Science China Physics, Mechanics & Astronomy最新文献

Converting magnetization spin to orbital current often relies on strong spin-orbit interaction that may cause additional angular momentum dissipation. We report that coherent magnetization dynamics in magnetic nanostructures can evanescently pump an orbital current into adjacent semiconductors due to the coupling between their stray electromagnetic field and electron orbitals without relying on spin-orbit coupling. The underlying photonic spin of the electromagnetic field governs the orbital polarization that flows along the gradient of the driven field. Due to the joint effect of the electric and magnetic fields, the orbital Hall current that flows perpendicularly to the gradient of the time-varying field is also generated and does not suffer from the orbital torque. These findings extend the paradigm of orbital pumping to include photonic angular momentum and pave the way for developing low-dissipation orbitronic devices.

In this article, we propose that superradiant echoes can be achieved at room temperature by applying a laser illumination and a microwave Hahn echo sequence to a diamond with a high concentration of nitrogen-vacancy (NV) centers placed in a dielectric microwave cavity. We identify that the combined action of two microwave driving pulses and a free evolution imprints a frequency grating among NV spin sub-ensembles, and the multiple re-phasing of the grated spin sub-ensembles leads to multiple superradiant echoes through a collective coupling with the cavity. Furthermore, we show that the superradiant echoes can be actively tailored through the microwave pulses and the laser illumination by adjusting the grating parameters, and the multiple re-phasing dynamics is analogous to the one leading to superradiant beats in atomic optical clock systems. In the future, the spin sub-ensembles grating and the resulting echoes can be further optimized with dynamical decoupling, which might pave the way for applications in quantum sensing.

X-ray pulsars (XRPs) consist of a magnetized neutron star (NS) and an optical donor star. The NS accretes matter from the donor star, producing pulsed X-ray emission. In most cases, the donor stars are Be stars, and accretion is episodic, that is, the NSs are generally X-ray dim but occasionally experience outbursts. Here, we carry out a statistical study with the X-ray monitoring data and obtain strong correlations between the spin periods of the NSs and the outburst parameters for the first time. We show that XRPs containing faster rotating NSs tend to display more violent eruptions. In addition, pulsating ultraluminous X-ray sources in nearby galaxies follow a similar relationship. We demonstrate that most of these systems are close to the spin equilibrium, and that brighter pulsars have acquired more angular momentum by accreting matter from their companion stars, resulting in faster rotating NSs.

Non-Hermitian (NH) systems can display exceptional topological defects without Hermitian counterparts, exemplified by exceptional rings in NH two-dimensional systems. However, exceptional topological features associated with higher-dimensional topological defects have only recently come into attention. We here investigate the topology of the singularities in an NH three-dimensional system. We find that the third-order singularities in the parameter space form an exceptional surface (ES), on which all three eigenstates and eigenenergies coalesce. Such an ES corresponds to a two-dimensional extension of a point-like synthetic tensor monopole. We quantify its topology with the Dixmier-Douady invariant, which measures the quantized flux associated with the synthetic tensor field. We further propose an experimentally feasible scheme for engineering such an NH model. Our results pave the way for investigations of exceptional topology associated with topological defects with more than one dimension.

The preservation of quantum coherence is besieged by a fundamental dogma: its revival necessitates non-Markovian memory effects from structured environments. This paradigm has constrained quantum control strategies and obscured simpler paths to coherence protection. Here, we shatter this belief by demonstrating unambiguous coherence revival even in strictly Markovian regimes, achieved solely through basis engineering in the σ_x/σ_y bases. We establish a comprehensive analytical framework for predictive coherence control, delivering three universal design principles. First, we derive a minimum critical noise based frequency, (omega_{0}^{c} approx {pi over {t_{rm max}}}) serving as a universal criterion for engineering non-Markovian dynamics over any interval [0, t_max]. Crucially, we show that Markovian environments (ω₀ < ω ^c₀ ) can exhibit coherence revival when the Zeeman energy satisfies ω_k > π/(2t_max), establishing basis engineering as an independent control dimension that separates revival dynamics from environmental memory. Furthermore, for non-Markovian environments, we provide exact conditions for periodic and complete revival: setting ω₀ = n · 6.285/t_max guarantees revival in the σ_z basis, while combining it with ω_k = πω₀/6.285 ensures perfect revival in the σ_x/σ_y bases. Our results, validated by rigorous quantum simulations, provide a predictive toolkit for coherence control, offering immediate strategies for enhancing quantum memory, sensing, and error mitigation.

In quantum information processing, the development of fast and robust control schemes remains a central challenge. Although quantum adiabatic evolution is inherently robust against control errors, it typically demands long evolution times. In this work, we propose to achieve rapid adiabatic evolution, in which nonadiabatic transitions induced by fast changes in the system Hamiltonian are mitigated by flipping the nonadiabatic transition matrix using π pulses. This enables a faster realization of adiabatic evolution while preserving its robustness. We demonstrate the effectiveness of our scheme in both two-level and three-level systems. Numerical simulations show that, for the same evolution duration, our scheme achieves higher fidelity and significantly suppresses nonadiabatic transitions compared to the traditional STIRAP protocol.

