Coulomb interactions underpin the formation of excitons, yet their role in nonequilibrium exciton relaxation has remained unexplored. Here, using first-principles real-time Bethe-Salpeter formalism combined with nonadiabatic molecular dynamics, we study the ultrafast relaxation of optically bright excitons into momentum-dark states in monolayer ${\mathrm{WSe}}_2$. It is demonstrated that Coulomb-mediated couplings between excitonic configurations are strictly forbidden in a perfect lattice but are dynamically activated by phonon excitation. This activation enables the long-range Coulomb interaction to dominate exciton relaxation, reshaping kinetic pathways and surpassing conventional electron-phonon scattering. These findings reveal a new paradigm in which Coulomb interactions actively govern nonequilibrium exciton kinetics, while phonons act as a dynamical switch that unlocks many-body relaxation channels.

We explore the sensitivity of the short-baseline near detector (SBND) experiment to light dark matter using MeV-scale electromagnetic activity. Inelastic scattering of dark matter with argon nuclei can excite nuclear states that subsequently deexcite via the emission of MeV-scale photons, producing localized low-energy “blip” signatures in a liquid argon time projection chamber. We perform state-of-the-art ab initio nuclear calculations, including all relevant argon excited states with energies up to 18 MeV, to provide reliable predictions for these signals. After accounting for relevant backgrounds, we find that SBND can probe previously unexplored regions of parameter space for light dark matter.

We report atomistic simulations of subcritical crack growth rates in silica glass that quantitatively align with experimental data. This result was achieved by a careful selection of simulation cell geometry and boundary conditions, a novel crack tip tracking algorithm, a robust interatomic potential that balances accuracy with computational efficiency, and high-performance parallel computing algorithms and resources. The simulations reveal a succession of burst-arrest events that produce subcritical crack growth across a broad range of rates, extending up to kilometers per second.

The quasiparticle effective mass $m^{*}$ of the three-dimensional uniform electron gas is a fundamental Fermi-liquid parameter whose value and density dependence have remained controversial for decades. Using renormalized perturbation theory with explicit counterterms, we determine $m^{*}$ in the metallic regime ($r_s\le 6$) from first principles by two complementary routes—the self-energy and the forward-scattering four-point vertex via the $p$-wave spin-symmetric Landau parameter $F_1^s$—that agree within uncertainties at each density through the sixth renormalized order. The resulting $m^{*}/m$ remains close to unity throughout the metallic regime, with a shallow nonmonotonic density dependence—a minimum near $r_s\approx 1$ followed by a gentle upturn—reflecting the interplay of exchange and dynamical screening in the self-energy, and disfavoring strong monotonic suppression. This near-unity behavior is traced to the structural dominance of long-range charge fluctuations, whose isotropy in angular-momentum space suppresses $F_1^s$ that controls $m^{*}/m$.

Superparamagnetic collections of thermally fluctuating nanomagnet moments undergo a dynamic freezing known as a blocking transition upon cooling. The collective behavior becomes more complex when neighboring nanomagnets interact, and is further complicated when the constituent material of the nanomagnets has a temperature-dependent magnetization. Such a system can exhibit loss of ergodicity or the development of long-range order, and is experimentally accessible in artificial spin ice arrays, which provide an excellent framework for investigating ergodicity loss and equilibration on laboratory timescales. Using a macrospin model and a nonstandard Monte Carlo method, we describe the range of phase space that is thermally accessible, framing the problem within the context of the three relevant temperatures: the Curie temperature, the blocking temperature, and the collective ordering temperature of the nanomagnetic system. Our approach is generalizable and can be extended to a wide range of similar magnetic systems that are available for rigorous experimental tests.

