We introduce crystal polaritons, hybrid excitations formed when the collective excitations of a periodic quantum-emitter array strongly couple to the resonant Bloch modes of a metasurface. This realizes a cavity-QED platform in which periodic light and periodic matter are treated on the same footing, allowing strong collective light-matter coupling in an extended, lossy, and dispersive nanophotonic structure. To describe this regime, we develop a reciprocal-space few-mode quantization based on macroscopic quantum electrodynamics, which maps the metasurface resonances seen by the emitter array onto a cavity-QED Hamiltonian at each in-plane momentum. We show that both plasmonic surface-lattice resonances and dielectric bound states in the continuum can enter the strong-coupling regime with a single emitter per unit cell. As a consequence of the resonant nonlinearities of the resulting crystal polaritons, the platform enables quantum light generation with efficiencies orders of magnitude higher than those achieved in conventional nonlinear metasurfaces.

We show theoretically that weak quantum fluctuations induced by a nonsymmetric electromagnetic environment may lead to a quantized transconductance of a multiterminal quantum contact rather than to a blockade of transport in the contact. The result suggests the possibility to realize quantum Hall phenomenology without its common ingredients and/or a topological quantum state.

Light-induced sliding ferroelectricity in two-dimensional van der Waals materials enables polarization control via relative layer motion. However, polarization switching occurs on the timescale of shear modes (tens of picoseconds) and requires very large fluences, potentially damaging the samples. Here, using constrained density functional theory and many-body real-time simulations, we demonstrate an ultrafast electronic reversal of the total out-of-plane polarization sign in the photoexcited state, without requiring interlayer sliding, in rhombohedrally stacked transition metal dichalcogenide bilayers. The polarization changes sign relative to its initial ground-state value at moderate fluences and within $\sim 200\mathrm{fs}$, about 50 times faster than the typical shear-mode period. The ultrafast switching is driven by a rearrangement of localized dipoles around the tungsten sites and can be probed by phase-sensitive transient second-harmonic generation measurements. We establish a novel general mechanism for electronic control of low-dimensional ferroelectrics common to all polar multilayers having type II band alignment. Our Letter has direct implications for ultrahigh-speed volatile optical memory operating on subpicosecond timescales.

Motivated by recent progress in moiré superlattices and spin-$1/2$ triangular-lattice antiferromagnets, we study how orbital magnetic flux and Zeeman coupling compete or cooperate in generating internal U(1) gauge flux in a triangular spin liquid. We show that orbital flux favors a chiral spin liquid with staggered internal flux, whereas Zeeman coupling destabilizes the spinon Fermi-pocket state toward a Landau-level state with spontaneous uniform internal flux and conical spin order. We demonstrate this mechanism in a spin-$1/2$ $J_1\text{−}{J}_2\text{−}{J}_{\chi }$ model and further identify thermal Hall and magnetic signatures that distinguish these regimes, with potential applications to moiré Hofstadter-Hubbard systems and triangular-lattice antiferromagnets.

We study ultrafast magneto-photocurrents in a three-dimensional topological insulator. For this purpose, we excite ${({\text{In}}_r{\text{Bi}}_{1-r})}_2{\text{Se}}_3$ thin films with a femtosecond laser pulse in the presence of an external magnetic field ${\mathit{B}}_{\mathrm{ext}}$ up to $0.3\mathrm{T}$ parallel to the film plane. The resulting in-plane photocurrent is measured by detecting the emitted terahertz electromagnetic pulse. It is proportional and perpendicular to ${\mathit{B}}_{\mathrm{ext}}$. Strikingly, for $r\ge 4\%$, we observe an abrupt photocurrent reduction, which is strongly correlated with the indium-induced quenching of the topological surface states. The rise time, decay time, and amplitude of the terahertz magneto-photocurrent can consistently be explained by the following scenario: optically excited spin-polarized electrons propagate toward the film surface where the accumulated spin is converted into an in-plane charge current due to spin-velocity locking. Our results are highly relevant for contact-free probing of spin-charge conversion in systems without spontaneous magnetic order and without having to add invasive spin-source layers.

