Science China Physics, Mechanics & Astronomy最新文献

It has been demonstrated that the Rydberg criticality in a many-body atomic system can enhance the measurement sensitivity of the microwave electric field by increasing the Fisher information. In our previous work, we proposed and experimentally verified that the Fisher information near the critical point can be increased by more than two orders of magnitude with the Rydberg atoms coupled with an optical cavity compared with that in free space. Here we demonstrate the precision measurement of the microwave electric field by cavity-enhanced critical behavior. We show that the equivalent measurement sensitivity of the microwave electric field can be enhanced by an order of magnitude compared with that in free space. The obtained sensitivity can be enhanced to 2.6 nV cm⁻¹ Hz^−1/2.

Understanding the nature of primordial fluctuations is pivotal to unraveling the Universe’s early evolution. While these fluctuations are observed to be nearly scale-invariant, quasi-adiabatic, and Gaussian on large scales, their small-scale behavior remains poorly constrained, offering a potential window into new physics. Recent detections of a stochastic gravitational wave background in the nanohertz frequency range by pulsar timing arrays (PTAs), including NANOGrav, PPTA, EPTA+InPTA, and CPTA, align with astrophysical predictions from supermassive black hole binaries but could also encode signatures of primordial phenomena. We investigate whether the observed signal originates from primordial isocurvature or adiabatic fluctuations by fitting them to the latest NANOGrav dataset. Through comprehensive Bayesian model comparison, we evaluate the distinguishability of these scenarios given current PTA sensitivities. Our results demonstrate that existing data cannot conclusively differentiate between isocurvature and adiabatic sources, highlighting the need for enhanced observational capabilities to probe the primordial universe at small scales.

Recent pulsar timing observations using MeerKAT of the eccentric binary millisecond pulsar, PSR J0514–4002E, have unveiled a companion with a mass in the mass gap, ranging from 2.09 M_⊙ to 2.71 M_⊙. This challenges conventional astrophysical scenarios for black hole formation. In this paper, we present an alternative explanation: PSR J0514–4002E could be in a PBH-NS binary, with the companion potentially being a primordial black hole formed during the early Universe’s first-order phase transition. The associated stochastic gravitational-wave background generated during this phase transition can account for the observed signal from the pulsar timing array, and the abundance of primordial black holes is consistent with constraints from LIGO-Virgo-KAGRA.

As China’s first X-ray astronomy satellite, the hard X-ray modulation telescope (Insight-HXMT) carries three sets of X-ray telescopes. The high energy X-ray telescope (Insight-HXMT/HE) could serve as an all-sky gamma-ray monitor with a detection area of up to 5000 cm² and energy range from about 200 keV to 3 MeV. These characteristics, together with the high orbital inclination angle (43°) of the satellite, make the HE very suitable for detecting terrestrial gamma-ray flashes (TGFs). In this work, we implemented a dedicated TGF search algorithm for Insight-HXMT/HE, and identified 282 bright TGFs in its first four years of operation. We made a systematic study on the properties of these TGFs, including trigger time, duration, intensity, as well as the lightning association. We found that TGFs detected in mid-latitude regions (30° to 43°) are rare and they do not exhibit significantly different properties compared with TGFs in low-latitude (within 30°). Interestingly, the hardness ratio of TGF measured by Insight-HXMT/HE seems to be independent of the TGF duration, which differs from previous studies. These results show that, despite the dedicated design for astronomical observation, Insight-HXMT/HE is a versatile instrument to study energetic radiation phenomena from the Earth.

Wheeler’s delayed-choice experiment demonstrates wave-particle duality of particles using different experimental configurations of a Mach-Zehnder interferometer. In a quantum version of this experiment, the wave-particle behaviour of photons can be observed by controlling presence or absence of the second beam splitter. Here, we implement a delayed-choice experiment with dual selections based on entangled photons, experimentally controlling both of two beam splitters in the Mach-Zehnder interferometer, where the presence and absence of the second beam splitter are simultaneously controlled through path encoding. Our experiment reveals the wave-particle behavior of single photons under different configurations of two beam splitters. We further discuss the scenario when two beam splitters are in a quantum superposition of being present and absent, photons will be in a wave-particle quantum superposition state.

