Science China Physics, Mechanics & Astronomy最新文献

Quantum secure direct communication (QSDC) promotes high security and instantaneousness in communication by conveying secret messages directly via the quantum channel. In particular, the continuous variable (CV) scheme of QSDC is already compatible with current room-temperature telecommunication networks and is very robust to the free-space background noise, making it a unique choice in certain applications. However, to date, the security proofs of CV-QSDC are poorly advanced, as the eaves-dropper Eve in these proofs is limited, either can not apply the optimal collective measurements, or does not have full access to the quantum channel. In this paper, we refine and advance the previous theory in this area, providing a tight secrecy capacity bound for the CV-QSDC protocol. We study the secrecy capacity achievable by the two-step scheme, for both (one-mode) collective Gaussian attack and two-mode Gaussian attack, from the standard Markovian assumption on the environment to a more challenging scenario with a time-like and spatial non-Markovian model. Numerical results show that the best attack strategy for Eve is the entangled attack using maximally entangled states (with a positive correlation parameter). More interestingly, we find that the protocol with the standard Markovian model can, in theory, achieve a longer transmission distance in the communication channel affected by high thermal noise.

In this work, we introduce a novel framework to investigate ringdown gravitational waveforms in the presence of dynamical matter fields outside the horizon of a black hole. We systematically analyze two distinct scenarios of dynamical matter fields: motion along geodesics and uniform motion with constant velocity. Our results reveal rich phenomena in the ringdown gravitational wave signals, including the suppression or enhancement of echoes, frequency shifts in the decay oscillations, and intricate modulations of the power-law tails. Notably, we demonstrate that subluminal moving potentials can produce irregular echo patterns and shift the dominant frequencies, offering potential new observational signatures beyond the already-known ringdown analyses. This study provides a new perspective for probing dynamic environments around black holes and offers a theoretical foundation for interpreting possible deviations in future gravitational wave detections.

Majorana zero modes (MZMs), promising for topological quantum computation, are naturally hosted in vortices of two-dimensional topological superconductors (TSCs). However, precise control and braiding of these vortex-bound MZMs remain a significant challenge. This work proposes and numerically demonstrates a novel braiding scheme utilizing a programmable matrix of spintransfer torque (STT) devices (STT-matrix) integrated with a TSC layer. By selectively activating individual STT elements, their localized stray fields enable deterministic manipulation, including driving, braiding, and fusion, of superconducting vortices and their associated MZMs. We establish a comprehensive simulation framework combining finite element analysis for STT-induced vortex formation, time-dependent Ginzburg-Landau equations for vortex dynamics and time-dependent Bogoliubov-de Gennes equations for MZM evolution. Simulations confirm the STT-matrix’s capability for high-fidelity vortex manipulation and demonstrate MZM braiding dynamics. We quantify the impact of vortex acceleration and finite MZM coupling on braiding fidelity, showing that it can be optimized by adjusting STT spacing and vortex separation. Furthermore, we demonstrate controlled MZM fusion and measure the resultant energy splitting. This STT-matrix-based approach offers a highly versatile, scalable, and potentially practical platform for operating MZMs within TSC vortices, advancing the development of fault-tolerant topological quantum computation.

Spatiotemporally varying media, which simultaneously modulating both in space and time, offer a versatile platform for dynamic control of electromagnetic waves. The multimode properties of such media are crucial for applications in quantum simulation, large-scale optical computing, and high-capacity communication systems. Here, we present a reconfigurable approach for applying spatiotemporal electromagnetic modulation in a substrate-integrated waveguide (SIW), enabling the resolution and engineering of multiple modes in spacetime crystals (STCs). We begin by demonstrating the diffraction of Floquet modes in a time crystal, analogous to a time grating. By superimposing spatial modulation, we impart additional momentum to these modes, allowing the Floquet modes to radiate into free space at distinct, angle-resolved directions. Furthermore, by incorporating multicolor spatiotemporal modulation, we achieve precise control over the Floquet-Bloch modes, facilitating multi-user video distribution. Our approach paves the way for the engineering of multiple Floquet-Bloch modes in STCs, offering promising prospects for quantum simulation, optical computing, and next-generation wireless communications.

Chiral and nonreciprocal quantum devices are crucial for signal routing and processing in a quantum network. In this work, we study the chirality and nonreciprocity of a giant atom coupled to a one-dimensional waveguide. We clarify that the chiral emission of the giant atom is not directly related to the time-reversal symmetry breaking but to the mirror-symmetry breaking. We propose a passive scheme, by extending the legs of the giant atom, to realize the chiral emission without breaking time-reversal symmetry. We prove that the time-reversal symmetry breaking alone via nonuniform coupling phases is not sufficient for the nonreciprocal single-photon scattering of the giant atom. The nonreciprocity needs both the time-reversal symmetry breaking and the finite external dissipation of the giant atom. Our work clarifies the roles of symmetries in the chirality and nonreciprocity of giant-atom systems and paves the way for the design of on-chip functional devices with superconducting giant atoms.