Identifying the transition pathway for ultrafast switching between distinct antiferromagnetic orders, while holding promise to realize unprecedentedly small and fast spin devices, remains largely unexplored. Herein, we show that rectifying structure with light can serve as a powerful tool to achieve nonthermal antiferromagnetic order switching in a monolayer antiferromagnet ${\mathrm{MnPSe}}_3$. By resolving the spin-phonon coupling strength, we identify a highly selective coupling of the magnetic order with a Raman-active ${\mathrm{E}}_g$ phonon. After resonantly pumping two degenerate infrared-active ${\mathrm{E}}_u$ modes, we obtain a new metastable out-of-equilibrium state holding shifted structure along the ${\mathrm{E}}_g$ mode. Such lattice distortion offers a sustained nonthermal driving field to trigger a phase switch from a Néel-type to a zigzag-type antiferromagnetic order within the coherent phonon lifetime. By varying the pumping polarization and intensity, we provide a parameter regime for realistic light-driven magnetic phase transitions. Such an ultrafast antiferromagnetism switch can be identified by pump-probe measurements of the order-parameter-like behavior in the second harmonic generation signal or absorption spectrum.

Open quantum spin systems offer a previously unexplored route to realizing deconfined quantum criticality. We consider a spin-$1/2$ $J\text{−}{Q}_3$ chain composed of an antiferromagnetic (AFM) Heisenberg exchange and a competing multispin interaction favoring a valence-bond solid (VBS) state, with each spin component coupled to an independent bosonic bath. Combining non-Abelian bosonization and renormalization-group (RG) analysis with large-scale quantum Monte Carlo (QMC) simulations, we map out the phase diagram and characterize the associated phase transitions. We show that strong dissipation stabilizes an AFM phase for sub-Ohmic, Ohmic, and super-Ohmic baths. Continuous AFM-VBS transitions at finite dissipation are found upon increasing the multispin interaction in both the sub-Ohmic and Ohmic regimes, with their critical properties obtained through perturbative RG analysis and QMC simulations. In the Ohmic case, the critical point features spinon deconfinement and emergent O(4) symmetry. In the sub-Ohmic regime, the transition is controlled by a continuous family of nontrivial fixed points parameterized by the bath spectral exponent $s$ and may also exhibit spinon deconfinement provided that spinons remain deconfined in the dissipative VBS phase. Furthermore, in the super-Ohmic regime, we propose a transition from the AFM to the quasi-long-range ordered (QLRO) phase in addition to the QLRO-VBS transition.

Electrons photoemitted by strong laser fields can rescatter, generating attosecond high harmonics. Spectral peaks arise from inter- and intracycle interference of coherent electron wave packets. While intercycle interference is well known, intracycle interference of plateau electrons has not been observed. We present carrier-envelope phase-resolved photoemission spectra from a nanometric tungsten needle tip driven at 1570 nm revealing such interference, supported by quantum orbit and TDSE simulations that elucidate attosecond-scale electron dynamics.

The realization of scalable quantum networks for distribution of entanglement over long distances hinges on quantum repeaters. To outperform the exponential transmission loss in optical fibers, quantum repeaters must employ multiplexing schemes in the temporal, spectral, or spatial domain. The performance of such a multiplexed scheme is contingent on efficient quantum memories offering both extended storage times and large multimode capacities. Toward this goal, we experimentally demonstrate a memory platform operating at telecom wavelength using an ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_2{\mathrm{SiO}}_5$ crystal. We record on-demand storage and recall of weak coherent pulses for up to 1 ms, exceeding by an order of magnitude that of previously reported demonstrations based on ${\mathrm{Er}}^{3+}$. The memory exhibits an efficiency of 10.36% at $300\mathrm{\mu }\mathrm{s}$ storage time with a signal-to-noise ratio of 10.9, mainly limited by spontaneous emission noise. We also store two spectral modes representing a frequency-bin encoding and retrieve the state with an overlap of 81.8%. Furthermore, we demonstrate multimode capacity by simultaneously storing 20 temporal and 3 spectral modes with on-demand and selective recall capabilities, serving as a promising step toward a scalable quantum repeater architecture.

