Hilbert space fragmentation refers to exponential growth in the number of dynamically disconnected Krylov sectors with system size. It is taken as evidence of ergodicity breaking, since conventional symmetries generate at most a polynomial number of sectors. However, we demonstrate that generalized symmetries, including higher-form, subsystem, and gauge symmetries, can have exponentially many symmetry sectors in the tensor product basis. We further prove that noninvertible symmetries can induce additional fragmentation within individual symmetry sectors. Fragmentation in several known models arises from generalized symmetries, and the presence of exponentially many Krylov sectors therefore does not by itself imply ergodicity breaking. Finally, we show that disorder free localization arises from Krylov-restricted thermalization when sectors lack translation invariance, requiring neither ergodicity breaking nor gauge symmetry.

In closed quantum dynamics, energy eigenstates represent physical excitations which, for systems with a classical limit, localize on quantized orbits in phase space. Such a picture is lacking in open systems: Liouvillians have distinct right and left eigenstates that decay with time and are difficult to interpret. We recover a physical correspondence by introducing a gauge-invariant quasiprobability measure combining right and left eigenstates that interprets a Liouvillian mode as a set of coherences, allowing one to visualize the modes as quasiprobability distributions in a “doubled” phase space. Using this measure we show that, remarkably, a damped oscillator retains its quantized “orbits” for a large class of linear and nonlinear loss, with measurable signatures. A thermal bath broadens these orbits, similar to energy levels, leading to a characteristic multistage relaxation. This provides an experimentally accessible open-system analog of the eigenstate-orbit correspondence underlying semiclassical quantization. For quadratic systems, our results yield dissipative analogs of invariant tori—a central concept in Hamiltonian systems.

The precise measurement of the leptonic CP-violating phase ${\delta }_{CP}$ remains one of the major open challenges in neutrino physics, as current experiments achieve only very limited accuracy. We address this issue through the lens of quantum estimation theory. A distinctive feature of neutrino oscillation experiments is that they cannot freely optimize the probe or measurement, since both are constrained by the production and detection of flavor eigenstates. We therefore examine whether the large uncertainty in ${\delta }_{CP}$ originates from intrinsic properties—either of the neutrino quantum state or of flavor measurements—or if it instead stems from experimental limitations. By comparing quantum and classical Fisher information, we demonstrate that the limited sensitivity to ${\delta }_{CP}$ originates primarily from the information content of flavor measurements. Furthermore, we show that, while targeting the second oscillation maximum, as in the $\mathrm{ESS}\nu \mathrm{SB}$ proposal, typically enhances ${\delta }_{CP}$ information, this feature in fact strongly depends on the actual values of ${\delta }_{CP}$.

The longitudinal structure of the quark-gluon plasma (QGP) remains poorly constrained. Using a transport-model calculation of two-particle elliptic-flow correlations $V_{2\mathrm{\Delta }}(\mathrm{\Delta }\eta )$ in relative pseudorapidity $\mathrm{\Delta }\eta$, we find two distinct initial-state components of flow decorrelation: a long-range component driven by the global geometry of participating nucleons and a short-range component reflecting local energy-deposition fluctuations. This short-range component extends to $|\mathrm{\Delta }\eta |\sim 4$ and can be misidentified as final-state nonflow. For isobarlike nuclei with different shapes, the calculation predicts an experimentally testable fingerprint of this component: it dilutes the deformation contribution at small $|\mathrm{\Delta }\eta |$, so that the $V_{2\mathrm{\Delta }}(\mathrm{\Delta }\eta )$ ratio between deformed and near-spherical systems, such as $\mathrm{U}+\mathrm{U}$-to-$\mathrm{Au}+\mathrm{Au}$, rises with $|\mathrm{\Delta }\eta |$. Separating long- and short-range flow decorrelations from nonflow gives access to the longitudinal initial structure and dynamics of the QGP.

A GAGG:Ce crystal scintillator contaminated by thorium was used to search for double-$\alpha$ decay of ${}^{224}\mathrm{Ra}$. Considering that the daughter nucleus is ${}^{216}\mathrm{Po}$ with the half-life of 0.144 s, the time-amplitude method was utilized to search for ${}^{224}\mathrm{Ra}$ $2\alpha$ events, which allows for a significant background reduction in the region of the expected effect. No double-$\alpha$ decay events were observed, allowing us to set a lower limit on the decay half-life, $\lim T_{1/2}=64\mathrm{yr}$ at 90% confidence level, which exceeds the theoretical predictions of the symmetric model of $2\alpha$ decay ($T_{1/2}=2.6\mathrm{yr}$).

Ultrahigh continuous-wave intensities $(>300\mathrm{GW}/{\mathrm{cm}}^2)$ in high-numerical-aperture optical cavities enable applications from phase-contrast electron microscopy to ultradeep dipole traps for molecules. However, the intensity can be limited by the optomechanical parametric instability (PI), where mirror vibrations scatter light from one cavity mode into another. We observe parametric instability in a tabletop Fabry-Pérot cavity, show that the mechanical modes are MHz-frequency bulk acoustic modes inside the mirrors, and measure their $Q$ factor. By using low-$Q$ mirrors, we achieve $>500\mathrm{GW}/{\mathrm{cm}}^2$ intensities in an open, free-space cavity.

