Reports on progress in physics. Physical Society (Great Britain)最新文献

We introduce entropic measures to quantify non-classical resource in hybrid spin-boson systems. We discuss the stabilizer Renyi entropy in the framework of phase space quantisation and define an analogous hybrid magic entropy and a mutual magic entropy that capture the distribution of quantum magic across spin and bosonic subsystems. We use these entropic measures to demonstrate two key phenomena: the detection of the superradiant phase transition in the Dicke model and the quantum dynamics of magic in the Jaynes-Cummings model. We develop a Monte Carlo numerical scheme to practically evaluate these entropic measures in interacting many-body systems.

We report precision, orbital-resolved measurements of three-body recombination near the 159 Gp-wave Feshbach resonance in an ultracold gas of⁶Li atoms prepared in their lowest hyperfine state. Using a radio-frequency gated protocol that suppresses magnetic-field transients below the milligauss level, we resolve loss features associated with the |m_ℓ|=1 and m_ℓ=0 orbital projections. The measured three-body loss coefficient L₃is well captured by a thermally averaged cascade-recombination model, enabling extraction of the resonance splitting δB and effective-range parameter k_e. At the lowest temperature, we obtain δB = 7.6(3) mG and k_e= 0.151(6) a₀^-1, both in quantitative agreement with coupled-channel theory. These results establish orbital-resolved three-body spectroscopy as a precision probe ofp-wave scattering and provide a benchmark for microscopic models of resonant few-body loss.

Fermi arcs in Weyl semimetals provide a unique platform for surface-state engineering, yet directly tracking of their evolution under surface tuning remains experimentally challenging. Here we theoretically propose that nonreciprocal charge transport can serve as a direct probe of Fermi arc Lifshitz transitions (FALT). We show that different surface terminations in Co3Sn2S2 can produce finite and highly tunable second-order nonreciprocal signals, which can be further modulated by adjusting the surface potential. Strikingly, we show that the second-order conductivity exhibits sign changes as the Fermi arc connectivity is tuned across FALT driven by gating or chemical potential variation. This behavior arises from the chiral nature of electron velocities on the Fermi arcs, and is highly sensitive to surface termination and symmetry breaking. Our findings establish nonreciprocal transport as an electrically measurable fingerprint of FALT and propose new strategies that could be directly applied in devices for in situ engineering and detecting transport properties in topological materials.

For over three decades, the study of optical vortex beams carrying orbital angular momentum has been at the forefront of optics, driven by fundamental questions about optical momentum as well as diverse applications in quantum information, communications, and optical manipulation. Most work has focused on paraxial beams, whose transverse fields are accurately described by conventional wave optics and the Stokes formalism. By contrast, when light is confined to the nanoscale and tightly focused beyond the paraxial regime, vortex beams exhibit complex electromagnetic structures that transcend these conventional models. In this deeply non-paraxial regime, the resulting fields display rich and often counterintuitive behavior, opening new perspectives on light-matter interactions. This review unifies the emerging physics of nanoscale optical vortices by developing a coherent theoretical framework and offering a critical synthesis of recent advances, guiding readers toward a deeper understanding and stimulating future work in this rapidly evolving field.

In solution, electrically like-charged particles can experience a strong and long-ranged attraction that leads to the formation of stable, slowly reorganizing clusters. The attractive force underpinning this spontaneous organization process has been shown to depend on both the sign of charge of the particle and the nature of the solvent medium. The origin of the attraction has been ascribed to the preferential orientation of solvent molecules at the object-electrolyte interface. Here, we use optical imaging to directly measure the spatial profile of the potential of mean force between isolated pairs of charged microspheres. Working with particles carrying a variety of surface chemistries we find that the range of the electrosolvation attraction is substantially longer than previously held. In particular we show that particles carrying strongly anionic surface coatings composed of DNA or phospholipid bilayers display long-range attraction. We further find that the length scale governing the decay of the attractive force can depend on the properties of the interacting particles. This contrasts with the canonical expectation that the screening length governing the interaction of charged particles in solution depends exclusively on the properties of the intervening electrolyte medium. The observations point to significant departures from current thinking, and the likely need for a model of interactions that accounts for the molecular nature of the solvent, its interfacial behaviour, and spatial correlations. Finally, a strong and long-ranged attraction mediated by anionic matter constituting lipid membranes and chromatin could carry far-reaching implications for biological organization and structure formation.

