The fcc superionic phase of ice is a key component of the warm dense water phase diagram. While a few x-ray diffraction studies, under dynamic and static compressions, have reported the stability of the fcc structure, the transition to the superionic state has not been investigated in detail. Here, a remarkable thermal volume expansion is disclosed, which is interpreted as being directly related to the superionic transition. This could be achieved by implementing a heating capsule geometry within the laser-heated diamond anvil cell. Fcc ice is recovered metastable at ambient temperature, allowing us to observe that superionicity in the fcc phase emerges at a slightly lower temperature than for the bcc–fcc structural transition. The crossover in volume thermal expansion at the superionic transition agrees with recent ab initio calculations; however, its magnitude is larger than predicted.

Feshbach resonances play a vital role in the success of cold atoms investigating strongly correlated physics. The recent observation of their solid-state analog in the scattering of holes and intralayer excitons in transition metal dichalcogenides [I. Schwartz et al., Science 374, 336 (2021)] holds compelling promise for bringing fully controllable interactions to the field of semiconductors. Here, we demonstrate how tunneling-induced layer hybridization can lead to the emergence of two distinct classes of Feshbach resonances in atomically thin semiconductors. Based on microscopic scattering theory we show that these two types of Feshbach resonances allow us to tune interactions between electrons and both short-lived intralayer, as well as long-lived interlayer excitons. We predict the exciton-electron scattering phase shift from first principles and show that the exciton-electron coupling is fully tunable from strong to vanishing interactions. The tunability of interactions opens the avenue to explore Bose-Fermi mixtures in solid-state systems in regimes that were previously only accessible in cold atom experiments.

How frictional effects emerge at the microscopic level in particulate materials remains a challenging question, particularly in systems subject to thermal fluctuations due to the transient nature of interparticle contacts. Here, we directly relate particle-level frictional arrest to local coordination in an attractive colloidal model system. We reveal that the orientational dynamics of particles slows down exponentially with increasing coordination number due to the emergence of frictional interactions, the strength of which can be tuned simply by varying the attraction strength. Using a simple computer simulation model, we uncover how the interparticle interactions govern the formation of frictional contacts between particles. Our results establish quantitative relations between friction, coordination, and interparticle interactions. This is a key step toward using interparticle friction to tune the mechanical properties of particulate materials.

The realization of effective quantum error correction protocols remains a central challenge in the development of scalable quantum computers. Employing high-dimensional quantum systems (qudits) can offer more hardware-efficient protocols than qubit-based approaches. Using electron-nuclear double resonance, we implement a logical qubit encoded on the four states of a $I=3/2$ nuclear spin hyperfine-coupled to an $S=1/2$ electron spin qubit; the encoding protects against the dominant decoherence mechanism in such systems, i.e., fluctuations of the quantizing magnetic field. We explore the dynamics of the encoded state both under a controlled application of the fluctuation and under natural decoherence processes. Our results confirm the potential of these proposals for practical, implementable, fault-tolerant quantum memories.

We introduce a framework for simulating, on an ($n+1$)-qubit quantum computer, the action of a Gaussian bosonic (GB) circuit on a state over $2^n$ modes. Specifically, we encode the initial bosonic state’s expectation values over quadrature operators (and their covariance matrix) as an input qubit state. This is then evolved by a quantum circuit that effectively implements the symplectic propagators induced by the GB gates. We find families of GB circuits and initial states leading to efficient quantum simulations. For this purpose, we introduce a dictionary that maps between GB and qubit gates such that particle- (non-particle-) preserving GB gates lead to real- (imaginary-) time evolutions at the qubit level. For the special case of particle-preserving circuits, we present a bounded-error-quantum-polynomial time (BQP)-complete GB decision problem, indicating that GB evolutions of Gaussian states on exponentially many modes are as powerful as universal quantum computers. We also perform numerical simulations of an interferometer on $\sim 8\times {10}^9$ modes, illustrating the power of our framework.