We solve Dicke superradiance with two or more competing collective decay channels of tunable rates using a symbolic quantum-trajectory construction. The method yields closed time-domain populations and observables as finite combinations of exponential terms for arbitrary numbers of emitters and arbitrary decay rates. For two channels, the behavior of the stationary ground-state distribution resembles a first-order phase transition at the point where the channel-rate ratio is equal to unity. For balanced $d$-channel decay, we obtain scaling laws for the superradiant peak time and intensity. These results unify and extend single-channel Dicke dynamics to multilevel emitters and provide a compact tool for cavity and waveguide experiments, where permutation-symmetric reservoirs engineer multiple collective decay paths.

In charge neutral fluids, such as the Dirac fluid in graphene at the Dirac point, charge transport remains diffusive despite the presence of ballistically propagating sound waves: sound waves “hydrodynamically decouple” from the slower charge fluctuations. For quasi-one-dimensional charge neutral fluids, we show that this convective charge diffusion is not smoothly connected to the normal diffusion that arises when momentum conservation is broken by noise (or static impurities). Instead, the charge diffusion constant is a discontinuous function of noise, which (in the weak-noise limit) depends only on the ratio of momentum and energy relaxation rates. In the special limit of momentum-conserving noise (e.g., spatially uniform fluctuations of the Hamiltonian), the diffusion constant diverges in the presence of noise. We describe the resulting superdiffusion in terms of coupled Burgers equations. We present a general mechanism—hydrodynamic recoupling—by which weak noise can induce singular changes in transport coefficients. Our results highlight the limits of zero-noise extrapolation for predicting dynamical quantities like diffusion constants.

The ultrastrong coupling regime of cavity photons and quantum materials has emerged as a pathway to modify materials properties. However, definitive signatures of ultrastrong coupling remain elusive. Focusing on the quantum photon statistics of light transmitted through a cavity-embedded superconductor, we show that a two-photon Higgs polariton at strong coupling realizes a photonic nonlinearity at the single terahertz photon level. We find that as light-matter coupling increases, the photon statistics show pronounced changes due to the formation of a hybrid photon-matter dark-cavity state with finite photon occupancy, producing testable signatures of ultrastrong coupling. We derive a non-Markovian input output relation and study the cavity-embedded superconductor $2{\mathrm{H}\text{−}\mathrm{NbSe}}_2$ as it approaches ultrastrong light-matter coupling. Our results reveal a diagnostic for ultrastrong coupling in the two-photon coincidence statistics that is absent in total counts.

We address the general problem of formulating the dynamical large deviations of non-Markovian systems in a closed form. Specifically, we consider a broad class of “self-interacting” jump processes whose dynamics depends on the past through a functional of a state-dependent empirical observable. Exploiting a natural separation of timescales, and under the corresponding mixing conditions, we obtain the exact (so-called “level 2.5”) large deviation joint statistics of the empirical measure over configurations and of the empirical flux of transitions. As an application of this general framework, we derive explicit general bounds on the fluctuations of trajectory observables, generalizing to the non-Markovian case both thermodynamic and kinetic uncertainty relations. We illustrate our theory with simple examples, and discuss potential applications of these results.

Speeding up the relaxation dynamics of many-body quantum systems is important in a variety of contexts, including quantum computation and state preparation. We demonstrate that such acceleration can be universally achieved via transient stochastic resetting. This means that during an initial time interval of finite duration, the dynamics is interrupted by resets that take the system to a designated state at randomly selected times. We illustrate this idea for few-body open systems and also for a challenging many-body case, where a first-order phase transition leads to a divergence of relaxation time. In all scenarios, a significant and sometimes even exponential acceleration in reaching the stationary state is observed, similar to the so-called Mpemba effect. The universal nature of this speedup lies in the fact that the design of the resetting protocol only requires knowledge of a few macroscopic properties of the target state, such as the order parameter of the phase transition, while it does not necessitate any fine-tuned manipulation of the initial state.