We experimentally investigate the second-order quantum coherence function of a superradiant burst in a cascaded quantum system. We chirally (i.e., direction dependently) couple about 900 cesium atoms to the forward-propagating mode of an optical nanofiber. We then prepare the ensemble close to the maximally excited state, where the subsequent collective emission of a burst is known as superfluorescence. Here, we observe that second-order coherence emerges in the course of the decay. This is a clear signature of the underlying collective dynamics that is also at the origin of the superradiant burst itself. We furthermore study the dynamics of the second-order coherence function of the emission in relation to the initial average dipole moment of the ensemble. In addition, by investigating the correlation of early and late photon emission events, we obtain evidence for fundamental shot-to-shot fluctuations in the delay of the emission of the burst. Our findings thus reveal surprising similarities between superradiance in cascaded and symmetrically coupled systems, despite the fact that they are described by fundamentally different coupling Hamiltonians.

Soliton mode locking in microresonators enables chip-scale generation of low-noise optical and microwave signals. Pulse pumped solitons offer a platform for broadband microcomb generation with stabilized repetition rates and for exploring soliton physics. In this Letter, we present a theoretical and experimental investigation of Kerr-induced phase noise quenching (KINQ) in pulse pumped solitons. We derive a model that quantifies the locking bandwidth between the soliton and the pump pulse and reveals the mechanism of KINQ. Experiments in a silica microresonator show up to $\sim 20\mathrm{dB}$ of phase noise suppression from the pump. The lowest noise is achieved by tuning the pump repetition rate to expand the soliton existence range and operating near, but not at, its upper boundary of this range. Our results establish a theory for solitons trapped by a nonuniform background and offer guidelines for attaining low-noise states in coherently pumped systems.

Separate exact scaling laws are derived for the cascades of the kinetic and magnetic energy in incompressible homogeneous isotropic magnetohydrodynamic (MHD) turbulence, and validated by numerical simulations. The third-order moments exhibit linear scaling with respect to the spatial displacement scale in both the subviscous region and in the inertial range, and are proportional to the rate of conversion of kinetic energy to magnetic energy in the subviscous region, but to the energy injection rates in the inertial range, highlighting the impact of forcing mechanisms on energy transfer within MHD turbulence. Further analysis demonstrates that the Politano and Pouquet [Phys. Rev. E 57, R21 (1998).] $\frac{4}{5}$ law emerges as a specific case of our exact laws, when the antisymmetric flux term, closely associated with the nonlocal nature of energy transfer in MHD turbulence, is neglected, which is only valid in the absence of magnetic energy injection. These laws are of fundamental importance in MHD turbulence theory, and offer substantial potential to enhance the predictive capability to estimate the dissipation rates of the solar wind.

We report the first experimental observation of carrier-envelope phase-driven energy bunching in laser wakefield acceleration. Using a few-cycle ($\sim 9\mathrm{fs}$), multiterawatt laser pulse and ionization injection in a helium-nitrogen gas mixture, we observe electron spectra composed of multiple quasimonoenergetic peaks with regular narrow energy spacing. This comb structure arises from intermittent trapping from successive half-cycles of the laser field enabled by the evolving carrier-envelope phase during propagation in the plasma. These findings establish subcycle ionization injection as a potential route to attosecond control in plasma acceleration, enabling trapping and beam structuring synchronized to the optical waveform on subfemtosecond timescales.

The realization of robust quantum storage devices relies on the ability to generate long-lived, spatially localized states. In this Letter, we introduce a method for the targeted creation of compact excitations in flat-band lattices. By injecting in-plane radiation waves from the system’s edge and applying a localized on-site potential at the desired storage position, we induce hybridization between compact localized states of the flat band and resonant dispersive plane waves. This hybridization enables the formation of spatially compact, stable excitations suitable for quantum memory applications. We experimentally validate this mechanism using photonic waveguide arrays, focusing on two representative geometries: the diamond chain and the one-dimensional Lieb ladder. Our approach is broadly applicable to any platform supporting flat-band physics.

