We investigate the occurrence of genuine quantum effects and beyond mean-field physics in the balanced and unbalanced open Dicke models with a large yet finite number of atoms $N$. Such driven and dissipative quantum many-body systems have recently been realized in experiments involving ultracold gases inside optical cavities and are known to obey mean-field predictions in the thermodynamic limit $N\to \infty$. Here we show quantum effects that survive for large but finite $N$, by employing a novel open-system dynamics method that allows us to obtain numerically exact quantum dynamical results for atom numbers up to a mesoscopic $N\approx 1000$. While we find that beyond-mean-field effects vanish quickly with increasing $N$ in the balanced Dicke model, we are able to identify parameter regimes in the unbalanced Dicke model that allow genuine quantum effects to persist even for mesoscopic $N$. They manifest themselves in a strong squeezing of the steady state and a modification of the steady-state phase diagram that cannot be seen in a mean-field description. This is due to the fact that the steady-state limit $t\to \infty$ and thermodynamic limit $N\to \infty$ do not commute.

The concepts of twistronics and magic angle have been widely applied beyond electrons, powering up new advancements in optics, acoustics, and heat transport. However, achieving a unidirectional or all-direction “magic angle” remains an established yet unresolved challenge in twisted bilayer metasurfaces across various disciplines. Our work proposes and validates a “twist-on-twist” paradigm to realizing unidirectional propagation and robust magic angle at arbitrary directions of the elastic out-of-plane wave. Our elastic metasurface not only exhibits a twisted configuration between the stacked bilayer but also significantly enhances out-of-plane symmetry breaking by further twisting meta-atoms in one constituent layer. Our twist-on-twist method unleashes versatile potentials of twisted thin composite materials to control the extreme propagation of topological elastic waves and even opens up new possibilities for photonic, phononic, and thermal moiré metamaterials.

Living materials adapt their shape to signals from the environment, yet the impact of shape changes on signal processing and associated feedback dynamics remains unclear. We find that droplets with signal-responsive interfacial tensions exhibit shape bistability, excitable dynamics, and oscillations. The underlying critical points reveal novel mechanisms for physical signal processing through shape adaptation in soft active materials. We recover signatures of one such critical point in experimental data from zebrafish embryos, where it supports boundary formation.

Superconducting circuits comprising Josephson junctions have spurred significant research activity due to their promise to realize scalable quantum computers. Effective Hamiltonians for these systems have traditionally been derived assuming the junction connects superconducting islands of infinite size. We derive a quantized Hamiltonian for a Josephson junction between finite-sized islands and predict measurable corrections to the qubit frequency and charge susceptibility to test the theory.

When placing an ultracold atomic gas inside a cavity, the light-matter coupling is enhanced and nonlinear atomic dynamics is generated, offering a promising platform for quantum simulation of models with short- and long-range interactions. Recently, superradiant self-organized phases for ultracold atomic gases inside a cavity, pumped by a blue detuned optical lattice, have been observed. Here, we explore the formation of quantum many-body phases of bosonic atoms inside an optical cavity, subject to transverse blue detuned pumping. We investigate the strongly interacting regime, which can be reached by tuning the $s$-wave scattering length using external fields. We analyze the interplay between superradiant self-organization with superfluid and Mott insulator phases, without the need of including higher lying bands, as the Wannier functions are dynamically linked to the cavity light via backaction. We observe different kinds of structural phase transitions driven by the light inside the cavity and the interplay with atomic collisions. We observe the mode softening at the critical points in the quantum phase transitions which can be measured in future experiments. We obtain our results within a full self-consistent theoretical framework, the light-matter density matrix renormalization group (DMRG), which employs the computation of light dependent Wannier functions for the full quantum optical lattice in combination with DMRG for the atomic dynamics. The methods introduced here can be used to analyze the effects of strong quantum correlations in strongly interacting light-matter systems.