Exceptional points (EPs) have extensive and important applications in many wave-based technologies, such as ultra-sensitive sensing, unidirectional scattering and low-threshold laser. However, most of the previous EP-related wave phenomena are demonstrated in systems with fixed configuration, thereby extremely constraining their adaptability and reconfigurability in practice. Here, we introduce a flexible approach to tuning EPs in an acoustic system with sandwich structures. A rotatable component, associated with an alterable gradient index, is clamped by a pair of lossy acoustic resonators. Theoretical derivations and numerical simulations validate the capabilities of the model in continuously regulating EPs in the parameter space, with ingenious experimental setups confirming these findings. The results showcase the system’s effectiveness in achieving unidirectional reflectionless wave propagation across various frequencies. Our research reveals a flexible approach to linking the adjustment of EPs to a simple structural parameter, offering a robust framework for exploring and implementing non-Hermitian wave phenomena in practical scenarios.

Recently, it has been discovered that the nonlinear self-interaction of matter can induce energy extraction from black holes beyond superradiant instability. This process is closely associated with the occurrence of a dynamical first-order transition between different types of static black holes. To explore whether first-order phase transitions invariably lead to energy extraction, we have investigated the evolution of black holes in the Einstein-Maxwell-scalar model with a higher-order coupling. In this model, there are also dynamical first-order phase transitions between black hole solutions. Our findings indicate that energy can only be extracted from a small, stable hairy black hole in this model. However, this energy extraction is more closely related to the growth of the black hole horizon radius, rather than the dynamical transition between different types of black holes. This suggests that a dynamical first-order phase transition does not necessarily result in energy extraction.

We propose a novel criterion to identify the first-order QCD phase transition and the critical end-point (CEP) via directly the net-proton number fluctuations measured in relativistic heavy-ion collision (RHIC) experiments. Using this method, we show that there has not yet been a direct signal of the CEP of QCD according to the currently available data accumulated in the beam energy scan experiments with (sqrt{s_{text{NN}}};geqslant;7.7) GeV. However, there is still a possibility for the CEP to appear in the matter generated by the collisions with energy below 7.7 GeV, and its identification requires future measurements with high statistics for the high-order cumulants at low collision energies.

Transparent silicon nitride ceramics with good optical and mechanical properties are promising ceramics for scientific and industrial window materials with a long service life. The optical transparency and mechanical strength will be substantially enhanced in dense nano-polycrystalline monoliths. However, the synthesis of nano-polycrystalline α-Si₃N₄ has not been realized due to the limitations of conventional sintering techniques. Here, nano-polycrystalline α-Si₃N₄ was prepared by direct conversion of micron-grain silicon nitride without additives under high-pressure conditions of 5 GPa and a limited temperature range 1650°C–1700°C. The micron-sized grains undergo grain refinement and recrystallization to form uniform nano-grains under high pressure and high temperature. Furthermore, transparent α-Si₃N₄ samples exhibit the highest Vickers hardness of 26.7 GPa, which is far higher than that of specimens with or without additives used in other sintering methods (e.g., SPS, and HP). According to the Hall-Petch and Taylor dislocation hardening effects, the refined nano-grains, coherent grain boundaries, and high dislocation density lead to high hardness. Moreover, the high density, nanoscale grains, and fine grain boundaries are ascribed to the improvement of transparency. Ultrahigh-pressure sintering induces grain refinement, grain coherency, and increased dislocation in silicon nitrides, thus providing a promising method for preparing advanced transparent ceramic windows in the future.

Cavity magnomechanics, leveraging magnetostrictive interactions, has emerged as an important platform for implementing spin-based precision measurement and investigating macroscopic quantum phenomena. Due to the weakness of the intrinsic magnetostrictive effect, the coupling between magnetic and mechanical vibrations in typical magnomechanical systems is relatively small. Here, we develop a center-of-mass magnomechanical system that is non-reliant on magnetostrictive effects. The proposed system consists of an inhomogeneous magnetic field and a yttrium iron garnet (YIG) sphere that is harmonically confined. We theoretically investigate the interaction between center-of-mass motion and magnonic excitation of the YIG sphere, and find that the field inhomogeneity induces a static force on the YIG sphere. Consequently, a magnomechanical interaction between the center-of-mass motion and the magnonic excitation is established. The parameter optimization of the magnomechanical interaction has been performed, and we show that the proposed system has the potential to reside in both the single-magnon high-cooperativity regime and the sideband-resolved regime. The capabilities of the system for magnomechanical applications, such as ground-state cooling of the mechanical mode, have been discussed, and we show that ground-state cooling of the mechanical mode is feasible in the unresolved sideband regime by taking into account the magnonics Kerr effect. Our analysis holds great promise for achieving magnonic nonlinearity at low excitation levels, thereby opening up avenues for magnomechanical applications in precision measurements and quantum manipulation.