Altermagnetism, a recently discovered magnetic phase characterized by spin-split bands without net magnetization, has emerged as a promising platform for novel physics and potential applications. However, its stability against disorder—ubiquitous in real materials—remains poorly understood. Here, we study the electron localization properties of two-dimensional $d$-wave altermagnets subject to disorder. Remarkably, we discover a disorder-driven phase transition from a marginal metallic phase to an insulator, which falls into the Kosterlitz-Thouless class. We demonstrate this by strong numerical evidence and propose an interpretation in terms of vortex-antivortex pairs in the disorder-induced local in-plane spin magnetization. Moreover, we show that the characteristic spin anisotropy of altermagnets persists but gradually fades away across the transition. These changes directly affect the spin-splitting features that are detectable in angle-resolved photoemission spectroscopy and tunneling magnetoconductance. Our findings provide a new perspective on recent experimental observations of altermagnetism in candidate materials.

Ultrasensitive magnetometers based on spin resonances have led to remarkable achievements. However, the field responsivities of these spin resonances are inherently constrained by these particles’ gyromagnetic ratios, such as the electron, with a constant gyromagnetic ratio of ${\gamma }_e=2\pi \times 28\mathrm{GHz}/\mathrm{T}$. Here, we demonstrate an ultrasensitive magnetometer based on the cusp point (CP) of photon-magnon synchronization modes (PMSMs). The PMSM’s field responsivity at the CP is enhanced to $37{\gamma }_e$ and further amplified to $236{\gamma }_e$ by utilizing the sixth-order oscillating mode of the PMSM. Moreover, the emission linewidth of the PMSM can be reduced to 0.06 Hz, resulting in excellent sensitivity to weak magnetic fields. These outstanding properties position our magnetometer to potentially achieve superior sensitivity to conventional magnetometers. Our Letter introduces a cost-effective prototype for the next generation of magnetometry and may advance scientific research and technologies that rely on ultrasensitive magnetic field detection.

High-pressure environments provide a unique platform for tuning quantum phenomena, yet their applications in plasmonics remain underexplored. Here, we investigate the pressure-induced evolution of plasmons in black phosphorus films using infrared spectroscopy. Continuous pressure tuning of anisotropic plasmon resonances reveals the existence of in-plane hyperbolic plasmons, whose regime blueshifts into the mid-infrared range in the low-pressure A17 phase and collapses in the high-pressure A7 phase due to the suppressed anisotropy. Notably, we observed an exceptionally broad spectral range tuning of plasmon resonance frequency, ranging from $214{\mathrm{cm}}^{-1}$ to a maximum of $4751{\mathrm{cm}}^{-1}$, along with significant modulation in absorption intensity and anisotropy. Pronounced plasmonic anomalies at the transition point reveal phase coexistence, while the abrupt low-pressure plasmon onset signals a Lifshitz transition. Our findings establish high pressure as a novel method for tailoring plasmonic properties and unlocking new possibilities for reconfigurable nanophotonic devices.

Gaussian macroscopic fluctuation theory underpins the understanding of noise in a broad class of nonequilibrium systems. We derive exact fluctuation-response relations linking the power spectral density of stationary fluctuations to the linear response of stable nonequilibrium steady states. Both of these can be determined experimentally and used to reconstruct the kernel of the linearized dynamics and the diffusion matrix, and thus any features of the Gaussian theory. We apply our theory to gene regulatory networks with negative feedback, and derive an explicit internal-external noise decomposition of the power spectral density for any networks, including cross-correlations.

Topological multistability reflects the complexity of structure evolution inside ordered condensed matter. For a given thermodynamic system, the actual attained stable states decline sharply compared with the theoretical anticipation, which severely restricts the diversity of the material structure and properties. Here, a biphasic correlated order evolution strategy is proposed to overcome this constraint and unlock the hidden topological multistability correspondingly. Because of the remarkably varied physical properties across the phase transition point, the energetically unfavorable transformation among topological multistable states in certain phases may become favorable at adjacent phases. The concept is demonstrated in a photopatterned liquid crystal. The sample is pressed by mechanical stress of different intensities in the smectic $A$ phase to obtain several ordered textures of distinct topologies. After reheating to the nematic phase, these textures transform directly to nematic topological multistable states, which are unavailable as predicted by the string method. The modified Landau–de Gennes theory is adopted to disclose the behaviors and mechanisms of biphasic correlated order evolution, where the hidden topological multistability at nematic phase is achieved from corresponding ordered smectic $A$ states due to the topology invariance and orientational order inherence across the phase transition. The different sequences for the free energy levels of multistable states at adjacent phases corresponding to the same series of topologies are further confirmed. This Letter extends our understanding of self-organized condensed matter and may drastically enrich their diverse structures with unprecedented properties.