We identify regimes where postselection can be used scalably in quantum error correction (QEC) to improve performance. We use statistical mechanical models to analytically quantify the performance and thresholds of postselected QEC, with a focus on the surface code. Based on the nonequilibrium magnetization of these models, we identify a simple heuristic technique for postselection that determines whether to abort without requiring a decoder. Along with performance gains, this heuristic allows us to derive analytic expressions for postselected conditional logical thresholds and abort thresholds of surface codes. We find that such postselected QEC is characterized by four distinct thermodynamic phases and detail the implications of this phase space for practical, scalable quantum computation.

Solving linear ordinary differential equations (ODEs) is one of the most promising applications for quantum computers to demonstrate exponential advantages. The challenge of designing a quantum ODE algorithm is how to embed nonunitary dynamics into intrinsically unitary quantum circuits. In this Letter, we propose a new quantum algorithm for solving ODEs by harnessing open quantum systems. Specifically, we propose a novel technique called nondiagonal density matrix encoding, which leverages the inherent nonunitary dynamics of Lindbladians to encode general linear ODEs into the nondiagonal blocks of density matrices. This framework enables us to design quantum algorithms with both theoretical simplicity and high performance. Combined with the state-of-the-art quantum Lindbladian simulation algorithms, our algorithm can outperform all existing quantum ODE algorithms and achieve near-optimal dependence on all parameters under a plausible input model. We also give applications of our algorithm including the Gibbs state preparations and the partition function estimations.

The ground-state cooling and quantum control of levitated nanoparticles have become attainable, which makes the enhanced quantum sensing based on the large mass advantage of mesoscopic quantum systems accessible. Here, we propose an enhanced gravity-sensing protocol for a nanodiamond levitated in a linear ion trap, which improves the sensing sensitivity and further reduces device size. By introducing gravitational acceleration into the vibrational state through transient free fall, we achieve a square-accelerated relative phase accumulation, yielding higher sensitivity than the linear accumulation process. The sensitivity reaches the standard quantum limit for a nanodiamond containing multiple nitrogen-vacancy (N-V) centers. Besides, by using phonon-mediated one-axis twisting dynamics induced by magnetic field gradient to squeeze the initial spin state, the sensitivity can further surpass the standard quantum limit as a scaling law of $N^{-5/6}$. To fully assess the protocol performance, we further analyze the effects of decoherence and control errors, which are negligible under experimentally achievable conditions. Specifically, the sensitivity reaches $\sim 18\mathrm{\mu }\mathrm{Gal}/\sqrt{\mathrm{Hz}}$ for the nanodiamond containing only one N-V center over a free-fall distance of $\sim 20\mathrm{\mu }\mathrm{m}$, while exceeds $0.4\mathrm{\mu }\mathrm{Gal}/\sqrt{\mathrm{Hz}}$ for 100 N-V centers. Our results will further facilitate research on compact and high-sensitivity gravimeters.

We develop a nonperturbative definition of ${\mathrm{RMT}}_2$: a generalization of random matrix theory that is compatible with the symmetries of two-dimensional conformal field theory. Given any random matrix ensemble, its $n$-point spectral correlations admit a prescribed modular-invariant lift to ${\mathrm{RMT}}_2$, which moreover reduce to the original random matrix correlators in a near-extremal limit. Central to the prescription is a presentation of random matrix theory in Mellin space, which lifts to two dimensions via the $\mathrm{SL}(2,\mathbb{Z})$ spectral decomposition employed in previous work. As a demonstration we perform the explicit ${\mathrm{RMT}}_2$ lift of two-point correlations of the GUE Airy model. We propose that in ${\mathrm{AdS}}_3$ pure gravity, semiclassical amplitudes for off-shell $n$-boundary torus wormholes with topology ${\mathrm{\Sigma }}_{0,n}\times S^1$ are given by the ${\mathrm{RMT}}_2$ lift of JT gravity wormhole amplitudes. For the three-boundary case, we identify a gravity calculation which matches the ${\mathrm{RMT}}_2$ result.

