This paper explores a method for generating optically mediated entanglement between Bose-Einstein condensates (BECs). Using a quantum nondemolition Hamiltonian with BECs placed in a Mach-Zehnder configuration, it is shown that entangled states can be induced by performing measurement on light. In particular, the effects of the entangled state in the presence of decoherence were analyzed. The behavior of the entangled state was found to be sensitive to the atom-light interaction time. The entangled state is relatively stable when the dimensionless interaction time $ \tau \lesssim \frac{1}{\sqrt{N}} $ and relatively fragile when the time is greater.
In this paper, the atomic structure, stability, electronic structure, and magnetism of two-dimensional transition metal phosphide MnTn+1 (M = V, Cr; T = P, As, and Sb) slices were systematically studied using the first-principles calculations based on density functional theory. By calculating the formation energy and phonon spectrum, it was determined that only V4As5, Cr2P3, Cr3P4, Cr4P5, Cr2As3, and Cr3As4 are stable two-dimensional magnetic multilayers. The results show that these stable two-dimensional magnetic materials are antiferromagnetic metals. In addition, the electronic structure and the magnetic coupling mechanism of these materials were further analyzed.
The (2 + 1)-dimensional Dirac oscillator is a fundamental model used to study the relativistic extensions of quantum effects and principles. Due to the influence of relativistic effects, including the non-equidistant and negative excitation spectrum and the spin-orbit coupling, the eigenstates are complicated dressed states composed of spin and angular momentum state vectors; in turn, this renders theoretical research difficult. In this work, we decouple the spin and angular momentum state vectors and separate the spin-up and -down components into positive- and negative-energy states, respectively, using the Foldy-Wouthuysen (F-W) transformation. The Hamiltonian and eigenstates of the Dirac oscillator are then largely simplified in the F-W representation; nevertheless, we find the forms of the operators for spin and angular momentum in the same representation with complex combinations of each other. The results are useful in advancing research in relativistic quantum mechanics and spin-orbit coupling.
Recently, research on multi-mode, multi-band transceivers has garnered significant interest; in this context, the Software-Define Radio (SDR) system is considered a good candidate. To reduce the negative influence of out-of-band interference on transceiver performance of the SDR system, a high out-of-band rejection IF (intermediate frequency) filter with tunable bandwidth and programable gain is proposed. The proposed filter consists of a biquadratic Gm-C filter, a gain-boosting stage, and a 5th-order elliptic filter. In the proposed filter, the variable gain is achieved using a biquadratic Gm-C filter and a gain-boosting stage, and the tunable bandwidth is achieved using capacitor arrays. In addition, a 5th-order elliptic filter is added to improve out-of-band rejection. The post-layout simulation shows that the bandwidth is tuned over a range of 1 MHz–30 MHz, and the minimum out-of-band rejection at twice the bandwidth reaches 44.56 dB. The gain control range is from –20 dB to 20 dB, and the power consumption and active area for the analog counterpart is 5.1 mW and 1.23 mm2, respectively. The proposed filter is suitable for the analog front-end of multi-mode communication terminals.
In this study, photoluminescence spectra are studied in perovskite quantum dot superlattices based on two-photon absorption processes at 10 K. The dynamics of excitons is obtained using a time-resolved photoluminescence detection system. The sample exhibits typical superfluorescence characteristics in the single-photon excitation case: When the pumping power increases, the transient peak intensity increases nonlinearly, and the radiation lifetime decreases rapidly. Meanwhile, the intensities of the two-photon absorption fluorescence spectra are proportional to the square of the excitation power, and the dynamics of excitons under the two-photon absorption case exhibits the same characteristics as those in the single-photon excitation case. Thus, when the excitation density reaches a certain intensity, two-photon absorption can also induce a superfluorescence process.
In this paper, the motion trajectory of micro-nanoparticles is calculated based on the Euler-Richardson algorithm after the optical force exerted on the particles is determined using Mie scattering theory. The Euler-Richardson algorithm has better calculation accuracy and faster convergence speed than the Euler algorithm and the Euler-Kromer algorithm, and thus is an appropriate approach to describe the trajectory of particles. Hence, the motion trajectory of a nanoparticle in a periodic conservative optical force field is calculated based on the Euler-Kromer algorithm; the results confirm consistency with the physical analysis, further verifying the effectiveness and stability of the approach. The calculation method shown in this paper provides a high-efficiency approach to study optical trapping, transport, sorting of colloidal particles, and biological macromolecules as well as the cooling of macroscopic particles in optical micro-manipulation.
In this paper, the phase estimation limits of an active-related Mach-Zehnder interferometer with three port inputs and two different input states was studied using quantum Fisher information and quantum Fisher information matrix theory. In the case of an arbitrary light field input to a single port, the effect of the input field fluctuation on the limit of phase estimation is eliminated by the theory of phase averaging and the quantum Fischer information matrix. In the case of a dual port input coherent state, the effect of the fluctuating light field on the estimation limit cannot be eliminated, and the phase estimation limit depends on the initial phase of the two input coherent states.