We present a framework that combines the adjoint-state method together with reverse-time backpropagation to solve prohibitively large open-system quantum control problems. Our approach enables the optimization of arbitrary cost functions with fully general controls applied on large open quantum systems described by a Lindblad master equation. It is scalable, computationally efficient, and has a low-memory footprint. We apply this framework to optimize two inherently dissipative operations in superconducting qubits which lag behind in terms of fidelity and duration compared to other unitary operations: the dispersive readout and all-microwave reset of a transmon qubit. Our results show that while standard pulses for dispersive readout are nearly optimal, adding a transmon drive during the protocol can yield $2\times$ improvements in fidelity and duration. We further demonstrate a $2\times$ improvement in reset fidelity and duration through pulse shaping, indicating significant potential for enhancement in reset protocols. Our approach can readily be applied to optimize quantum controls in a vast range of applications such as reservoir engineering, autonomous quantum error correction, and leakage-reduction units.

We propose a quantum memory based on the precreated long-lived macroscopic quantum coherence. It is shown that the proposed approach provides new physical properties and methods for retrieval of the signal light fields and improvement of the basic parameters of quantum memory. We demonstrate how the precreated coherence can enable quantum storage with low quantum noise and programmable and on demand retrieval of signal light fields in atomic ensembles with natural inhomogeneous broadening. The feasibility of implementing this proposal in various crystals doped with rare earth ions, as well as in atomic gases with a Raman transition indicates, a new way for the development of optical quantum memory.

Axionlike particles (ALPs) and dark photons (DPs) are viable dark matter particle candidates. We have searched for possible ALP/DP signals in the PandaX-4T liquid xenon detector using $440\mathrm{kg}·\mathrm{yr}$ of data. A binned likelihood fit is constructed to search for possible mono-energetic peaks induced by the absorption processes between ALPs/DPs and atomic electrons of xenon. A detailed temporal model of decays associated with xenon isotopes is introduced to constrain the number of background events. No signal excess over background expectations is observed, and we have established the most stringent exclusion limits for most ALP/DP masses across the range of $150\mathrm{keV}/c^2$ to $1\mathrm{MeV}/c^2$. The improvement is particularly significant within the mass range of $150–400\mathrm{keV}/c^2$, with the average factor of 3.5 compared to previous results.

In the violent postmerger of binary neutron-star mergers strong oscillations are present that impact the emitted gravitational-wave (GW) signal. The frequencies, temperatures, and densities involved in these oscillations allow for violations of the chemical equilibrium promoted by weak interactions, thus leading to a nonzero bulk viscosity that can impact dynamics and GW signals. We present the first simulations of binary neutron-star mergers employing the self-consistent and second-order formulation of the equations of relativistic hydrodynamics for dissipative fluids proposed by Müller, Israel, and Stewart. With the spirit of obtaining a first assessment of the impact of bulk viscosity on the structure and radiative efficiency of the merger remnant we adopt a simplified but realistic approach for the viscosity, which we assume to be determined by direct and modified Urca reactions and hence to vary within the stars. At the same time, to compensate for the lack of a precise knowledge about the strength of bulk viscosity, we explore the possible behaviors by considering three different scenarios of low, medium, and high bulk viscosity. In this way, we find that large values of the bulk viscosities damp the collision-and-bounce oscillations that characterize the dynamics of the stellar cores right after the merger. At the same time, large viscosities tend to preserve the $m=2$ deformations in the remnant, thus leading to a comparatively more efficient GW emission and to changes in the postmerger spectrum that can be up to 100 Hz in the case of the most extreme configurations. Overall, our self-consistent results indicate that bulk viscosity increases the energy radiated in GWs soon after the merger by $\lesssim 2\%$ in the (realistic) scenario of small viscosity, and by $\lesssim 30\%$ in the (unrealistic) scenario of large viscosity.

