Science China Physics, Mechanics & Astronomy最新文献

Quantum two-way time transfer (Q-TWTT) leveraging energy-time entangled biphotons has achieved sub-picosecond stability but faces fundamental distance limitations due to the no-cloning theorem’s restriction on quantum amplification. To overcome this challenge, we propose a cascaded Q-TWTT architecture employing relay stations that generate and distribute new energy-time entangled biphotons after each transmission segment. Theoretical modeling reveals sublinear standard deviation growth (merely (sqrt{N}times) increase for N × equidistant segments), enabling preservation of sub-picosecond stability over extended distances. We experimentally validate this approach using a three-station cascaded configuration over 2×100 km fiber segments, demonstrating strong agreement with theory. Utilizing independent Rb clocks at end and relay stations with online frequency skew correction, we achieve time stabilities of 3.82 ps at 10 s and 0.39 ps at 5120 s. The consistency in long-term stability between cascaded and single-segment configurations confirms high-precision preservation across modular quantum networks. This work establishes a framework for long-distance quantum time transfer that bypasses the no-cloning barrier, providing a foundation for future quantum-network timing infrastructure.

The Unruh effect predicts an astonishing phenomenon that an accelerated detector would detect counts despite being in a quantum field vacuum in the rest frame. Since the required detector acceleration for its direct observation is prohibitively large, recent analog studies on quantum simulation platforms help to reveal various properties of the Unruh effect and explore the not-yet-understood physics of quantum gravity. To further reveal the quantum aspect of the Unruh effect, analogous experimental exploration of the correlation between the detector and the field, and the consequences for coherent quantum trajectories of the detector without classical counterparts, are essential steps but are currently missing. Here, we utilize a laser-controlled trapped ion to experimentally simulate an oscillating detector coupled with a cavity field. We observe joint excitation of both the detector and the field in the detector’s frame, coincide with the coordinated dynamics predicted by the Unruh effect. Particularly, we simulate the detector moving in single and superposed quantum trajectories, where the latter case shows coherent interference of excitation. Our demonstration reveals properties of quantum coherent superposition of accelerating trajectories associated with quantum gravity theories that have no classical counterparts, and may offer a new avenue to investigate phenomena in quantum field theory and quantum gravity. We also show how a generalization of the method and results in this work may be beneficial for direct observation of the Unruh effect.

Current gravitational-wave detectors have achieved remarkable sensitivity around 100 Hz, enabling ground-breaking discoveries. Enhancing sensitivity at higher frequencies in the kilohertz (kHz) range promises access to rich physics, particularly the extreme conditions during the merger stage of binary neutron stars. However, the high-frequency sensitivity of Michelson-based interferometers is fundamentally limited by their linear optical cavities, which are optimized for low-frequency signal enhancement. A new configuration employing an L-shaped optical resonator was proposed to overcome this limitation, offering exceptional sensitivity in the kHz band. As a pathfinder, the 12-meter prototype at Beijing Normal University is designed to demonstrate the sensing and control schemes of this new kHz detector configuration and to explore its performance in the high-power regime with suspended optics. Beyond its primary scientific goal, the prototype also offers potential sensitivity in the megahertz (MHz) range, potentially enabling constraints on exotic sources. This paper presents an overview of the prototype, including its optical design and current development status of key components.

In this study, we propose an effective strategy for selecting alloying elements to suppress hydrogen diffusion in γ-uranium (γ-U) based on the first-principles investigation of the Niobium (Nb) influences on hydrogen diffusion behavior. The simulation results show that the substitution of Nb in the body-centered cubic (bcc) lattice of γ-U significantly reduces the hydrogen diffusion rate, driven by two key factors: the thermodynamic stabilization of the γ-U bcc lattice and Nb’s strong hydrogen trapping effect. Diffusion energy pathway and electronic structure analyses reveal the presence of energy wells around Nb atoms, causing hydrogen to form cage-like diffusion pathways centered on Nb atoms, which effectively restricts long-range hydrogen diffusion in γ-U. Although Nb’s hydrogen trapping ability decreases at higher hydrogen concentrations, it still plays a crucial role in preventing the nucleation of UH₃. Based on these findings, we propose a strategy for predicting hydrogen diffusion kinetics in a series of U-X (X = Ti, Tc, Nb, Mo, Re, Zr, In, Tl) alloys using first-principles static calculations, and establish a near-linear correlation between diffusion energy barriers, X-H bond lengths, and alloy formation energies. Our study underscores the importance of first-principles calculations in selecting suitable alloying elements to regulate hydrogen diffusion in uranium alloys, offering valuable insights with significant implications for engineering applications.

Time-delay interferometry (TDI) is essential for suppressing laser frequency noise in space-based gravitational wave (GW) observatories such as LISA. However, current second-generation TDI schemes often exhibit undesirable null frequencies and require long delay spans, which can impair data analysis performance. In this work, we introduce an alternative TDI configuration—PD4L—designed to minimize null frequencies and operate with a shorter effective time span. Constructed by synthesizing two distinct first-generation TDI schemes, PD4L achieves a delay span of 4L (where L is the arm length), half that of the standard Michelson and hybrid Relay configurations. We assess PD4L’s performance by evaluating the spectral stability of instrumental noise via arm-length derivatives, simulating chirping GW signals from coalescing massive black hole binaries, and comparing waveform responses. Parameter estimation is performed in the frequency domain, and noise characterization is examined under realistic orbital dynamics. As demonstrated by the comparisons, the compact structure of PD4L offers several advantages: (1) reduced data margins at segment boundaries, (2) mitigated aliasing effects in the high-frequency regime, and (3) shortened signal tails arising from extended delay spans. Additionally, PD4L’s null channels exhibit the same minimal null frequencies as its science channels, while maintaining greater spectral stability than other null streams. Overall, PD4L improves parameter estimation accuracy at high frequencies and supports reliable noise characterization over observation periods of up to four months. These results highlight PD4L as a compact and effective alternative for future TDI implementations, especially in high-frequency GW data analysis for LISA-like missions.