In this paper, corrections to the octet baryon masses based on the strange quark contribution are calculated using the SU(3) covariant chiral effective theory. We find that the items violating chiral power counting rules are local and can be subtracted by local counterterms which leads to extended minimal subtraction ${(\text{E}}\overline {{\text{MS}}})$ scheme. In addition to the chiral contribution, relativistic correction items are also retained, which is meaningful for accurately calculating the corrections to baryon masses and analytical extrapolation.
In this study, ultrafast spin dynamics on FM-AFM (ferromagnetism-antiferromagnetism) thin film were explored using pump-probe technology with circularly polarized and linear pump beams. Circularly polarized light generates an effective inducting magnetic field, which is called the inverse Faraday effect. The direction of the transient Kerr peak only depends on the angular momentum of photons. The amplitude of the Kerr peak depends on the thickness of the MnIr film. This may be attributed to the fact that the transient Kerr peak originates from the magnetization of paramagnetic electrons. This study may help further the understanding of spin dynamics in HD-AOS (Helicity-Dependent All Optical Switching).
In this paper, the exterior solution for a spherically symmetric black hole surrounded by plasma is studied in detail. After deriving the fundamental governing equations, the analytic solutions under two approximate conditions, ${g_{tt}}{g_{rr}} = - 1$ and $p = 0$ , are investigated. Comparing the two results with the accurate numerical solution, we find that the former approximation offers superior accuracy. This provides a basis for studying the quasinormal modes of perturbations as well as the shadow and ring when the black hole is surrounded by plasma.
In this paper, we present a new type of atom-light accelerometer (ALA) based on use of an atom-light hybrid interferometer. At present, all-optical accelerometers are the most commonly used and most stable accelerometers on the market, owing to their small size and high accuracy. However, due to measurement bandwidth limitations, their practical application range is limited. Hence, we designed a new type of accelerometer to address this challenge. The atom-light hybrid interferometer is first constructed in the atomic system through the stimulated Raman scattering (SRS) process, and the elastic mass of the accelerometer is formed by a mirror. When the mass is subjected to acceleration on the experimental platform, it will perceive the change in external displacement, thereby introducing the phase into the interferometer. Through the change of the interference fringe, the change of the external phase and the displacement can be determined; hence, the magnitude of the acceleration can be obtained. The primary advantage of the atom-light accelerometer is that the Stokes field generated by the SRS process is phase related to the atomic spin-wave, which ensures the stability of the device phase. Secondly, the adjustable bandwidth of the device increases its scope of application. Finally, theoretical calculations show that its measurement accuracy exceeds the standard quantum limit (SQL) under ideal conditions.
In this paper, bandgap tuning of C3N through the stacking pattern, layer number, and external electric field were investigated by employing first-principles density functional theory (DFT) calculations. Four stacking structures—namely AA-1, AA-2, AB-1, and AB-2—were investigated in our study; the calculation results showed that the AB-2 structure was the most energetically favorable. Accurate calculations of the bandgap by the HSE06 hybrid functional revealed a large bandgap difference between the C3N bilayers with AA and AB stacking; specifically, structures with AA stacking had much smaller bandgap than those with AB stacking. Moreover, we found that the bandgap of C3N decreases from 1.21 eV for a single layer to 0.69 eV for the AB-2 bulk structure. By applying a vertical electric field, the bandgap of a C3N bilayer, tri-layer, and four-layer with AB-2 stacking can be tuned to a nearly metallic state.
In recent years, a new laser cooling method—named bichromatic adiabatic cooling—has been developed; however, the method offers low cooling efficiency. In this paper, numerical optimization of the bichromatic adiabatic cooling process has been performed. It is shown that there is an optimal pulse time for the optical fields to achieve the highest cooling efficiency. Moreover, a comparison of the cooling efficiency with the Gaussian light pulse and square pulse shows that the cooling efficiency is insensitive to the pulse shape. Because this cooling method relies on adiabatic evolution of the light field-atom system, it is shown that it is better to slow the speed of the atomic beam to maintain the adiabatic condition. Finally, the effect of spontaneous emission on bichromatic adiabatic cooling is studied. The results show that use of a long pulse significantly reduces cooling efficiency.
Research on complex networks has given birth to models for understanding evolution dynamics and structure formation; their respective degree growth fluctuations, however, behave very differently. To test the validity of existing models, we carry out an empirical study on two real networks. The results show that both their fluctuation exponents decrease linearly with the observation interval, presenting an interval-dependent picture that has not been predicted by any of the existing models. By exploring the response of the fluctuation to shuffling data, we deduce the interval dependence from the reinforcement of the internal temporal correlation. These results reveal not only the limitations of the existing models, but the complex dynamics of the correlation itself, which is significant for further understanding the underlying mechanism of network evolution.