Diffusive motion is a fundamental transport mechanism in physical and biological systems, governing dynamics across a wide range of scales-from molecular transport to animal foraging. In many complex systems, however, diffusion deviates from classical Brownian behaviour, exhibiting striking phenomena such as Brownian yet non-Gaussian diffusion (BYNGD) and anomalous diffusion. BYNGD describes a frequently observed statistical feature characterised by the coexistence of linear mean-square displacement (MSD) and non-Gaussian displacement distributions. Anomalous diffusion, in contrast, involves a nonlinear time dependence of the MSD and often reflects mechanisms such as trapping, viscoelasticity, heterogeneity, or active processes. Both phenomena challenge the conventional framework based on constant diffusivity and Gaussian statistics. This review focuses on the theoretical modelling of such behaviour via the Langevin equation with fluctuating diffusivity (LEFD)-a flexible stochastic framework that captures essential features of diffusion in heterogeneous media. LEFD not only accounts for BYNGD but also naturally encompasses a wide range of anomalous transport phenomena, including subdiffusion, ageing, and weak ergodicity breaking. Ergodicity is discussed in terms of the correspondence between time and ensemble averages, as well as the trajectory-to-trajectory variability of time-averaged observables. The review further highlights the empirical relevance of LEFD and related models in explaining diverse experimental observations and underscores their value to uncovering the physical mechanisms governing transport in complex systems.

We demonstrate the existence of doubly charged exciton states in strongly screened bilayers of transition metal dichalcogenide layers. These complexes are important because they are preformed electron pairs that can, in principle, undergo Bose-Einstein condensation, in which case they would also form a new type of superconductor, consisting of stable bosons with net charge. Our measurements include 1) continuous control of the doping density with both positive and negative carriers, showing the expected population dependencies on the free carrier density, and 2) measurement of the dependence on magnetic field, showing that this new bound state is a spin triplet. These results imply that it is promising to look for superconductivity in this system.

Self-propulsion is a quintessential aspect of biological systems, which can induce nonequilibrium phenomena that have no counterparts in passive systems. Motivated by biophysical interest together with recent advances in experimental techniques, active matter has been a rapidly developing field in physics. Meanwhile, over the past few decades, topology has played a crucial role to understand certain robust properties appearing in condensed matter systems. For instance, the nontrivial topology of band structures leads to the notion of topological insulators, where one can find robust gapless edge modes protected by the bulk band topology. We here review recent progress in an interdisciplinary area of research at the intersection of these two fields. Specifically, we give brief introductions to active matter and band topology in Hermitian systems, and then explain how the notion of band topology can be extended to nonequilibrium (and thus non-Hermitian) systems including active matter. We review recent studies that have demonstrated the intimate connections between active matter and topological materials, where exotic topological phenomena that are unfeasible in passive systems have been found. A possible extension of the band topology to nonlinear systems is also briefly discussed. Active matter can thus provide an ideal playground to explore topological phenomena in qualitatively new realms beyond conservative linear systems.

The thermoelectric performance of a material is determined by the fundamental transport dynamics of itinerant charge carriers and their interactions with the environment. For two-dimensional oxide thermoelectrics, predominantly represented by doped SrTiO₃-based superlattices (SLs), reduced spatial dimensions and increased effective mass are known to enhance thermopower (S). However, because of their large effective Bohr radius resulting from the high dielectric constant, SrTiO₃-based systems have limitations in exhibiting the 2D characteristic. Here, we focus on EuTiO₃as an alternative perovskite platform in which fractional La_xEu_1-xTiO₃/EuTiO₃artificial SLs demonstrate the improvement in 2D nature for the dimensionality-induced enhancement ofS. We observed a quasi-2D thermopowerS_2Dof -950μV K^-1andS_2D/S_3Dof ∼20 resulting from the improved 2D confinement. Thermopower measurements, combined with hybrid density functional theory calculations, show the enhancedSoriginates from the confinement of Ti 3d_xy-orbitals within the La_xEu_1-xTiO₃layers and the associated increase in the 2D density of states. A smaller effective Bohr radius and modified electronic band structures, in conjunction with the presence of the Eu 4f-states in EuTiO₃modified the local electronic potential and strengthened the spatial confinement of Ti 3d-states. This approach to improving the dimensional confinement establishes a small effective Bohr radius and 4f-state assisted 2D confinement provides valuable insights into the design of high-performance applications in artificial oxide SLs.

Frequency metrology is a cornerstone of modern precision measurements and optical atomic clocks have emerged as one of the most precise measurement devices. In this progress report, we explore various Ramsey interrogation schemes tailored to optical atomic clocks primarily limited by laser noise. To incorporate frequency fluctuations directly into the theoretical model, we consider a Bayesian framework. In this context, we review fundamental bounds arising in Bayesian estimation theory, which serve as a benchmark throughout this work. We investigate the trade-off between entanglement-enhanced sensitivity and robustness against laser noise in order to identify optimal initial states, measurement schemes and estimation strategies. Beside standard protocols based on coherent spin states, spin-squeezed states and Greenberger-Horne-Zeilinger states, we consider variational Ramsey protocols implemented via low-depth quantum circuits based on one-axis twisting operations to approach optimal stability. In particular, we review known and identify new optimal Ramsey interrogation schemes for a variety of scenarios, including different experimental platforms, ensemble sizes and regimes characterized by a wide range of interrogation durations and dead times. Hence, this work establishes a comprehensive theoretical framework for optimizing Ramsey interrogation schemes, providing guidance for the development of next-generation optical atomic clocks.