Hidden spin polarization (HSP), in which spin-polarized states exist locally while the total spin polarization is hidden in momentum space, has been extensively studied in nonmagnetic and collinear magnetic systems but remains largely unexplored in noncollinear magnets. Here we establish a unified symmetry framework for HSP in noncollinear magnetic materials based on spin-group theory. We show that spin symmetries systematically constrain nonrelativistic spin polarization, giving rise to four distinct split spin-texture (SST) types for each local sector, denoted as SST-1, SST-2, SST-3, and SST-4. Based on these splitting forms, together with the dimensionality of the associated local spin textures and the symmetry relations between different local sectors, we further classify HSP into three categories: HSP-1, HSP-2, and HSP-3. We illustrate these categories using tight-binding models and representative material examples, including ${\mathrm{SrFe}}_2{\mathrm{Se}}_2\mathrm{O}$, USb, ${\mathrm{Sr}}_2{\mathrm{Mn}}_3{\text{Sb}}_2{\mathrm{O}}_2$, PrFeAsO, and ${\mathrm{GdMn}}_2{\mathrm{Si}}_2$. A survey of the MAGNDATA database further identifies 133, 7, and 139 candidate noncollinear magnetic materials hosting HSP-1, HSP-2, and HSP-3, respectively. In addition, our symmetry analysis and first-principles calculation show that many of these materials can exhibit nonzero spin-related response tensors. These results establish a general framework for understanding HSP in noncollinear magnets and highlight their potential for spin-dependent functionalities.

We introduce many-body caging as a novel mechanism for nonthermal behavior in quantum matter. We define many-body cages as eigenstates that, through quantum interference, become localized on a subgraph of the many-body state graph. These many-body cages can lead to the formation of flat bands in the many-body spectrum at characteristic, system-independent energies. These flat bands can realize a novel type of glassy eigenspectrum order in the absence of disorder, which we quantify by a band-overlap order parameter with an intricate, possibly fractal, distribution over the many-body state graph. We further show that these many-body cages exhibit distinctive signatures in experimentally accessible quantities, such as through a nonvanishing long-time memory of the initial condition, and many-body Rabi oscillations set by the characteristic flat-band energies. While our predictions in principle apply to any constrained quantum system, we demonstrate them here for 2D lattice gauge theories and models relevant for current experiments in Rydberg atoms. We expect that these many-body cages offer a promising route to realize nonequilibrium quantum states with novel properties.

The emergence of the $r=0$ singularity inside a spherically symmetric charged black hole is studied numerically within the Einstein-Maxwell-real scalar model. When the scalar field reaches a critical strength, the $r=0$ singularity emerges inside the black hole at the tip of the causal diamond. By varying the parameter $p$ of the initial profile for the scalar field toward the critical value $p_{*}$, we observe the areal radius at the tip follows a power-law scaling, $r_S\propto |p-p_{*}{|}^{\gamma }$, with a universal critical exponent $\gamma \approx 0.5$. This remarkable discovery, analogous to Choptuik’s critical phenomena for the black hole formation, provides the first evidence of the universality and scaling for the emergence of the $r=0$ singularity inside spherically symmetric charged black holes, offering new insights into the nonlinear dynamics of strong gravitational fields.

Critical metrology relies on the high sensitivity of systems to parameter changes near a phase transition to extract information with high precision. Such methods usually require working under adiabatic conditions, which implies long preparation times due to critical slowing down. Here instead we demonstrate how favorable sensitivity can be maintained for preparation rates exceeding the adiabatic limit by exploiting knowledge of the nonequilibrium dynamics of the system. Our work focuses on a model of collective dissipation (superradiance) balanced by collective pumping, analyzing the sensitivity around a first order dissipative phase transition. We devise a sensing protocol based on characterizing the hysteresis formed beyond adiabatic conditions, finding the sensing uncertainty $r^{\alpha }/N$, exhibiting a favorable Heisenberg-like scaling with the particle number $N$ and only a weak power-law dependence $\alpha \approx 0.17$ on the preparation rate $r$. We discuss the implementation of the model and potential applications to metrology within cavity QED setups.