In this paper, a method for testing the Bell correlation between two spatially separated two-mode squeezed Bose-Einstein condensates (BECs) is proposed. Using the referenced method, violation of the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality can be observed. First, the method for producing the required physical states is introduced, and then the Bell correlation is tested by calculating the relevant factors using the normalized expected value of the particle number operator. It is shown that violation of the Bell inequality can be observed when $r \lesssim 0.49$ . One of biggest violations occurs, furthermore, when $r \to 0$ and $B = 2\sqrt 2 $ . The method is highly robust in the presence of noise.
This paper studies the use of quantum nondemolition (QND) measurement to produce a spin squeezed atomic Bose-Einstein condensate (BEC) in a double-well trap. The spin squeezed atomic Bose-Einstein condensate is performed by putting the BECs of a double well in the two arms of a Mach Zehnder interferometer and performing a QND measurement. The dynamics of the light-atom system are solved using an exact wave-function approach, in contrast to previous approaches where approximations were made using techniques like the Holstein-Primakoff approximation. The backaction of the measurement on atoms is minimized by monitoring the condensate at zero detection current and the identical coherent beams. At the weak atom-light interaction limit, we find that the average spin direction is relatively unaffected by observing the conditional probability distribution and the Q function distribution. The spin variance is squeezed along the axis of optical coupling.
In this study, we investigated the dynamic behavior of quantum Fisher information (QFI) for the qubit-qutrit system suffering from noisy environments by considering quantum memory; the qubit is located near the event horizon of the Garfinkle-Horowitz-Strominger (GHS) dilation black hole and the qutrit stays at the asymptotically flat region. We proposed an effective strategy to protect QFI under the influence of noise by employing weak measurement and reversal measurement. The results show that QFI decays as the amplitude damping strength increases; meanwhile, QFI is nearly constant with an increase in the phase damping strength. QFI can be improved with the selection of appropriate values for measurement strengths and reversal strengths.
In this study, the electronic structure and magnetism of the Heusler alloy Fe2CrGe are investigated using first-principle calculations. Results show that the ground state of Fe2CrGe is antiferromagnetic metal in which Fe ion and Cr ion are in low- and high-spin states of $ S=0 $ and $ S=1 $ , respectively. The energy of the antiferromagnetic state is approximately 0.103 eV less than that of the ferromagnetic state. In addition, when a tetragonal strain is applied to Fe2CrGe, a transition from antiferromagnetic to ferromagnetic material occurs at +1.7% and –1.7% strains, and Fe2CrGe becomes a ferromagnetic half-metal. A half-metal energy gap of approximately 0.2 eV occurs when the strain reaches ±5%. The Curie temperature of Fe2CrGe is estimated to be 393 K, which is much higher than room temperature, indicating that Fe2CrGe may be a potential candidate for spintronic applications.
The optical response characteristics of a subwavelength lithium niobate film guided-mode resonance metasurface were investigated via simulations. The influences of parameters such as the period, filling factor and etching depth of the etched micro–nano structure on the transmission spectrum were examined, and the effects of light sources with different polarization states and incidence angles on the spectral linewidth were imvestigated. Because of the asymmetric grating structure design, the bound states in the continuum (BIC) decay into a quasi-BIC mode with a high Q value (>10 000), and the second harmonic conversion efficiency of the subwavelength lithium niobate film increases by five orders of magnitude as a result of the local field enhancement effect of the bound state. The simulation results show that a high-efficiency conversion of the second harmonic can be realized in the ultraviolet band when the peak power density of the incident fundamental wave is on the order of ~1 GW/cm2, that is, the ultraviolet second harmonic conversion efficiency emitted after a single pass through the subwavelength lithium niobate film is up to 10–3 orders of magnitude. This study affords ideas and design schemes for improving the nonlinear response characteristics of a micro–nano structure and optical table interface system.
Temporal modes are a set of orthogonal wave-packet modes that can be used to characterize temporal multi-mode quantum light fields. They provide a complete alternate theoretical framework for the description of quantum systems. This study is based on light-induced seeding as an input to stimulated Raman scattering (SRS), whose output, the Stokes field, is the input seed field of the next SRS ; thus, the process of a continuous iterative SRS system is realized. The pump light field is then fixed in a Gaussian waveform and super-Gaussian waveform, and the temporal waveform evolution characteristics of the output Stokes light field under the input of Gaussian waveform seed light with various structures are studied. The seed light injection can obtain the same stable waveform output through iteration, and the FWHM (full-width at the half of the maximum) of the output light field waveform depends on the pump light field. Furthermore, Schmidt mode decomposition is applied to the final stable output waveform, and the eigenvalues of the final output Stokes field are all concentrated in the fundamental mode by numerical calculation. The research on the temporal mode properties of light presented in this paper provides theoretical guidance and experimental reference for the further development and utilization of the quantum resource of temporal modes.
中国综合性科技类核心期刊(北大核心)
