Communications Physics最新文献

Spontaneous symmetry breaking (SSB) plays a central role in many areas of physics, from particle interactions to optical systems. Exceptional points (EPs), where system properties become degenerate, are often believed to occur together with SSB. Here we investigate the intricate relationship between SSB and a specific class of EPs across three distinct, real-world scenarios in nonlinear optics. In these systems, the two phenomena do not coincide; they occur at dislocated points in parameter space, but are interdependent. This recurring behavior across disparate platforms implies that such decoupling is not unique to these optical systems, but likely reflects a more general principle. Our results highlight the need for careful analysis of assumed correlations between SSB and EPs in both theoretical and applied contexts. They deepen our understanding of nonlinear dynamics in optical systems and prompt a broader reconsideration of contexts where EPs and SSB are thought to be interdependent.

Many real-world systems exhibit higher-order interactions beyond pairwise links. Such interactions are modeled by undirected hypergraphs where edges can connect any number of vertices, but without capturing the directional nature of many real-world interactions. Directed hypergraphs overcome this limitation by distinguishing source and target sets within each hyperedge, enabling analysis of directional information flow. Here, we provide a framework to characterize the structural organization of directed higher-order networks at their microscale. We extract the fingerprint of a directed hypergraph, capturing the frequency of hyperedges with a certain source and target sizes, and use this information to compute differences in higher-order connectivity patterns among real-world systems. Then, we investigate the overlap among sources and targets to reveal recurring sets of co-sending and co-receiving nodes. We define reciprocity in hypergraphs using exact, strong, and weak definitions to quantify the extent to which hyperedges are reciprocated. Finally, we extend motif analysis to identify recurring interaction patterns and extract the building blocks of directed hypergraphs. We validate our framework on empirical datasets, including Bitcoin transactions, metabolic networks, and citation data, revealing structural principles behind the organization of real-world systems.

Phase-retrieval from coded diffraction patterns (CDP) is important to X-ray crystallography, diffraction tomography and astronomical imaging, yet remains a hard, non-convex inverse problem. We show that CDP recovery can be reformulated exactly as the minimization of a continuous-variable XY Hamiltonian and solved by gain-based photonic networks. The coupled-mode equations we exploit are the natural mean-field dynamics of exciton-polariton condensate lattices, coupled-laser arrays and driven photon Bose-Einstein condensates, while other hardware such as the spatial photonic Ising machine can implement the same update rule through high-speed digital feedback, preserving full optical parallelism. Numerical experiments on images, two- and three-dimensional vortices and unstructured complex data demonstrate that the gain-based solver consistently outperforms the state-of-the-art Relaxed-Reflect-Reflect (RRR) algorithm in the medium-noise regime (signal-to-noise ratios 10-40 dB) and retains this advantage as problem size scales. Because the physical platform performs the continuous optimisation, our approach promises fast, energy-efficient phase retrieval on readily available photonic hardware.

Stability analysis of two-fluid protoplanetary disc models has enriched our understanding of how solids can grow into larger bodies called planetesimals. Dust particles entrained in a gas stream modify the flow, creating shear layers prone to instability. In such environments, drag occurs in the free-molecular (Epstein) regime. Recreating these two-phase flows on Earth is difficult due to gravity-driven buoyancy. Here, we use particle image velocimetry to study a low-pressure dust-gas mixture at Knudsen numbers up to 10 in microgravity. We observe a granular shear flow instability, characterized by a periodic velocity field, which can be modeled to first order as a Kelvin-Helmholtz (KH) instability. This behavior resembles a Kelvin-Helmholtz instability and provides a benchmark for two-fluid theories relevant to planet formation.

Probing the possibility of entanglement generation through gravity offers a path to tackle the question of whether gravitational fields possess a quantum mechanical nature. A potential realization necessitates systems with low-frequency dynamics at an optimal mass scale, for which the microgram-to-milligram range is a strong contender. Here, after refining a figure-of-merit for the problem, we present a 1-milligram torsional pendulum operating at 18 Hz. We demonstrate laser cooling its motion from room temperature to 240 microkelvins, surpassing by over 20-fold the coldest motions attained for oscillators ranging from micrograms to kilograms. We quantify and contrast the utility of the current approach with other platforms. The achieved performance and large improvement potential highlight milligram-scale torsional pendulums as a powerful platform for precision measurements relevant to future studies at the quantum-gravity interface.