Recently, the films of the Ruddlesden-Popper (RP) nickelate superconductors, in which the (La,Pr)₃Ni₂O₇ system exhibits a remarkable transition temperature T_c exceeding 40 K, were synthesized at ambient pressure. We systematically investigate the band structures and electronic correlation effects to identify the key factors controlling superconductivity and pathways to enhance T_c. Based on density functional theory (DFT) calculations, we construct a bilayer two-orbital ((3d_{{3{z}^{2}}-{r}^{2}}) and (3d_{{{x}^{2}}-{y}^{2}})) tight-binding model for a series of in-plane compression mimicking the substrate effect. We find the band energy at the M point drops with the compression, leading to an increase in the density of states at the Fermi level, in stark contrast to the behavior of the bulk under pressure. We then apply the functional renormalization group (FRG) method to study the electronic correlation effect on the superconductivity. We find the s_±-wave pairing symmetry remains robust in the films, the same as the bulk. But somewhat surprisingly, for the films, we find T_c can be enhanced by reducing the in-plane lattice constant, increasing the out-of-plane lattice constant, or further electron-doping. These findings are consistent with the itinerant picture of the superconductivity induced by spin-fluctuations and provide theoretical support for further boosting T_c in future experiments.

The growing usage of industrial dyes makes the sewage treatment a global issue, therefore low-cost, highly efficient catalysts are urgently demanded for wastewater purification. We present an ultrasonic-engineered catalytic technology, which can achieve an extremely high efficiency in azo dye degradation via a tiny dosage of 0.1 g L⁻¹ (only one-fifth of the normally used dosage) Fe₈₁Si₉B₁₀ amorphous powders (APs) with a low activation energy of 45.32 kJ mol⁻¹ and a high reaction rate of 0.70291 min⁻¹. The non-destructive ultrasonic vibration (UV) treatment with very short processing times (0.43–1.08 s) amplifies degradation efficiency by an astonishing 55-fold compared to untreated APs. Combined with high-energy X-ray diffraction and small-angle neutron scattering analyses, we reveal that the UV-induced structural reconstruction at both short- and medium-range order effectively lower reaction energy barriers while accelerating charge transfer kinetics. The high-energy ultrasonic attacks promote the exposure of massive fresh active sites, which enhance the Fe²⁺/Fe³⁺ redox circulation and thereby lead to the fast Fenton-like oxidation processes. By integrating ultrasonic physics with amorphous materials, this work develops an energy-efficient catalytic activation method, enabling sustainable water purification and innovative pollutant treatment strategies.

Accurate targeting is critical for the effectiveness of transcranial focused ultrasound (tFUS) neuromodulation. While CT provides accurate skull acoustic properties, its ionizing radiation and poor soft tissue contrast limit clinical applicability. In contrast, MRI offers superior neuroanatomical visualization without radiation exposure but lacks skull property mapping. This study proposes a novel, fully CT-free simulation framework that integrates MRI-derived synthetic CT (sCT) with efficient modeling techniques for rapid and precise tFUS targeting. We trained a deep-learning model to generate sCT from T1-weighted MRI and integrated it with both full-wave (k-Wave) and accelerated simulation methods—hybrid angular spectrum (kW-ASM) and Rayleigh-Sommerfeld ASM (RS-ASM). Across five skull models, both full-wave and hybrid pipelines using sCT demonstrated sub-millimeter targeting deviation, focal shape consistency (FWHM ∼3.3–3.8 mm), and <0.2 normalized pressure error compared to CT-based gold standard. Notably, the kW-ASM and RS-ASM pipelines reduced simulation time from (∼3320 ±1270) to (187±27) and (345±85) s respectively, achieving ∼94% and ∼90% time savings. These results confirm that MRI-derived sCT combined with innovative rapid simulation techniques enables fast, accurate, and radiation-free tFUS planning, supporting its feasibility for scalable clinical applications.

The performance sensitivity of quasi-zero-stiffness (QZS) isolators to load-position mismatches poses significant challenges and hinders their practical implementation. Herein, a translation-scaling coordinated transformation method is proposed for decoupled adjustment of the rated load and equilibrium position. By coordinating translation and scaling transformations of negative and positive stiffnesses, the rated load and equilibrium position can be independently tuned, thereby mitigating performance sensitivity under time-varying operating conditions. Based on this method, a load-position decoupled QZS isolator (LPD-QZS) is developed and systematically investigated. A liftable nested magnet-coil pair is employed to generate translatable and scalable negative stiffness, while an end-to-end magnet-coil pair combined with a membrane spring pair provides nonuniformly scalable positive stiffness. Analyses reveal and verify the tunable stiffness characteristics and the effectiveness of the translation-scaling coordinated transformation in achieving load-position decoupled adjustment, as well as the distinctive behavior arising from it. Finally, offline and online tests are conducted to evaluate the robustness of the LPD-QZS under varying rated loads and equilibrium positions. Sweep excitation tests indicate that the LPD-QZS exhibits excellent low-frequency vibration isolation performance, with a low isolation frequency starting from 3.3 Hz, in drastic contrast with the degraded performance without load-position decoupled adjustment under load-position mismatches. Significantly, through translation-scaling coordinated transformation, the LPD-QZS preserves its QZS characteristic across various applied loads and operating positions, highlighting its potential for practical engineering applications, particularly in multi-leg QZS platforms.