, temporal-multiplexing schemes are particularly attractive since they repeatedly use the same physical process. In these schemes, readout efficiency plays a crucial role. Theoretical models indicate that even if the readout efficiency is increased by 1%, the probability of long-distance entanglement distribution will be increased by 7%–18%. However, current implementation of temporal-multimode quantum memory often suffers low readout efficiency unless an optical cavity or an atomic ensemble with a large optical-depth is adopted.In this study, we solve this challenge by using the expandable pulsed light fabricating technology and carefully selecting energy level transitions, so as to develop an efficient temporal-multiplexed quantum source. Our approach involves applying a train of write laser pulses to an atomic ensemble from different directions, thereby creating spin-wave memories and Stokes-photon emissions. We design an expandable pulsed light fabrication device based on the principle of optical path reversibility, allowing a writing laser beam to pass through an acousto-optic modulator (AOM) network in two different directions. This setup enables precise control over the directions of the write pulse train through real-time manipulation of the field-programmable gate array (FPGA) and the diffraction order of the AOMs. In our experiment, we prepare six pairs of modes. After detecting Stokes photons during the experimental cycle, the FPGA outputs a feedforward signal after a specified storage time, triggering the application of a corresponding reading pulse from the read AOM network to the atomic ensemble, thereby generating an anti-Stokes photon. To enhance readout efficiency, we optimize the energy level structure of the read pulse transitions, $ \left| {{{b}} \to {{{e}}_2}} \right\rangle $ to $ \left| {{{b}} \to {{{e}}_1}} \right\rangle $; specifically, we adjust the transition frequencies of the read pulses by comparing with those used in current temporal-multimode quantum memory schemes. Theoretical calculations show that when the frequencies of the read pulses are tuned to the transitions $ \left| {{{b}} \to {{{e}}_1}} \right\rangle $ and $ \left| {{{b}} \to {{{e}}_2}} \right\rangle $, the readout efficiencies are about 33% and 15%, suggesting that the chosen energy level transitions can double the readout efficiency.Experimental results indicate a readout efficiency of 38% for the multiplexed source and the Bell parameter of 2.35. Additionally, our device has a 5.83-fold higher probability of successfully generating entanglement than a single channel entanglement source. Our method is cost-effective, easy to operate, and highly applicable. For instance, based on our findings, the readout efficiency can be further improved through cavity-enhanced atom–photon coupling, and entanglement fidelity can be increased by suppressing noise in temporal-multimode memory schemes. This work provides a solid foundation and effective methods for realizing the high-efficiency temporal-multimode quantum memory and developing the large-scale quantum networks.

GENERAL

Dynamic and scalable secret sharing schemes based on matrix product compressed states
Lai Hong, Wan Lin-Chun
2024, 73 (18): 180302. doi: 10.7498/aps.73.20240191
Abstract +
Currently, quantum secret sharing (QSS) schemes based on entangled states have not yet fully utilized the potential of the probability amplitude of entangled states. However, the probability amplitude is a key characteristic of quantum information science and possesses significant application prospects in the fields of quantum computing and quantum communication. It is worth noting that entangled states can be effectively represented by matrix product states (MPSs). The representation of entangled states using MPS can precisely reveal the entanglement characteristics closely related to the probability amplitude.This study first focuses on the representation of the W state by using MPS, an approach that allows us to determine the key conditions for W state to achieve quantum advantage in QSS. Subsequently, this research demonstrates that by representing entangled states with MPS, a W state can be compressed into a single photon state and a simplified matrix form, presenting an innovative technical path.Moreover, one of the most attractive features of our proposed QSS scheme is its ability to compress multiple different quantum states (represented by photons) into a unified state represented by a single photon. This characteristic endows our scheme with scalability and flexibility, meaning that the group of participants can be easily expanded or reduced according to their specific needs. The addition of new participants is managed by Alice, who is responsible for the distribution of quantum state shares. On the other hand, when a participant leaves the group, their old quantum state share can be simply ignored in the process of recovering the secret's quantum state, thereby simplifying the management process.Through this strategy, we can not only make effective use of entangled resources but also meet the various requirements of the system, including but not limited to communication security, data transfer rates, and system scalability. This research provides new perspectives and possibilities for the field of quantum information science and may have a significant influence on the development of the field.

