By considering a two-level system weakly coupled to a single lossy three-dimensional cavity mode, and using a quasinormal mode expansion for the photonic medium, we show that the frequency dependence of the quantum coupling interaction between the cavity and its photonic reservoir can not be simply constructed to be independent of the cavity contents. For the single quantum dipole case, we identify the correct form of the local spectral density, revealing a surprising gauge-dependent $\sim {\omega }^{\pm 1}$ prefactor scaling, as well as a spatially dependent correction. We thus establish the correct quantum form for the cavity-reservoir interaction, which so far has only been worked out rigorously for simple 1D geometries, and show its significant impact on broadband strong coupling.

Localization phenomena during transport are typically associated with disordered scalar potentials. Here, we predict a universal pseudospin localization phenomenon driven by a disordered vectorial potential and experimentally observe its onset in an optical analog of a classical disordered spin-glass magnetic phase. In our system, disorder in the second-order nonlinear coupling of a nonlinear photonic crystal causes the idler-signal light beam, representing the pseudospin current, to approach localization in the transverse plane. This effect depends strongly on the nonlinear coupling strength, controlled by the optical pump power, revealing its inherently nonlinear nature. Furthermore, this phenomenon is marked by decaying Rabi oscillations between the idler and signal fields, linked to the disorder properties, suggesting an accompanied longitudinal decoherence effect. Our findings offer new insights into spin transport in disordered magnetic textures and open avenues for exploring complex magnetic phases and phase transitions using nonlinear optics.

Most reported negative linear compressibility (NLC) materials exhibit either a small NLC over a large pressure range or a high NLC over a very small pressure range. Here, we report the remarkable discovery of giant NLC in the low-temperature form of CuCN (LT-CuCN) over an unusually large pressure range. High-pressure XRD studies on LT-CuCN observed the NLC of $-20.5{\mathrm{TPa}}^{-1}$ along the $a$ axis at zero pressure, and the ambient orthorhombic phase remained stable up to 9.8 GPa. Pressure- and temperature-dependent Raman studies identified the phonon vibrations responsible for NLC and negative thermal expansion (NTE).

Flat bands in moiré systems are exciting new playgrounds for the generation and study of exotic many-body physics phenomena in low-dimensional materials. Such physics is attributed to the vanishing kinetic energy and strong spatial localization of the flat-band states. Here, we use numerical simulations to examine the electronic transport properties of such flat bands in magic-angle twisted bilayer graphene in the presence of disorder. We find that while a conventional downscaling of the mean free path with increasing disorder strength occurs at higher energies, in the flat bands the mean free path can actually increase with increasing disorder strength. This phenomenon is also captured by the disorder-dependent quantum metric, which is directly linked to the ground state localization. This disorder-induced delocalization suggests that weak disorder may have a strong impact on the exotic physics of magic-angle bilayer graphene and other related moiré systems.

Transition-metal-dichalcogenide heterostructures have emerged as promising platforms for realizing tunable Bose–Fermi mixtures. Their constituents are fermionic charge carriers resonantly coupled to long-lived bosonic interlayer excitons, allowing them to form trion bound states. Such platforms promise to achieve comparable densities of fermions and bosons at low relative temperatures. Here, we predict the transport properties of correlated Bose–Fermi mixtures close to a narrow solid-state Feshbach resonance. When driving a hole current, the responses of doped holes, excitons, and trions are significantly modified by the resonant interactions, leading to deviations from the typical Drude behavior and to a sign change of the exciton drag. Our results on the temperature-dependent resistivities demonstrate that near resonance interaction effects dominate over established conventional scattering mechanisms in these solid-state Bose–Fermi mixtures.

We report the detection of pure orbital currents generated by both coherent and thermal magnons in the magnetic insulator Bi-doped yttrium iron garnet (BiYIG). The pumping of orbital and spin currents is jointly investigated in nanodevices made of naturally oxidized Cu, pure Cu, Pt, and Cr. The absence of charge conduction in BiYIG and the negligible spin-to-charge conversion of oxidized Cu allows us to disambiguate the orbital current contribution. Comparative measurements on YIG and BiYIG show that the origin of the orbital pumping in BiYIG/oxidized Cu is the dynamics of the orbital magnetization in the magnetic insulator. In Cr, the pumping signal is dominated by the negative spin Hall effect rather than the positive orbital Hall effect, indicating that orbital currents represent a minority of the total angular momentum current pumped from the magnetic insulator. Our results also evidence that improving the interfacial transparency significantly enhances pumping efficiencies, not only for spin but also for orbital currents.

