Science China Physics, Mechanics & Astronomy最新文献

The instantaneous detection of entanglement in quantum states poses a significant challenge in the fields of quantum computation and quantum information, and there are no practical methods or tools to complete this task satisfactorily so far. We propose a sufficient and necessary criterion of k-nonseparability for any n-partite finite or infinite dimensional systems, 2 ≤ k ≤ n. This criterion serves as the foundation for a practical scheme designed to detect entanglement and k-nonseparability across multipartite finite-dimensional systems. To exemplify the application of our scheme, we have developed a software tool that facilitates swift and precise identification of entanglement, k-nonseparability, and genuine entanglement within n-qubit systems, specifically tailored for systems with 2 ≤ n ≤ 4.

Galactic-scale outflows driven by active galactic nuclei (AGNs) represent a commonly invoked feedback mechanism within galaxy evolution models. However, the interactions among interstellar gas on galactic scales, the propagation of AGN outflows, and the fundamental parameters of AGNs during their evolutionary processes remain poorly understood. Notably, powerful nuclear outflows are typically associated with the early stages of AGN activity, which are characterized by high accretion rates and weak narrow emission lines. In our analysis of a sample of quasars hosting Mg ii narrow absorption lines (NALs) obtained from the Sloan Digital Sky Survey, we identify a previously unobserved phenomenon wherein galaxy-scale inflow transitions to outflow dominance, concurrent with a notable increase in the strength of the narrow [O III] line, achieving a confidence level of 6.7σ. This indicates that while nuclear outflows diminish, galaxy-wide outflows intensify as AGNs evolve. These findings suggest that early-stage outflows interact with the interstellar medium on a galactic scale, thereby facilitating a gradual transition to galaxy-wide outflows. This provides observational support for the hypothetical multi-stage propagation of AGN outflows that globally regulates galaxy evolution.

We investigate the capabilities of space-based gravitational-wave detector networks, specifically Taiji and LISA, to measure the anisotropies in stochastic gravitational-wave background (SGWB), which are characterized by the angular power spectrum. We find that a detector network can improve the measurement precision of anisotropies by at most fourteen orders of magnitude, depending on the angular multipoles. By doing so, we can enhance our understanding of the physical origins of SGWB, both in astrophysical and cosmological contexts. We assess the prospects of the detector networks for measuring the parameters of angular power spectrum. We further find an inevitable effect of cosmic variance, which can be suppressed by a better angular resolution, strengthening the importance of configuring detector networks. Our findings also suggest a potential detection of the kinematic dipole due to Doppler boosting of SGWB.

Investigating the implications of interlayer coupling on superconductivity is vital for comprehending the intrinsic mechanisms of two-dimensional materials. Van der Waals heterojunctions have attracted extensive research owing to their exotic interlayer coupling. In this study, we investigated the natural heterostructure superconductor featuring 6R-TaS₂ via measurements of electrical resistance, the Hall effect, and in-situ synchrotron X-ray diffraction (XRD) under various pressures. The study findings show that the superconducting transition temperature (T_c) of 6R-TaS₂ in the range of 0–32.5 GPa exhibits an unusual double-dome behavior as a function of pressure, with the first and second domes in the pressure range of 0–5.3 and 6.8–32.5 GPa, respectively. At 56.6 GPa, a new superconducting phase with a T_c of 2 K was observed. The XRD results show that the singular evolution of the T_c is independent of the structural phase transition. Combining the XRD results, first-principles calculations, and Hall effect measurements, we found that different interlayer coupling effects resulted in double dome superconductivity and the re-emergence of superconducting. Our findings shed light on the pivotal role of interlayer coupling in driving the anomalous alterations in superconducting properties triggered by charge transfer and Fermi surface reconstruction and provide an alternative route for comprehending the mechanisms of superconductivity in transition metal dichalcogenides (TMDs).

Compressible wall-bounded turbulence is ubiquitously encountered in modern aerospace and mechanical industries. In this review, we summarize the current state of the literature on the flow physics of compressible wall-bounded turbulence with simple flow geometry and boundary constraints, focusing on the statistics and dynamics of coherent structures, the seemingly organized flow patterns hidden amidst the nonlinear chaotic random processes. We summarize the conclusions brought by recent year studies regarding the influences of the Mach number and wall temperature on the velocity streaks, quasi-streamwise vortices and dilatational motions in the near-wall region, and the large-scale and very-large-scale motions in the outer region, from both statistical and dynamical point of view, with the primary concern of the similarities with and disparities from those in incompressible flows.

It is well known that in one-dimensional (1D) crystalline insulators, the electric polarization is a manifestation of Berry phase, which can not be quantized by time-reversal symmetry (TRS) as in Hermitian physics TRS does not induce any topological phase in one dimension. In this paper we report that even though associated with complex eigenenergies a 1D non-Hermitian insulator obeying only TRS is capable of presenting quantized bulk polarization. The underlying physical reason is unveiled: TRS guarantees the complex energies to come in pair (E, E*), and the corresponding decaying and amplifying wave functions also come in pair and have the same variation rate, hence, giving rise to a stable wannier center. The electron transport is performed by means of charge pumping process, which verifies the physical mechanism above. At last, we discuss the possible experimental implementation of the proposed model by means of twisted-π gauge flux.