GENERAL

Controllable multistability of fractional-order memristive Henon map and its application in video encryption
Zhang Hong-Wei, Fu Chang-Lei, Pan Zhi-Xiang, Ding Da-Wei, Wang Jin, Yang Zong-Li, Liu Tao
2024, 73 (18): 180501. doi: 10.7498/aps.73.20240942
Abstract +
In recent years, the use of discrete memristors to enhance chaotic maps has received increasing attention. The introduction of memristors increases the complexity of chaotic maps, making them suitable for engineering applications based on chaotic systems. In this work, a fractional-order discrete memristor exhibiting local activity and controllable asymptotic stability points is constructed by using multiband nonlinear functions. The locally active property of this memristor is demonstrated by using the power-off plot and DC v - i plot. It is then introduced into the Henon map to construct a fractional-order memristive Henon map that can generate any number of coexisting attractors. Simulation results show that the number of fixed points in the system is controlled by the memristor parameters and related to the number of coexisting attractors, thus achieving controllable homogeneous multistability. The complex dynamical behaviors of this map are analyzed by using phase portraits, bifurcation diagrams, maximum Lyapunov exponent (MLE), and attractor basins. Numerical simulations show that the fractional-order map can generate various periodic orbits, chaotic attractors, and period-doubling bifurcations. The system is then implemented on an ARM digital platform. The experimental results are consistent with the simulation results, confirming the accuracy of the theoretical analysis and its physical feasibility. Finally, a parallel video encryption algorithm is designed by using the chaotic sequence iteratively generated by fraction-order memory Henon mapping, which mainly includes frame pixel scrambling and diffusion. Comprehensive security analyses are conducted, proving the robustness and reliability of the proposed encryption scheme. The results show that the encryption algorithm can effectively protect video information. In the future, we will explore other methods of constructing chaotic or hyperchaotic systems with controllable multistability and study their circuit implementation, synchronization control, and chaos-based engineering applications.

GENERAL

Analysis of mixed rhythm and its dynamics in closed-loop respiratory control system driven by electromagnetic induction
Chen Xue-Li, Xia Lu-Yuan, Wang Zhi-Hui, Duan Li-Xia
2024, 73 (18): 180502. doi: 10.7498/aps.73.20240847
Abstract +
The pre-Bötzinger complex is a crucial region for generating respiratory rhythms in mammals. Peripheral chemoreceptors have a significant influence on respiratory rhythm by monitoring changes in blood oxygen concentration and carbon dioxide concentration. This study introduces a closed-loop respiratory control model, which is driven by electromagnetic induction and based on the activation of pre-Bötzinger complex neurons. The model incorporates various factors including the motor pool, lung volume, lung oxygen, blood oxygen, and chemoreceptors. The response of the system subjected to the same hypoxic perturbation under different electromagnetic induction is studied, and the control effect of magnetic flux feedback coefficient on the recovery of mixed rhythms is investigated. Using bifurcation analysis and numerical simulations, it is found that the magnetic flux feedback coefficient has a significant influence on the ability to recover respiratory rhythm. The dynamic mechanism of the magnetic flux feedback coefficient on different hypoxic responses in closed-loop systems are revealed. Dynamic analysis indicates that under certain electromagnetic induction, the mixed bursting rhythm in the closed-loop system can autoresuscitate if the bifurcation structure before and after applying hypoxia perturbation are completely identical. However, when the bifurcation structure before and after applying hypoxia perturbation are different, the mixed bursting rhythm in the system cannot autoresuscitate. In addition, for the cases where automatic recovery is not achieved under mild electromagnetic induction, increasing the magnetic flux feedback coefficient appropriately can lead the system to autoresuscitate, which is closely related to the Hopf bifurcation and fold bifurcation of limit cycle. This study contributes to understanding the influence of the interaction between the central respiratory and peripheral chemoreceptive feedback on respiratory rhythm, as well as the control effect of external induction on the hypoxic response.