We propose a transient vector quantum magnetometry protocol based on cavity-magnon systems. By exploiting finite-time dynamics initialized from a reservoir-engineered squeezed steady state, our scheme retains residual squeezing-induced quadrature noise reduction, which suppresses transient added noise and enhances the short-time signal-to-noise ratio beyond conventional unsqueezed steady-state limits. IQ demodulation of orthogonal cavity-output quadratures enables crosstalk-free reconstruction of all three components of a transient magnetic field, providing access to both its magnitude and orientation. This vector capability is relevant for short-lived magnetic phenomena such as pulsed spin excitations, magnetic textures, nanoscale current transients, and biomagnetic signals. In the long-time limit, we derive a closed-form stationary noise spectrum and identify the on-resonance noise-cancellation condition $g_{am}=\sqrt{{\kappa }_a{\kappa }_m}/2$ at which the cavity-added noise vanishes without strong coherent coupling. Injected squeezing further suppresses the cavity-added noise away from resonance, while an array of $N$ yttrium iron garnet spheres reduces the magnon-probe noise contribution by a factor of $1/N$. Our results establish cavity-magnon systems as a scalable platform for transient, vector-resolved quantum magnetometry.

We show that an isotropic medium with broken inversion symmetry can exhibit spin-1 Weyl points with a charge of 2. Such points are protected by SO(3) rotational symmetry (isotropy). We study such points in three different systems: a homogeneous chiral Lorentz medium, a periodic chiral metamaterial with point group symmetry, and a random chiral metamaterial with statistical isotropy. We further discuss how such points can be observed through reflectance and transmittance spectra. Our results demonstrate that nontrivial topology can be obtained in isotropic metamaterials, including self-assembled systems.

Dislocation motion, as a fundamental phenomenon modulating the microstructures of solid crystals, substantially affects material properties. Normally, dislocation motion is activated due to the presence of mechanical factors. But for nonmetals, nonmechanical factors like electronic stimulus have increasingly attracted interest in their potential for manipulating dislocation behavior. In this Letter, we report a forward-and-backward local core motion manner of a mixed-type partial dislocation in semiconductor aluminum nitride triggered by electron beam radiation. Such a motion behavior is beyond conventional understanding from the mechanical perspective but can be rationalized by a Fermi-level-dominated mechanism. Crystallographic analysis reveals that this local core motion is implemented by the vacancy-assisted climb of the edge component coupled with the glide of the screw component. First-principles calculations suggest that radiation-induced Fermi-level reduction modifies the charge state of dislocation cores and vacancies. Consequently, the partial dislocation core can locally move via absorbing or releasing charged vacancies to reach a lower-energy charge state. This mechanism was validated under varying irradiation conditions and is applicable to gallium nitride with a smaller band gap. Our findings identify Fermi levels as a nonmechanical stimulus of local dislocation-core motion and enrich the possible methods for dislocation manipulation in semiconductors.

Magnons with momentum-dependent chirality are a key signature of altermagnets. We identify bicircular light as a smoking-gun optical probe for chiral altermagnetic magnons, selectively targeting their quantum geometry induced by an alternation of magnonic chirality. We show that in $d$-wave altermagnets, under a canting magnetic field, the altermagnetic magnons realize a nontrivial quantum geometry, resulting in an enhancement of the nonlinear second-order light-magnon interactions. We find that the scattering of bicircular pulses probes the present magnonic quantum geometry, even if the magnonic topology is trivial. Hence, our findings establish bicircular Raman response as an optical effect of choice to identify altermagnetic magnons. As such, we propose a universal experimental protocol to distinguish altermagnets from antiferromagnets by detecting their magnon chirality patterns with light, independently of the underlying magnon topology.

Multipartite entanglement is a key resource for quantum technologies, yet its certification typically relies on correlations from measurements involving all particles, making it increasingly vulnerable to imperfections as the system size grows. Here we report the first experimental demonstration of genuine multipartite entanglement detection from correlations with the minimum possible nontrivial support, known as the entanglement detection length (EDL). Using a photonic platform, we certify W, Dicke, and cluster states with entanglement witnesses constructed from correlations at the EDL. In particular, we verify genuine multipartite entanglement of three- and four-qubit W states and a four-qubit Dicke state using two-body correlations, and of a four-qubit cluster state using three-body correlations. For the four-photon Dicke state, we further show that this minimal-correlation strategy is more robust than the compared global witness under the analyzed local-basis-misalignment model. We also find that, within the witness families considered here, increasing the number of measured subsets enhances the tolerance to noise. These results establish entanglement detection at the EDL limit as a measurement-efficient route to multipartite entanglement certification.