We consider Carrollian conformal field theories in two dimensions and construct the boundary Carrollian conformal algebra (BCCA), opening up innumerable possibilities for further studies, given the growing relevance of Carrollian symmetries. We prove that the BCCA emerges by contracting a single copy of the Virasoro algebra. As an application, we construct, for the first time, open null strings and show that, for Dirichlet boundary conditions, we recover the BCCA as the algebra of constraints. We finally reconstruct our string results by taking the null limit of tensile open strings.

This search for magnetic monopoles (MMs) and high electric charge objects (HECOs) with spins 0, $1/2$, and 1, uses for the first time the full MoEDAL detector, exposed to $6.46{\mathrm{fb}}^{-1}$ proton-proton collisions at 13 TeV. The results are interpreted in terms of Drell-Yan and photon-fusion pair production. Mass limits on direct production of MMs of up to 10 Dirac magnetic charges and HECOs with electric charge in the range $10e$ to $400e$, were achieved. The charge limits placed on MM and HECO production are currently the strongest in the world. MoEDAL is the only LHC experiment capable of being directly calibrated for highly ionizing particles using heavy ions and with a detector system dedicated to definitively measuring magnetic charge.

We resum threshold double logarithms that appear in inclusive production of heavy quarkonium. This resolves the catastrophic failure of fixed-order perturbation theory where quarkonium cross sections at large transverse momentum can turn negative due to large radiative corrections. We find that resummation is imperative for describing measured prompt production rates of $J/\psi$ at large transverse momentum.

The subtraction function plays a pivotal role in calculations involving the forward Compton amplitude, which is crucial for predicting the Lamb shift in muonic atoms, as well as the proton-neutron mass difference. In this Letter, we present a lattice QCD calculation of the subtraction function using two domain wall fermion gauge ensembles near the physical pion mass. We utilize a recently proposed subtraction point, demonstrating its advantage in mitigating statistical and systematic uncertainties by eliminating the need for ground-state subtraction. Our results reveal significant contributions from $N\pi$ intermediate states to the subtraction function. Incorporating these contributions, we compute the proton, neutron, and nucleon isovector subtraction functions at photon momentum transfer $Q^2\in [0,2]{\mathrm{GeV}}^2$. For the proton subtraction function, we compare our lattice results with chiral perturbation theory prediction at low $Q^2$ and with the results from the perturbative operator-product expansion at high $Q^2$. Finally, using these subtraction functions as input, we determine their contribution to two-photon exchange effects in the Lamb shift and isovector nucleon electromagnetic self-energy.

The motional sideband asymmetry of a mechanical oscillator interacting with a laser field can be observed when approaching the quantum ground state, where the zero-point energy of the mechanical oscillator becomes a sizable contribution to its motion. In the context of quantum optomechanics, it allows, in principle, calibration-free inference of the thermal equilibrium of a macroscopic mechanical resonator with its optical bath. At room temperature, this phenomenon has been observed in pioneering experiments using levitated nanoparticles. Measuring this effect with solid-state mechanical resonators has been compounded by thermal intermodulation noise, mirror frequency noise and low quantum cooperativity. Here, we sideband-cool a membrane-in-the-middle system close to the quantum ground state from room temperature and observe motional sideband asymmetry in a dual-homodyne measurement. Sideband thermometry yields a minimum phonon occupancy of ${\overline{n}}_{\mathrm{eff}}=9.5$. Our work provides insights into nonlinear optomechanical dynamics at room temperature and facilitates accessible optomechanical quantum technologies without the need for complex feedback control and cryogenic cooling.

We study the dynamics of space-time nondiffracting wave packets, commonly known as light bullets, in a spatiotemporally varying medium. We show that by spatiotemporal refraction, a monochromatic focused beam can be converted to a light bullet that propagates at a given velocity. By further designing the index profile of the spatiotemporal boundary, the group velocity and the propagation direction of the light bullet can be engineered in a programmable way. All effects mentioned above cannot be achieved by spatial or temporal boundaries, and are only possible with spatiotemporal boundaries. These findings provide unique ways to engineer the dynamics of electromagnetic wave packets in space-time. Such wave packets with engineered space-time trajectory may find potential applications in the spatiotemporal control of material properties or particles, or for use as a way to emulate relativistic physics in the laboratory.