The stochastic dynamics of tracers arising from hydrodynamic fluctuations in a driven electrolyte is studied using a self-consistent field-theory framework in all dimensions. A plethora of scaling behavior that includes two distinct regimes of anomalous diffusion is found, and the crossovers between them are characterized in terms of the different tuning parameters. A short-time ballistic regime is found to be accessible beyond two dimensions, whereas a long-time diffusive regime is found to be present only at four dimensions and above. The results showcase how long-ranged hydrodynamic interactions can dominate the dynamics of nonequilibrium steady states in ionic suspensions and produce strong fluctuations despite the presence of Debye screening.

Standard quantum measurements are projective. However, the full scope of quantum measurements is represented by positive operator-valued measures (POVMs) and many of these break the limitations of projective measurements as resources in quantum information. It is therefore natural to consider how accurately an experimenter with access only to projective measurements and classical processing can simulate POVMs. The most well-known class of nonprojective measurements is called symmetric informationally complete (SIC). Such measurements are both ubiquitous in the broader scope of quantum information theory and known to be the most strongly nonprojective measurements in qubit systems. Here, we show that beyond qubit systems, the SIC property is in general not associated with the most nonprojective measurement. For this, we put forward a semidefinite programming criterion for detecting genuinely nonprojective measurements. This method allows us to determine quantitative simulability thresholds for generic POVMs and to put forward a conjecture on which qutrit and ququart measurements are most strongly nonprojective.

Quantum battery, as a novel energy storage device, offers the potential for unprecedented efficiency and performance beyond the capabilities of classical systems, with broad implications for future quantum technologies. Here, we experimentally demonstrate quantum charging advantage (QCA) in a scalable solid-state quantum battery. More specifically, we show how double-excitation Hamiltonians for two-level systems promote scalable QCA with standard methods. We effectively implement the collective evolution of quantum systems with two up to 12 battery cells in a superconducting quantum processor, and study the performance of quantum charging compared to its uncorrelated classical counterpart. The model considered is a linear chain of superconducting transmon qubits with only nearest-neighbor and pairwise interactions, which constitute the simplest model of a multi-cell quantum battery. Our results empirically realize substantial QCA without the necessity of adopting long-range and many-body interactions and showcase the quantum features of the QB charging processes with measurements of nonzero coherent ergotropy, incoherent ergotropy, and entanglement, revealing a promising prospect for further developments of efficient and experimentally feasible protocols for QCA.

It is of great interest to understand the thermalization of open quantum many-body systems, and how quantum computers are able to efficiently simulate that process. A recently introduced dissipative evolution, inspired by existing models of open system thermalization, has been shown to be efficiently implementable on a quantum computer. Here, we prove that, at high enough temperatures, this evolution reaches the Gibbs state in time scaling logarithmically with system size. The result holds for Hamiltonians that satisfy the Lieb-Robinson bound, such as local Hamiltonians on a lattice, and includes long-range systems. To the best of our knowledge, these are the first results rigorously establishing the rapid mixing property of high-temperature quantum Gibbs samplers, which is known to give the fastest possible speed for thermalization in the many-body setting. We then apply our result to the problem of estimating partition functions at high temperature, showing an improved performance over previous classical and quantum algorithms.

The paradigm of quantum metrology and sensing aims to identify a quantum advantage in precision at a fixed energy of the probe state. However, in practice, employing high-energy classical probes is often simpler than leveraging the quantum regime. This is not the case of covert sensing scenarios, where detection must be performed while avoiding discovery by an adversary, because increasing energy unduly facilitates the adversary. In this Letter, we introduce a general framework to assess the quantum advantage in covert situations based on extending the information bottleneck principle to decision problems via the Chernoff information. We demonstrate how entangled photonic probes paired with photon counting significantly outperform classical coherent transmitters in covert detection and ranging, often representing the only option for secrecy. Thus, our work highlights the great potential of integrating quantum sensing into lidar and radar systems to enhance covert performance.

Quantum physics enables parameter estimation with precisions beyond the capability of classical sensors. Quantum criticality is a key resource for this quantum-enhanced sensing, but experimental realization has been challenging due to the complexity of ground-state preparation and the long time required to reach the steady state near criticality. Here, we experimentally demonstrate critical enhancement in a non-Hermitian topological system using a photonic quantum walk setup. Our system supports two distinct phase transitions at which enhanced sensitivity is observed even at transient times for which the Bayesian inference shows excellent estimation and precision. It is a direct demonstration of criticality-enhanced scaling laws with nonunitary dynamics.