We find a design principle for tailoring thermal expansion properties in nearly spherical molecular networks. Using 2D fullerene networks as a representative system, we realize positive thermal expansion along intermolecular [$2+2$] cycloaddition bonds and negative thermal expansion along intermolecular C-C single bonds by varying the structural frameworks of molecules. The microscopic mechanism originates from a combination of the framework’s geometric flexibility and its transverse vibrational characteristics. Based on this insight, we find molecular networks beyond ${\mathrm{C}}_{60}$ with tunable thermal expansion. These findings shed light on the fundamental mechanisms governing thermal expansion in molecular networks towards rational materials design.

Charged defect scattering of electrons plays a critical role in determining a wide range of material properties. However, there is a lack of an accurate method to calculate the scattering, as all the existing methods require assuming a specific distribution for unscreened (i.e., bare) excess charge carried by the defect, which limits their accuracy. Here we develop a first-principles method to determine the bare charge distribution, which thus enables accurate calculations of the scattering. Using this method, we accurately calculate the electron mobility of 2D ${\mathrm{MoS}}_2$ under the scattering of charged sulfur vacancies and compare with that of charge-neutral oxygen substitutes of sulfur. Interestingly, we find that the charged defect-limited mobility exhibits a strong temperature dependence at low temperature and carrier concentration, in contrast to the neutral defect and the conventional belief that the defect-limited mobility is less sensitive to the temperature. This behavior arises from the free carrier screening of the long-range scattering potential of the charged defect. Our work offers new insights into the transport mechanism, and opens access to accurate calculation, understanding, and prediction of charged defect scattering and a broad range of associated properties.

We reveal a hidden electrodynamical structure emerging from a general $2\times 2$ pseudo-Hermitian system that exhibits real spectra. Even when the Hamiltonian does not explicitly depend on time, the Berry curvature can be mapped onto a $2+1$-dimensional electromagnetic field arising from an artificial spacetime instanton, in sharp contrast to the Hermitian systems where the Berry curvature is equivalent to the static magnetic field of a magnetic monopole in three spatial dimensions. The instanton appearing as a spacetime singularity carries a topological charge that quantizes the jump of magnetic flux of the Berry curvature at the time origin. Our findings are demonstrated in a simple example related to antiferromagnetic magnons.

The non-Hermitian skin effect, nonreciprocity-induced anomalous localization of an extensive number of eigenstates, represents a hallmark of non-Hermitian topological systems with no analogs in Hermitian systems. Despite its significance across various open classical and quantum systems, the influence of nonlinearity has remained largely unclear. Here, we reveal the Hopf bifurcation of the nonlinear skin effect as a critical phenomenon unique to nonlinear non-Hermitian systems. We demonstrate that nonlinearity destabilizes skin states and instead gives rise to the emergence of delocalized states associated with limit cycles in phase space. We also uncover the algebraically localized critical skin effect precisely at the Hopf bifurcation point. We illustrate this behavior in a nonlinear extension of the Hatano-Nelson model in both continuum and lattice. Our Letter shows a significant role of nonlinearity in the skin effect and uncovers rich phenomena arising from the interplay between non-Hermiticity and nonlinearity.

Electrical manipulation of antiferromagnetic (AFM) states, a cornerstone of AFM spintronics, is a great challenge, requiring novel material platforms. Here we report the full control over AFM states by voltage pulses in the insulating ${\text{Co}}_3{\mathrm{O}}_4$ spinel well below its Néel temperature. We show that the strong linear magnetoelectric effect is fully governed by the orientation of the Néel vector. As a unique feature of ${\text{Co}}_3{\mathrm{O}}_4$, the magnetoelectric energy can easily overcome the weak magnetocrystalline anisotropy; thus, the Néel vector can be manipulated on demand, either rotated smoothly or reversed suddenly, by combined electric and magnetic fields. We achieve the nonvolatile switching within a few tens of nanoseconds between time-reversed AFM states in macroscopic volumes by voltage pulses. These observations render quasicubic antiferromagnets, like ${\text{Co}}_3{\mathrm{O}}_4$, an ideal platform for the ultrafast (picosecond to nanosecond) manipulation of microscopic AFM domains and may pave the way for the realization of AFM spintronic devices.