Phenomena in diverse contexts such as wetting, biological assembly, and manufacturing are attributed to the three-phase line tension. However, decades of line tension estimates based on contact angles of droplets controversially span 6 orders of magnitude, raising the question of which measurements are authoritative. Here, we show with experiments and calculations that contact angles fail to estimate line tension regardless of length scale, technique, and measurement quality. Line tension measurements based on contact angles are driven by two distinct and spurious mechanisms: body forces under ideal conditions, and data scatter under noisy conditions.

Defect engineering in two-dimensional semiconductors has been exploited to tune the optoelectronic properties and introduce new quantum states in the band gap. Chalcogen vacancies in transition metal dichalcogenides in particular have been found to strongly impact charge carrier concentration and mobility in 2D transistors as well as feature subgap emission and single-photon response. In this Letter, we investigate the layer-dependent charge-state lifetime of Se vacancies in ${\mathrm{WSe}}_2$. In one monolayer ${\mathrm{WSe}}_2$, we observe ultrafast charge transfer from the lowest unoccupied orbital of the top Se vacancy to the graphene substrate within $(1\pm 0.2)\mathrm{ps}$ measured via the current saturation in scanning tunneling approach curves. For Se vacancies decoupled by transition metal dichalcogenide (TMD) multilayers, we find a subexponential increase of the charge lifetime from $(62\pm 14)\mathrm{ps}$ in bilayer to a few nanoseconds in four-layer ${\mathrm{WSe}}_2$, alongside a reduction of the defect state binding energy. Additionally, we attribute the continuous suppression and energy shift of the $dI/dV$ in-gap defect state resonances at very close tip-sample distances to a current saturation effect. Our results provide a key measure of the layer-dependent charge transfer rate of chalcogen vacancies in TMDs.

The interplay between delocalization and repulsive interactions can cause electronic systems to undergo a Mott transition between a metal and an insulator. Here we use neural network hidden fermion determinantal states (HFDS) to uncover this transition in the disordered, fully connected Hubbard model. While dynamical mean-field theory (DMFT) provides exact solutions to physical observables of the model in the thermodynamic limit, our method allows us to directly access the wave function for finite system sizes well beyond the reach of exact diagonalization. We demonstrate how HFDS are able to obtain more accurate results in the metallic regime and in the vicinity of the transition than calculations based on a matrix product state (MPS) ansatz, for which the volume law of entanglement exhibited by the system is prohibitive. We use the HFDS method to calculate the energy and double occupancy, the quasiparticle weight and the energy gap and, importantly, the amplitudes of the wave function that provide a novel insight into this model. Our work paves the way for the study of strongly correlated electron systems with neural quantum states.

Recent experimental discovery of fractional Chern insulators at zero magnetic field in moiré superlattices has sparked intense interests in bringing Landau level physics to flat Chern bands. In twisted ${\mathrm{MoTe}}_2$ bilayers (${\mathrm{tMoTe}}_2$), recent theoretical and experimental studies have found three consecutive flat Chern bands at twist angle $\sim 2°$. In this Letter, we investigate whether higher Landau level physics can be found in these consecutive Chern bands. At twist angles 2.00° and 1.89°, we identify four consecutive $C=1$ bands for the $K$ valley in ${\mathrm{tMoTe}}_2$. By constructing Wannier functions directly from density functional theory (DFT) calculations, a six-orbital model is developed to describe the consecutive Chern bands, with the orbitals forming a honeycomb lattice. Exact diagonalization on top of Hartree-Fock calculations are carried out with the Wannier functions. Especially, when the second moiré miniband is half-filled, signatures of non-Abelian states are found. Our Wannier-based approach in modeling moiré superlattices is faithful to DFT wave functions and can serve as benchmarks for continuum models. The possibility of realizing non-Abelian anyons at zero magnetic field also opens up a new pathway for fault-tolerant quantum information processing.