GENERAL

Finite and fixed-time synchronization of memristive chaotic systems based on sliding mode reaching law
Lai Qiang, Wang Jun
2024, 73 (18): 180503. doi: 10.7498/aps.73.20241013
Abstract +
Two innovative sliding mode control laws based on the convergence principle of reaching law are presented in this work. These control laws are used to achieve both finite-time and fixed-time synchronization for a specific class of memristive chaotic system, which are known for their intricate and complex dynamical behaviors. By utilizing these control strategies, we can effectively manage the synchronization process and ensure rapid convergence. Firstly, for the finite-time synchronization issue, a novel power reaching law is derived. Compared with the conventional reaching law, the reaching law presented in this work has a prominent advantage that the chattering of the sliding mode control is reduced to a lesser extent and the speed of reaching the sliding surface is quicker. An upper bound of the stabilization time, which is dependent on the initial conditions of the system, is obtained and the system is proved stable. For the fixed time synchronization problem, a new double power reaching law is put forward to minimize the chattering and accelerate the convergence. Then, by utilizing the fixed time stability theory, the upper bound of the convergence time that remains invariant with the initial value of the system is derived. Finally, in order to verify the effectiveness and feasibility of the theoretical derivation in this paper, two sets of control experiments are set up and the influences of the two control laws on the system synchronization state are compared. The experimental phenomenon strongly proves the accuracy of the proposed theorem.