Magnet-free, far-field infrared nonreciprocal thermal radiation has been reported using Weyl semimetals or spatiotemporal modulation nanostructures, but these methods face challenges like requiring extremely low temperatures or high modulation frequencies and have limited spectral or angular ranges. Here, we demonstrate far-field nonreciprocal thermal Fizeau drag radiation around asymmetric exceptional points (EPs) by drifting electrons in graphene sheets on dielectric periodic nanostructures. First, the generation and evolution mechanisms of symmetric scattering EP pairs have been unveiled in parameter spaces (i.e., $w-\theta$ space, $w$ and $\theta$ are filling ratio of gratings and incident angle respectively). The EP pairs are connected by bulk Fermi arc along the $\theta$ axis whose length can be tuned over the whole angular range by modifying dielectric optical index. Drifting electrons contribute to asymmetrically redistributing EPs with specific angular and spectral positions at low drifting velocities due to Fizeau drag effects. These nonreciprocal behaviors of EPs in angle space have been used to shape magnet-free infrared nonreciprocal emissivity and absorptivity with different numbers of resonant peaks, resulting in more than an order of magnitude increase in wavelength-integrated thermal nonreciprocity. The physics that underpins the synergy between nonreciprocity and EPs offers new insights into areas such as non-Hermitian physics, nonreciprocal optics, and nonreciprocal thermal photonics.

Interface-enhanced superconductivity in single-unit-cell FeSe on ${\mathrm{SrTiO}}_3$ has been extensively pursued recently. The interfacial electron-phonon coupling (EPC) is widely proposed to enhance pairing, yet to be directly verified. Herein, using ultrafast pump-probe spectroscopy, we discover a coherent 4.2 THz optical phonon mode that emerges only upon photoexcitation in FeTe/FeSe/${\mathrm{SrTiO}}_3$ or FeTe/${\mathrm{SrTiO}}_3$ heterostructures, but is absent in bare Nb-doped ${\mathrm{SrTiO}}_3$ under identical subgap pumping. Atomic-scale electron energy loss spectroscopy in scanning transmission electron microscopy identifies this mode as out-of-plane oxygen vibrations localized at double ${\mathrm{TiO}}_x$ terminated interface. Crucially, the phonon amplitude in FeTe/FeSe/${\mathrm{SrTiO}}_3$ is more than twice as large as that in FeTe/${\mathrm{SrTiO}}_3$, which can be attributed to higher electron doping that strengthens dipole moments penetrating the FeSe layer, thereby resulting in an enhanced interfacial EPC. Temperature-dependent dynamics further highlight the unique electronic nature of monolayer FeSe in sustaining this robust coupling. These findings provide direct evidence for dipole-mediated interfacial EPC as a critical mechanism of interfacial superconductivity in $\mathrm{FeSe}/{\text{SrTiO}}_3$.

Femtosecond lasers are routinely used for inducing local modification, including nanostructuring, and ultrafast laser spectroscopy in solids. However, these studies are often being performed separately making the unveiling of exciting physical properties of laser-fabricated materials out of reach. Here, we present an all-optical platform combining the fabrication of nano to micrometer size single-shot “femtosecond-laser-delamination” membranes or cavities of ferromagnetic thin films and multilayers together with their quasi in situ characterization using the Abbe-limited interferometric, ultrafast scanning photo-acoustic and magneto-plasmonic microscopies. Ferromagnetic nickel and iron cavities display high-Q acoustic resonances providing access to long-lived ultrahigh frequency coherent phonon modes in the above 100 GHz frequency range. Cavities in cobalt-gold bilayers allow for magnetically controlled surface plasmon resonance experiments in the Otto configuration, which is otherwise very difficult to implement experimentally. Quantitative experimental characterization of functional magnetic cavities, supported by the numerical modeling of all experimental data, opens an avenue to design and fabricate tunable nanoscaled femtosecond-laser-delamination architectures in thin films and multilayers.