Complex numbers are theoretically proved and experimentally confirmed as necessary in quantum mechanics and quantum information, and a resource theory of imaginarity of quantum states has been established. In this work, we establish a framework to quantify the imaginarity of quantum operations from the perspective of the ability to create or detect imaginarity, following the idea by Theurer et al. (Phys. Rev. Lett. 122, 190405 (2019)) used in coherence theory. We introduce two types of imaginarity measures of quantum operations based on the norm and the weight, investigate their properties and relations, derive the analytical formulas of the measure under the trace norm for qubit unitary operations, and present some applications in the tasks of channel discrimination and the entanglement-assisted exclusion. The results provide new insights into the imaginarity of operations and deepen our understanding of dynamical imaginarity.

Gravitational wave (GW) observations are expected to serve as a powerful and independent probe of the expansion history of the universe. By providing direct and calibration-free measurements of luminosity distances through waveform analysis, GWs provide a fundamentally different and potentially more robust approach to measuring cosmic-scale distances compared to traditional electromagnetic (EM) observations, which is known as the standard siren method. In this review, we present an overview of recent developments in GW standard siren cosmology, including up-to-date H₀ constraints: the re-analysis bright siren GW170817 (H_{0}=78.4_{-12.0}^{+25.7}text{km s}^{-1} text{Mpc}^{-1}) (employing the same methodology as the O4a dark and spectral siren studies), the most recent O4a dark-siren analysis (H_{0}=81.6_{-15.9}^{+21.5}text{km s}^{-1} text{Mpc}^{-1}), and their combination (H_{0}=76.6_{-9.5}^{+13.0}text{km s}^{-1} text{Mpc}^{-1}), and prospects for constraining cosmological parameters using future GW detections (H₀ is expected to be constrained to the sub-percent level in a 10-year observation of the third-generation GW detectors). We first introduce standard sirens based on how redshift information is obtained and outline the Bayesian framework used in cosmological parameter estimation. We then review the measurements on the Hubble constant from the LIGO-Virgo-KAGRA network and present the potential role of future standard siren observations in cosmological parameter estimations. A central focus of this review is the unique ability of GW observations to break cosmological parameter degeneracies inherent in the EM observations. Since the cosmological parameter degeneracy directions of GW and EM observations are quite different (roughly orthogonal in some cases), their combination can significantly improve constraints on cosmological parameters. This complementarity is expected to become one of the most critical advantages for GW standard siren cosmology. We also briefly highlight the impact of systematic uncertainties, such as detector calibration, weak lensing, peculiar velocities, and host-galaxy catalog completeness, and corresponding potential mitigation strategies, which currently limit the constraint precision of cosmological parameters. Looking forward, we highlight the importance of combining GW standard sirens with other emerging late-universe cosmological probes such as fast radio bursts, 21 cm intensity mapping, and strong gravitational lensing to forge a precise cosmological probe for exploring the late universe. Finally, we introduce the challenges and the role of machine learning in searching for more signals, ensuring reliable parameter inferences, and accelerating the inference process for cosmological parameters.

We investigate the implications of neutron star observations for understanding the origin of nucleon mass using a framework that combines three complementary approaches: the equation of state based on parity doublet structure for hadronic matter below 2n₀, the Nambu-Jona-Lasinio (NJL) model for quark matter above 5n₀, and integral constraints to minimize the ambiguities at the intermediate density region. By systematically exploring parameter spaces and comparing theoretical predictions with recent observational constraints, we establish constraints on the chiral invariant mass. Our results suggest that more than half of the nucleon mass originates from sources beyond spontaneous chiral symmetry breaking, challenging conventional understanding of nucleon mass generation. These constraints arise solely from fundamental physical principles and observational data, independent of specific assumptions about the nature of the quark-hadron transition, providing insights into the microscopic origin of hadron masses within a framework that combines a parity-doublet hadronic model with an NJL quark model.

The detection of gravitational waves (GWs) has opened a new window to test the fundamental nature of gravity. We present constraints on the nonstandard propagation of GWs using the spectral siren method applied to binary black hole (BBH) mergers from the third Gravitational-Wave Transient Catalog (GWTC-3). The spectral siren method exploits the redshift distribution of BBHs to probe the cosmic expansion history and break degeneracies between cosmology and modified gravity effects. We focus on the friction term v in the nonstandard GW propagation equation, which characterizes the running of the Planck mass. Assuming the standard ΛCDM cosmology, we find (nu=-1.1_{-1.1}^{+3.9}, nu=0.5_{-2.6}^{+3.5}) and (nu=0.7_{-2.3}^{+3.1}) (median and 90% credible interval) for the Truncated, Power Law + Peak, and Broken Power Law mass models, respectively. These results improve upon previous constraints from the bright siren event GW170817 by an order of magnitude, owing to the higher redshifts of BBHs in GWTC-3, which reach up to z ∼ 1. Our result suggests that the propagation of GWs is consistent with the predictions of general relativity, placing limits on modified gravity theories that predict a time-varying Planck mass. As the sensitivity of GW detectors improves, the spectral siren method will provide a powerful tool for testing gravity on cosmological scales and probing the physics of the early Universe.