GENERAL

Research and application of differential optical absorption two-dimensional detection system for rotorcraft unmanned aerial vehicle
Ye Fan, Li Su-Wen, Mou Fu-Sheng, Wang Song, Wang Zhi-Duo, Tang Yu-Jie, Luo Jing
2024, 73 (18): 180701. doi: 10.7498/aps.73.20240909
Abstract +
In order to meet the technical requirements for miniaturization, multi-angle, multi-altitude, and fast simultaneous acquisition of atmospheric pollutants, this study develops an integrated, lightweight, and cost-effective airborne differential optical absorption spectroscopy (DOAS) system. This system is designed in order to be used on a rotorcraft unmanned aerial vehicle (UAV) platform for monitoring atmospheric pollutants. The compositions of the hexacopter UAV platform and the airborne DOAS system are detailed in this work. The system includes a multi axis differential optical absorption spectroscopy (MAX-DOAS) spectral acquisition system, a control system, and a flight environment monitoring system. Commands are sent from a computer via serial communication to drive a gimbal, controlling the azimuth angle and elevation angle of the telescope, with a camera recording the light obstruction. The sunlight scattered by the atmosphere is collected by the telescope and transmitted via fiber optics to the spectrometer, which then transmits the data to the control computer. Additionally, the system captures data of altitude, temperature, humidity, and GPS location during flight, and filters out spectral data obtained under abnormal flight conditions. Stability studies indicate that the mean angular deviations for yaw, roll, and pitch are 0.07°, –0.13°, and –0.12° respectively, which meet the requirements for monitoring stability. Comparative experiments with a commercial ground-based DOAS system show that the correlation coefficients between the monitoring data of both systems are both greater than 0.92, confirming the reliability of the airborne system. In field flight experiments, the airborne DOAS system conducts observations at altitudes of 30 m, 60 m, and 90 m, with the elevation angle set at 0° and the azimuth angle measured every 30° from 0° to 360°. The system successfully obtains the concentration distributions of NO2, SO2, and HCHO at different azimuth angles and altitudes. The results indicate that the concentrations of these three gases decrease with altitude increasing, with higher concentrations observed in the southeast direction, indicating the presence of pollution sources in that direction. Further analysis with considering altitude changes indicates that the rate of decrease in NO2 concentration and SO2 concentration slow down with altitude increasing, while the rate of decrease in HCHO remains relatively constant. These findings indicate that this system effectively meets the technical requirements for simultaneous, rapid, multi-angle, and multi-altitude detection of atmospheric pollutants, providing essential support for the detailed monitoring of complex urban micro-environments.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Dual-band semi-Dirac cones in two-dimensional photonic crystal and zero-index material
Ji Yu-Xuan, Zhang Ming-Kai, Li Yan
2024, 73 (18): 181101. doi: 10.7498/aps.73.20240800
Abstract +
Semi-Dirac cones, a type of unique dispersion relation, always exhibit a series of interesting transport properties, such as electromagnetic topological transitions and anisotropic electromagnetic transmission. Recently, dual-band semi-Dirac cones have been found in three-dimensional photonic crystals, presenting great potential in electromagnetic wave regulation. However, to the best of our knowledge, there has been no report on dual-band semi-Dirac cones and their applications in two-dimensional photonic crystals, and most of two-dimensional systems have only realized semi-Dirac cones at a single frequency. Therefore, we are to realize dual-band semi-Dirac cones in two-dimensional photonic crystals.In this work, a type of two-dimensional photonic crystal that comprises a square lattice of elliptical cylinders embedded in air is proposed. By rotating the elliptical cylinders and adjusting their sizes appropriately, accidental degeneracy at two different frequencies is achieved simultaneously in the center of the Brillouin zone. Using ${\boldsymbol{k}} \cdot {\boldsymbol{p}}$ perturbation theory, the dispersion relations near the two degenerate points are proved to be nonlinear in one direction, and linear in other directions. These results indicate that the double accidental degenerate points are two semi-Dirac points with different frequencies, and two different semi-Dirac cones, i.e. dual-band semi-Dirac cones, are realized simultaneously in our designed photonic crystal. More interestingly, the dual-band semi-Dirac cones exhibit opposite linear and nonlinear dispersion relation along the major axis and the minor axis of the ellipse, respectively. And our photonic crystal can be equivalent to an impedance-matched double-zero index material in the direction of linear dispersion and a single-zero index material in the direction of nonlinear dispersion, which is demonstrated by the perfect transmission in the straight waveguide and wavefront shaping capabilities of electromagnetic waves. Based on the different properties of the equivalent zero-refractive-indices near the frequencies of two semi-Dirac point, the designed Y-type waveguide can be used to realize frequency separation by leading out the plane waves of different frequencies along different ports. We believe that our work is meaningful in broadening the exploration of the band structures of two-dimensional photonic crystals and providing greater convenience for regulating electromagnetic waves.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Midrapidity average transverse momentum of identified charged particles in high-energy heavy-ion collisions
Xie Zhen, Li Jing-Xing, Zheng Hua, Zhang Wen-Chao, Zhu Li-Lin, Liu Xing-Quan, Tan Zhi-Guang, Zhou Dai-Mei, Bonasera Aldo
2024, 73 (18): 181201. doi: 10.7498/aps.73.20240905
Abstract +
The average transverse momentum $\left\langle p_{\mathrm{T}} \right\rangle$ of final particles is an important observable in high-energy heavy-ion collision experiments. It reflects the properties of soft hadrons and thermonuclear matter, and it can also be used to deduce the information about the evolution of collision systems. By using the phenomenological linear and power-law functions, we study the dependence of the average transverse momentum $\langle p_{\mathrm{T}}\rangle$ at midrapidity in Au + Au and Pb + Pb collisions from the STAR, PHENIX and ALICE Collaborations on four normalized physical quantities, i.e. the collision centrality, the average number of binary collisions per participant pair $\dfrac{2N_{{\mathrm{coll}}}}{N_{{\mathrm{part}}}}$, the average pseudorapidity density of charged particles per participant pair $\dfrac{2}{N_{{\mathrm{part}}}}\dfrac{{\mathrm{d}}N_{{\mathrm{ch}}}}{{\mathrm{d}}\eta}$ and the average pseudorapidity density of charged particles per binary collision $\dfrac{1}{N_{{\mathrm{coll}}}}\dfrac{{\mathrm{d}}N_{{\mathrm{ch}}}}{{\mathrm{d}}\eta} $. The results show that the average transverse momentum $\langle p_{\mathrm{T}} \rangle$ of identified particles exhibits a good linear relationship with collision centrality, and it follows a nice power-law relationship with the average number of binary collisions per participant pair $\dfrac{2N_{{\mathrm{coll}}}}{N_{{\mathrm{part}}}}$, the average pseudorapidity density of charged particles per participant pair $\dfrac{2}{N_{{\mathrm{part}}}}\dfrac{{\mathrm{d}}N_{{\mathrm{ch}}}}{{\mathrm{d}}\eta}$, and the average pseudorapidity density of charged particles per binary collision $\dfrac{1}{N_{{\mathrm{coll}}}}\dfrac{{\mathrm{d}}N_{{\mathrm{ch}}}}{{\mathrm{d}}\eta}$. It is also found that the fitting parameters in the proposed phenomenological functions for the average transverse momentum $\langle p_{\mathrm{T}} \rangle$ with collision centrality and the average number of binary collisions per participant pair follow a power-law function with collision energy, which endows the phenomenological approach with predictive ability. Therefore, the collision centrality and the average number of binary collisions per participant pair are good physical quantities for studying the average transverse momentum of identified particles in high-energy heavy-ion collisions. The results in this study can be used to predict the average transverse momentum of identified particles at other collision energy of which the experimental data are not available so far. The mass ordering of the average transverse momentum of identified particles, i.e. $\text{π}^{-},\;{\mathrm{K}}^{-} $ and $\bar{{\mathrm{p}}}$, is also discussed and explained by the particle production time related to energy conservation, at a given collision centrality and energy.