In this paper, we investigate the electromagnetic form factors (EMFFs) and charge radii of pseudoscalar mesons within the light-front quark model (LFQM). Using parameters derived from the confinements of mesonic decay constants, we obtain numerical results, which indicate the following: (1) the EMFFs of charged and neutral mesons exhibit significant differences in their endpoint behaviors but show similar asymptotic behavior in the momentum transfer regions Q² > 2 GeV². For the EMFFs of light mesons such as π and K⁺, our results are in excellent agreement with experimental data in the small momentum transfer regions (Q² < 0.3 GeV²). For the charge radii of mesons, our results also show rough consistency with predictions from other approaches. (2) For charged mesons, the peak values of Q²F_P(Q²) are approximately proportional to the mass difference Δm between their constituent quarks. Moreover, the mean square radii 〈r²〉_P of charged mesons decrease with increasing meson mass and decreasing Δm. For neutral mesons, their charge radii are primarily determined by the electric charge of the heavy quark. These results indicate that quark mass asymmetry significantly influences the behavior of the EMFFs and charge radii of mesons. Experimental data to test these predictions would thus be of great interest.

Previously identified integrable boundary states in ABJM theory are exclusively achiral. This paper presents the first chiral integrable boundary states in the SU(4) alternating spin chain from the planar two-loop dilatation operator in the scalar sector. Utilizing a sufficient condition for the untwisted integrable condition, we identify specific two-site and four-site basis boundary states as chiral integrable states. Numerical evidence indicates that other basis states are unlikely to be chiral integrable. Furthermore, we compute the overlaps between these chiral integrable basis states and on-shell Bethe eigenstates.

Additively manufactured (AM) austenitic stainless steel (ASS, e.g., 316LSS) potentially exhibits excellent strength-ductility synergy in which the deformation-induced martensitic transformation (DIMT) is decisive. However, the DIMT mechanism is still elusive for AM 316LSS. Here we decipher the role of twin boundary (TB) and grain boundary (GB) in governing the DIMT behavior as well as the associated atomic-scale mechanism by characterization-informed atomistic simulations. Experimental characterizations of DIMT in AM 316LSS show martensite distributed near TBs under quasi-static (QS) tension, but closely related to GBs under high strain rate (HSR) tension. Informed by characterizations, atomistic models covering grain sizes, GB angles and TBs are then constructed to reveal the effect of GBs and TBs on DIMT behavior. It is found that the low-angle GB (LAGB) and small grain size in AM 316LSS suppress DIMT, whereas the synergistic effect of high-angle GB (HAGB) and large grain size (e.g., in wrought 316LSS) results in large-area DIMT. When TBs exist in the 316LSS grains, TBs can promote intragranular DIMT to make DIMT independent of GB angle and grain size, agreeing with DIMT observed in both wrought and AM 316LSS under QS tension. This is ascribed to the TBs-nearby heavy strain concentration that easily results in DIMT behavior and the TBs-nearby atoms that satisfy the Nishiyama-Wasserman relationship for triggering DIMT nucleation within the grain. In contrast, HAGBs dominate DIMT behavior in models without TBs owing to the GBs-nearby local lattice distortion that satisfies the Kurdjumov-Sachs relationship for allowing phase transformation. There are almost no HAGBs and thus an ignorable DIMT in AM 316LSS, agreeing with the experimental HSR tension results. These findings should shed light on the DIMT mechanism in AM 316LSS and help the design of AM 316LSS with improved mechanical performance.

Entanglement-enhanced quantum sensors encounter a fundamental trade-off: while entanglement improves precision to the Heisenberg limit, it restricts dynamic range. To address this trade-off, we present a credible-interval-based adaptive Bayesian quantum frequency estimation protocol for Greenberger-Horne-Zeilinger (GHZ)-state-based atomic clocks. Our method optimally integrates prior knowledge with new measurements and determines the interrogation time by correlating it with the period of the likelihood function, based on Bayesian credible intervals. Our protocol can be implemented using either individual or cascaded GHZ states, thereby extending the dynamic range without compromising Heisenberg-limited sensitivity. In parallel with the cascaded-GHZ-state protocol using fixed interrogation times, the dynamic range can be extended through an interferometry sequence that employs individual GHZ states with variable interrogation times. Furthermore, by varying the interrogation times, the dynamic range of the cascaded-GHZ-state protocol can be further extended. Crucially, our protocol enables dual Heisenberg-limited precision scaling ∝ 1/Nt in both particle number N and total interrogation time t, surpassing the hybrid scaling (infty 1/Nsqrt{t}) of the conventional cascaded-GHZ-state protocol. While offering a wider dynamic range, the protocol is more stable against noise and more robust to dephasing than existing adaptive schemes. Beyond atomic clocks, our approach establishes a general framework for developing entanglement-enhanced quantum sensors that simultaneously achieve both high precision and broad dynamic range.