Spin-orbit torques (SOTs) are essential for electrically controlling magnetic order in spintronic devices. Platinum (Pt) is ubiquitous for SOT generation due to its strong bulk spin Hall and interfacial Rashba-Edelstein effects. Here, we revisit this established viewpoint by investigating ultrathin Pt films interfaced with a typical magnetic insulator, terbium iron garnet. We find that few-atom-thick, nanogranular Pt exhibits exceptionally efficient SOT-induced switching that cannot be explained by these conventional mechanisms. This enhancement is attributed to the granular morphology of sputtered Pt, which activates two complementary mechanisms: enhanced spin-orbit scattering at grain boundaries, leading to an increased effective spin Hall angle, and localized current density amplification due to non-uniform conduction paths. Furthermore, adding a titanium (Ti) or manganese (Mn) overlayer to thin Pt enhances the switching efficiency, indicating an active contribution from light metals via orbital current generation. These findings uncover key SOT pathways in ultrathin heterostructures and provide insights for optimizing spin-orbitronic device performance and enabling energy-efficient magnetic switching.

Lattice gauge theory is an important framework for studying gauge theories that arise in the Standard Model and condensed matter physics. Yet many systems (or regimes of those systems) are difficult to study using conventional techniques, such as action-based Monte Carlo sampling. In this paper, we demonstrate the use of gauged Gaussian projected entangled pair states as an ansatz for a lattice gauge theory involving dynamical physical matter. We study a $Z_2$ gauge theory on a two dimensional lattice with a single flavor of fermionic matter on each lattice site. For small systems, our results show agreement with results computed by exactly diagonalizing the Hamiltonian, and demonstrate that the approach is computationally feasible for larger system sizes where exact results are unavailable. This is a further step on the road to studying higher dimensions and other gauge groups with manageable computational costs while avoiding the sign problem.

The experimental discovery of fractional Chern insulators (FCIs) in moiré materials raises the question of whether their time-reversal invariant analogs, fractional topological insulators (FTIs), can also be realized in these platforms. We address this via exact diagonalization calculations in both a Landau level (LL) model and continuum model for twisted MoTe₂, and extract principles for engineering FTIs in realistic conditions. For the spinful LL model at filling $\nu =\frac{1}{3}+\frac{1}{3}$ , we show that a suppression of the short-range component of the interaction is important to stabilize the FTI. For twisted MoTe₂ at $\nu =-\frac{4}{3}$ , we find that a short-range attraction g on top of the screened Coulomb interaction is needed to realize an FTI. We discuss how this threshold value of g could be reduced by examining larger system sizes, incorporating band-mixing effects, exploiting Landau level character, and engineering the dielectric environment. While our study highlights the challenges, at least for the fillings considered, for obtaining FTIs, we also provide potential sample-engineering routes to improve the stability of FTI phases.

Photonic ultrasound sensors promise unparalleled spatial and temporal resolution in ultrasound imaging due to their size-independent noise figure, high sensitivity, and broad bandwidth. Optical materials can further improve performance and stability, but achieving small size, high sensitivity, and wide bandwidth remains challenging. This work introduces amorphous silicon carbide (a-SiC) for ultrasound sensing, offering strong optical confinement, low propagation loss, and high stability for miniaturized microring sensors. We demonstrate a compact detection system with a 20-transducers linear array coupled to a single bus waveguide. The sensors achieve an optical finesse of 1320 and intrinsic sensitivity of 78 fm kPa^-1, leading to a noise-equivalent pressure below 55 $\mathrm{mPa}/\sqrt{\mathrm{Hz}}$ , calibrated from 3.36 MHz to 30 MHz. High-resolution imaging of fine structures validates real-world applicability. a-SiC is also easily integrated on most substrates due to its low deposition temperature. Our results position a-SiC as a promising solution for optical ultrasound sensing, combining miniaturization, low-loss, and high-sensitivity.

Quantum computers promise to simulate complex quantum field theories that are intractable for classical computers, potentially revealing new physics in strongly interacting systems. Current approaches for simulating Yang-Mills gauge theories face significant technical barriers due to complex group structures and complicated truncation schemes that vary drastically between different theories. Here we show that the orbifold lattice formulation provides a universal framework for quantum simulation of Yang-Mills theories with arbitrary gauge groups and dimensions. Our approach reduces all theories to the same simple Hamiltonian form, enabling implementation with standard quantum gates regardless of system complexity. We demonstrate explicit quantum circuits using only controlled-NOT and single-qubit operations, with concrete resource estimates for time evolution algorithms. This universal framework simplifies quantum simulation of gauge theories and enables systematic scaling to larger systems on fault-tolerant quantum computers.