ATOMIC AND MOLECULAR PHYSICS

First-principles calculations of point defect migration mechanisms in InP
Yan Li-Bin, Bai Yu-Rong, Li Pei, Liu Wen-Bo, He Huan, He Chao-Hui, Zhao Xiao-Hong
2024, 73 (18): 183101. doi: 10.7498/aps.73.20240754
Abstract +
As an important second-generation semiconductor material, indium phosphide (InP) possesses excellent advantages such as a wide bandgap, high electron mobility, high photoelectric conversion efficiency, and strong radiation resistance. It is considered an excellent material for electronic devices in aerospace applications. However, point defects generated by space radiation particles in InP electronic devices can cause their electrical performance to degrade severely. In this study, first-principles calculations are employed to investigate the stable structures of point defects in InP and calculate the migration energy values of nearest-neighbor defects. Four stable structures of In vacancies and three stable structures of P vacancies are identified by constructing the stable structures of point defects in different charge states. The migration process of vacancy defects is studied, revealing that the migration energy of P vacancies is higher than that of In vacancies. Moreover, charged vacancy defects exhibit higher migration energy values than neutral vacancies. Regarding the migration process of interstitial defects, it is found that the migration energy of interstitial defects is smaller than that of vacancy defects. In the calculation of In interstitial migration process with different charge states, two different migration processes are found. Besides, during the migration calculations of P interstitial, a special intermediate state is discovered, resulting in multiple paths migrating to the nearest-neighbor position in the migration energy barrier diagram. The research results are helpful to understand the formation mechanism and migration behavior of defects in InP materials, and are important in designing and manufacturing InP devices with long-term stable operation in space environment.

ATOMIC AND MOLECULAR PHYSICS

Effects of different compositional ratios on physical structure and optical properties of thin films during alloying of Zn2+ and TiO2
Xiao Wen-Yue, Dong Xiao-Shuo, Mamatrishat Mamat, Niu Na-Na, Li Guo-Dong, Zhu Ze-Tao, Bi Jie-Hao
2024, 73 (18): 183301. doi: 10.7498/aps.73.20240814
Abstract +
A batch of TiO2 films with different Zn2+ compositions are prepared on a single crystal silicon substrate by using sol-gel method to observe the changes in optical and photocatalytic properties in the alloying process of Zn2+ and TiO2. X-ray diffractometer (XRD) is used to observe the changes in the crystal structures of the films in the alloying process and to track the formation of ZnTiO3 compounds. Scanning electron microscope (SEM) and atomic force microscope (AFM) are used to observe the phenomena of a large number of holes on the surfaces of the films due to the limited solubility of the crystal lattice for Zn2+ in the alloying process. X-ray photoelectron spectroscopy (XPS) and optical bandgap are used to observe the changes at a level of the electronic structure of the films in the alloying process of Zn2+ with TiO2. Finally, by degrading the methylene blue solution, it is shown that a small amount of Zn2+ doping is completely dissolved in TiO2, destroying the TiO2 crystalline quality. As the compositional share of Zn2+ continues to increase to 15%, the limited solubility of TiO2 for Zn2+ is verified in the XPS peak fitting, resulting in a large number of hole structures in the film, and the active specific surface area of the film is enhanced, while Zn2+ effectively traps the photogenerated e–/h+. In order to continue to observe the effect of Zn2+ concentration on TiO2, we increase the concentration of Zn2+ to 40% and observe the phenomenon in the alloying process of Zn2+ with TiO2. It is shown that the appearance of the compound ZnTiO3 can act as a complex center for e–/h+ and a significant decrease in the percentage of TiO2 leads to a gradual decrease in the photocatalytic efficiency of the films after alloying.
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