We present a new “pulsating box” setup to investigate particle acceleration in high-$\beta$ plasmas undergoing compression-expansion cycles. Our fully kinetic simulations show that particles are efficiently accelerated by magnetic pumping, producing nonthermal energy distributions with power-law tails. Numerical results are in excellent agreement with a generalized maximum entropy model that we derive, linking the power-law index of distributions to the injected energy. Our results could be relevant for understanding the origin of high-energy particles in certain high-$\beta$ space and astrophysical plasmas.

Excitonic insulating (EI) and superconducting (SC) orders are generally regarded as mutually exclusive electronic instabilities. Within a self-consistent microscopic theory, we study electronic systems hosting an EI phase in the presence of SC pairing and show that an intrinsic mismatch between electron and hole Fermi surfaces fundamentally reshapes this competition. This mismatch stabilizes Fulde-Ferrell-Larkin-Ovchinnikov-like electron-hole pairing and drives spontaneous symmetry breaking of the EI state. The resulting symmetry breaking reconstructs the pairing phase space for SC and EI state, such that different regions of the Fermi surface complementarily support either EI or SC correlations, leading to a natural coexistence of the two orders. Notably, the emergent SC state consequently breaks rotational symmetry and develops intrinsic nematic superconductivity, even in the absence of explicit symmetry-breaking fields (such as magnetic fields, spin-orbit coupling, or bare band-structure anisotropy). Our results suggest that candidate materials such as monolayer $1{\mathrm{T}}^{\prime }\text{−}{\mathrm{MoTe}}_2$ and the square-net semimetal NaAlSi may provide promising platforms for observing this phenomenon. More broadly, these findings reveal a unique mechanism by which competing many-body orders generate electronic nematicity, suggesting a broader route toward spontaneous anisotropic electronic states in correlated quantum materials.

We study spin-lattice relaxation times of electron spins in ${\mathrm{Er}}^{3+}:{\mathrm{CaWO}}_4$ coupled to a low mode-volume superconducting resonator at millikelvin temperatures in a regime where resonant phonons are cooled to near their quantum ground state. At large magnetic field supporting strong phonon-emission rates, we observe a noticeable increase in relaxation times with increasing spin spectral density $c/{\mathrm{\Gamma }}_{\mathrm{inh}}$, which exhibits a $[\tanh (\hslash {\omega }_0/2k_{\mathrm{B}}T){]}^2$ contribution. These observations are typical of a phonon-bottlenecked spin relaxation, and have implications for quantum technologies that exploit rare-earth spin ensembles as coherent resources.

Ultrafast pump-probe spectroscopy is indispensable for investigating interactions, collective excitations, and nonequilibrium dynamics in superconductors and correlated electron systems. However, how a small gap opening near the Fermi surface affects the spectral changes in the high-energy interband transition region remains elusive. To address this issue, we perform systematic studies of carrier relaxation dynamics in the prototype charge-density-wave (CDW) material ${\mathrm{EuAl}}_4$. We find that the CDW gap shrinks substantially under optical pumping. This band renormalization strongly modulates interband transitions associated with the gap edge, inducing a pronounced transient reflectivity change at the corresponding probe energies. These results establish a direct link between low-energy order-parameter dynamics and high-energy spectral responses, providing a general framework for interpreting transient signals in gapped quantum materials.

Combining magnetometry with optical spectroscopy has uncovered novel quantum phenomena and is emerging as a powerful probe of quantum materials. However, the theory of the magnetic response of excitons, correlated electron-hole pairs in insulators, remains incomplete due to insufficient treatment of electron-hole interactions and quantum geometric effects. In biased bilayer graphene, for instance, theoretical predictions of valley $g$ factors for $p$ excitons deviate from experiment by nearly an order of magnitude. Here, we develop a quantum theory of the exciton orbital magnetic moment, based on first-order perturbation theory within the GW plus Bethe-Salpeter equation approach and a rigorous treatment of the position operator in the response of exciton states to a magnetic field. Our formalism reveals three distinct contributions that go beyond the heuristic approaches used in the literature: a Berry-phase-corrected single-particle electron and hole moment difference, a term from envelope-function winding linked to electron-hole relative motion, and a center-of-mass correction from exciton band quantum geometry, with the latter two being completely new effects not considered in previous studies. Our ab initio calculations yield results in excellent agreement with experiment, establishing the importance of interaction and quantum geometric effects in the magnetic response of excitons.

Walk-on-Spheres (WoS) is a particle-based technique used to describe physical phenomena as diverse as electrostatics, heat conduction, rendering, ion transport, and chemical reactions. It is fast, scalable, meshless, and applicable to geometrically complex domains, as long as the governing equations have constant coefficients. Despite these advantages, WoS has persistently struggled to deal with spatial heterogeneity, exhibiting significant loss of either accuracy or efficiency. We introduce a WoS method for parabolic and elliptic problems with spatially varying coefficients and demonstrate its superior performance through applications to heterogeneous transport phenomena. The method exhibits small bias and, where transport heterogeneity dominates the overall dynamics, a variance per sample is 1 to 2 orders of magnitude smaller than that of competing methods, including state-of-the-art WoS algorithms.