The observed timing data, magnetic tilt angle χ, and age of young pulsars could be used to probe some important issues about neutron star (NS) physics, e.g., the NS internal magnetic field configuration, and the number of precession cycles ξ. Both quantities are critical in studying the continuous gravitational wave emission from pulsars, and the latter generally characterizes the mutual interactions between superfluid neutrons and other particles in the NS interior. The timing behavior of pulsars can be influenced by the dipole field evolution, which instead of decaying, may increase with time. An increase in the dipole field may result from the re-emergence of the initial dipole field B_d,i that was buried into the NS interior shortly after the birth of the NS. In this work, the field re-emergence scenario ξ and the internal field configuration of several young pulsars, as well as their B_d,i are investigated by assuming typical accreted masses ΔM. Moreover, since the Crab pulsar has an exactly known age and its tilt angle change rate can be inferred from observations, we can set stringent constraints on its ξ, B_d,i, and ΔM. Although for other young pulsars without exactly known ages and tilt angle change rates, these quantities cannot be accurately determined, we find that their ξ are generally within ∼10⁴–10⁶, and some of them probably have magnetar-strength B_d,i. Our work could be important for investigating the transient emissions associated with NSs, the origin of strong magnetic fields of NSs, pulsar population, continuous gravitational wave emission from pulsars, and accretion under extreme conditions in principle.

In our previous work [Physical Review D, 2024, 109(4): 043009], we introduced MSNRnet, a framework integrating deep learning and matched filtering methods for gravitational wave (GW) detection. Compared with end-to-end classification methods, MSNRnet is physically interpretable. Multiple denoising models and astrophysical discrimination models corresponding to different parameter space were operated independently for the template prediction and selection. But the MSNRnet has a lot of computational redundancy. In this study, we propose a new framework for template prediction, which significantly improves our previous method. The new framework consists of the recursive application of denoising models and waveform classification models, which solve the problem of computational redundancy. The waveform classification network categorizes the denoised output based on the signal’s time scale. To enhance the denoising performance for long-time-scale data, we upgrade the denoising model by incorporating Transformer and ResNet modules. Furthermore, we introduce a novel training approach that allows for the simultaneous training of the denoising network and waveform classification network, eliminating the need for manual annotation of the waveform dataset required in our previous method. Real-data analysis results demonstrate that our new method decreases the false alarm rate by approximately 25%, boosts the detection rate by roughly 5%, and slashes the computational cost by around 90%. The new method holds potential for future application in online GW data processing.

In scenarios where a large amount of data needs to be learned, incremental learning can make full use of old knowledge, significantly reduce the computational cost of the overall learning process, and maintain high performance. In this paper, taking the MaxCut problem as our example, we introduce the idea of incremental learning into quantum computing, and propose a Quantum Proactive Incremental Learning algorithm (QPIL). Instead of a one-off training of quantum circuit, QPIL contains a multi-phase training on gradually-increased subgraphs of all vertices, proactively reducing large-scale problems to smaller ones to solve in steps, providing an efficient solution for MaxCut. Specifically, some vertices and corresponding edges are randomly selected for training to obtain optimized parameters of the quantum circuit at first. Then, in each incremental phase, the remaining vertices and corresponding edges are gradually added and the parameters obtained from the previous phase are reused in the parameter initialization of the current phase. We perform experiments on 120 different small-scale graphs, and it shows that QPIL performs superior to prevalent quantum and classical baselines in terms of approximation ratio (AR), time cost, anti-forgetting, and solving stability. In particular, QPIL’s AR surpasses 20% of mainstream quantum baselines, and the time cost is less than 1/5 of them. The idea of QPIL is expected to inspire efficient and high-quality solutions in large-scale MaxCut and other combinatorial optimization problems.

Connectivity of two-qubit logic gates plays a crucial and indispensable role in quantum computation research. For the cold atom qubit platform, while the two-qubit Rydberg blockade gate has recently made rapid experimental progress, a pressing challenge is to improve connectivity in pursuit of genuine scalability without sacrificing speed or fidelity. A significant advancement in this direction can be achieved by introducing an extra buffer atom to extend the two-qubit gate beyond purely nearest-neighbor two-body interactions. The buffer atom couples with the two qubit atoms through nearest-neighbor interactions, even though the qubit atoms do not directly exert any physical influence on each other. The established method of off-resonant modulated driving (ORMD) is not only convenient but also lays the groundwork for this latest development. Although the atomic linkage structure here exhibits more complex interactions compared to previous two-body systems, the population can satisfactorily return to the ground state after the ground-Rydberg transition with a properly designed modulation waveform. This can be achieved through one-photon and two-photon ground-Rydberg transitions in common practices. Furthermore, with buffer atom relay or similar structures, it is possible to realize a two-qubit entangling gate between two distant qubit atoms. In addition to demonstrating that such solutions are feasible, the representative modulation patterns are analyzed, showcasing the versatility of buffer-atom-mediated two-qubit gates. From a broader perspective, these efforts enhance the resemblance between the cold atom qubit platform and the superconducting qubit system, with the buffer atom functioning like wires and junctions.