We track individual grains during the discharge of a quasi-2D silo and measure their instantaneous acceleration. This reveals collective deceleration waves which propagate upward through the packing, even though the outlet flow rate remains steady and follows the Beverloo law. Their characteristic frequency shows no systematic trend with aperture size and scales as $\sqrt{g/d}$. We model this scaling with a minimal stick-slip model along the dead zones, in which the relevant length scale is the grain diameter $d$. Introducing anisotropic magnetic interactions promote the formation of vertically aligned grain chains, which increase the characteristic length scale along the flow direction while leaving the transverse size nearly unchanged. This anisotropic elongation leads to a systematic decrease in wave frequency. Our results demonstrate that the internal flow is fundamentally intermittent and governed by grain-scale physics, in sharp contrast with the steady, aperture-controlled flow at the outlet.

Self-organized dynamic patterns in dense active matter are striking manifestations of nonequilibrium physics. A prominent example is the macroscopic elliptical motion observed in quasi-two-dimensional bacterial suspensions, whose physical origin has remained unresolved. Here, we examine a minimal linear-response framework in which the fluid mediates long-range feedback between run-and-tumble bacteria. Cross-film swimming combined with Jeffery reorientation produces a phase-leading nematic response to shear. Self-sustained oscillations arise only above a critical cell density and below a cutoff film thickness. Using independently measured single-cell and hydrodynamic parameters, the theory simultaneously accounts for the observed onset density and oscillation frequency while identifying film thickness as a primary control parameter for collective oscillations in confined active fluids. More broadly, our Letter illustrates how known microscopic dynamics and physical interactions can be combined into a predictive framework for emergent collective behavior.

The local-operator entanglement (LOE) measures the classical simulability of a Heisenberg operator and is conjectured to witness many-body chaos in locally interacting systems. Using tools from free probability, we analytically compute its asymptotic value for Haar random dynamics for all Rényi indices. We find that to the first two orders in large dimension, for traceless operators it exactly reproduces the Page curve for random states. In contrast to higher-order out-of-time-ordered correlators, which depend on more complex operator correlations via free cumulants, the leading-order LOE is independent of the initial operator. We detail exactly how these higher-order correlations are encoded in the coefficients of the finite-size corrections. Guided by our Haar result, we argue that the long-time value of the LOE entropies in chaotic systems is robust: they depend only on a simple subsector of the hierarchy of correlations encoded by the full eigenstate thermalization hypothesis. Our results therefore provide a conceptual boundary between operator simulability and higher-order scrambling diagnostics.

Nonequilibrium equations of state can provide an effective thermodynamiclike description of far-from-equilibrium systems. We experimentally construct such an equation for a direct energy cascade in a turbulent two-dimensional Bose gas. Our homogeneous gas is continuously driven on a large length scale and, with matching dissipation on a small length scale, exhibits a nonthermal but stationary power-law momentum distribution. Our equation of state links the cascade amplitude with the underlying scale-invariant energy flux, and can, for different drive strengths, gas densities, and interaction strengths, be recast into a universal power-law form using scalings consistent with the Gross-Pitaevskii model.

Measuring part of a quantum system in the midst of its evolution and acting on the result in real time is essential for numerous quantum information protocols. Neutral-atom arrays are a leading platform for quantum information processing, but their midcircuit measurement-and-feedforward cycle times have remained slow, typically exceeding 1 ms. Here, we demonstrate fast midcircuit measurement and real-time feedforward in an array of atomic qubits coupled to a high-finesse optical cavity. Local light shifts tune individual data qubits out of resonance with the cavity, shielding their coherence, while a near-resonant probe drives a selected qubit whose emission is collected with Purcell enhancement. Midcircuit measurements of four qubits with subpercent infidelity reduce the coherence of a fifth unmeasured data qubit by less than 2%. We implement real-time feedforward to correct measurement-induced phase shifts and to realize an adaptive circuit for optimal quantum-state discrimination and conditional state preparation. Our approach reduces the measurement-and-feedforward cycle time to below $100\mathrm{\mu }\mathrm{s}$ and establishes optical cavities as a route to fast control of neutral-atom quantum systems.

We theoretically propose a Hall effect driven by effective gravitational fields arising from quantum geometry. We identify four mechanisms for this “emergent-gravity Hall effect”: real-space gravity, momentum-space gravity, gravitational anomalous velocity, and gravitational Lorentz force, all of which are described by Christoffel symbols in real, momentum, or time spaces. Based on the semiclassical theory, we construct a unified theoretical framework to systematically investigate how emergent gravity in these spaces affects transport phenomena. We demonstrate these effects through model calculations and clarify the conditions under which a finite Hall response can arise. Our findings open a new avenue for exploring gravitational effects in quantum systems.