Moiré lattices created in two-dimensional heterostructures exhibit rich many-body physics of interacting electrons and excitons and, at the same time, suggest promising optoelectronic applications. Here, we study the cooperative radiance of moiré excitons that is demonstrated to emerge from the deep subwavelength nature of the moiré lattice and the strong excitonic on-site interaction. In particular, we show that the static dipole-dipole interaction between interlayer excitons can strongly affect their cooperative optical properties, suppressing superradiance of disordered states while enhancing superradiance of ordered phases of moiré excitons. Moreover, we show that doping permits direct control of optical cooperativity, e.g., by generating superradiant dynamics of otherwise subradiant states of excitons. Our results show that interlayer moiré excitons offer a unique platform for exploring cooperative optical phenomena in strongly interacting many-body systems, thus holding promise for applications in quantum nonlinear optics.

Rydberg states of excitons are promising quantum objects to engineer giant nonlinearities in a solid-state system. For this purpose, a deeper understanding of the dynamics of Rydberg excitons and of their potential for coherent manipulation becomes important. We report experimental results where two-photon absorption is resonant with various Rydberg states of excitons in copper oxide and we detect their emission dynamics on a streak camera with subpicosecond resolution. This technique enables the direct measurement of the Rydberg states lifetimes, which are in good agreement with the expected Rydberg scaling law. Moreover, we observe several intriguing dynamics including the presence of long-lived coherent oscillations. Finally, we independently measure the coherence time of the Rydberg states using a modified Michelson interferometer and find a good agreement with the coherent oscillations detected in the exciton emission dynamics. The lifetimes also reveal the absence of inhomogeneous broadening in the current high-precision spectroscopic data for the S series, which together with the presence of significant coherence time confirms the suitability of the system for coherent engineering.

The study of first passage time for diffusing particles reaching target states is foundational in various practical applications, including diffusion-controlled reactions. In large systems, first passage times statistics exhibit a biscaling behavior, challenging the use of a single timescale. In this work, we present a biscaling theory for the probability density function of first passage times in confined compact processes, applicable to both Euclidean and fractal domains and for diverse geometries. Our theory employs two distinct scaling functions: one for short times, capturing initial dynamics in unbounded systems, and the other for long times, which is sensitive to finite size effects. The combined framework is argued to provide a complete expression for first passage time statistics across all timescales. As our detailed calculations show, the theory describes various scenarios with and without external force fields, for active and thermal settings, and in the presence of resetting when a nonequilibrium steady state emerges.

Controlling the behavior of microswimmers is a major challenge to extract work for novel active matter applications. Geometric confinement is often used for controlling soft matter systems. However, in comparison to the case of Newtonian fluids, the effects of solid interfaces on microswimmers moving through an anisotropic fluid are far less understood. By means of nematic multiparticle collision dynamics simulations and analytical modeling, we investigate the dynamical behavior of swimmers immersed in a nematic liquid crystal and confined by solid walls. For isolated squirmers, we find a rich phase diagram including oscillatory dynamics for weak pushers, depending on the strength of their propulsion and degree of confinement. Our theoretical model shows that, unlike in the isotropic case, in a nematic fluid, force dipole, source dipole, and source quadrupole singularities all are required for the onset of oscillations. Increasing the number of squirmers shows the emergence of cooperativity in pusher-type squirmers, while pullers’ flow fields hinder each other’s motion. The interplay of nematodynamic torque, wall-induced elastic repulsion, and active flows thus offers the opportunity for both control and transport in active nematic systems.

The spatial organization of DNA involves DNA loop extrusion and the formation of protein-DNA condensates. While the significance of each process is increasingly recognized, their interplay remains unexplored. Using molecular dynamics simulation and theory we investigate this interplay. Our findings reveal that loop extrusion can enhance the dynamics of condensation and promotes coalescence and ripening of condensates. Further, the DNA loop enables condensate formation under DNA tension and position condensates. The concurrent presence of loop extrusion and condensate formation results in the formation of distinct domains similar to TADs, an outcome not achieved by either process alone.

Phages and bacteria coexist under widely different conditions, ranging from liquid cultures to oceans, soil, and the human gut. However, our models are typically limited to well-mixed liquid cultures governed by mass-action kinetics. Here, we suggest a modification to the Lotka-Volterra dynamics by including the formation of microcolonies. By analyzing the model in an open system with a steady influx of bacteria, we predict that the colony size distribution is power-low distributed with steeper exponents for the stronger external influx. In the realistic case where the phage attack rate to individual colonies is proportional to their radius, we obtain self-organization to a steady state where the maximal colony size is smaller for stronger external driving.

Quantum systems subject to random unitary evolution and measurements at random points in spacetime exhibit entanglement phase transitions which depend on the frequency of these measurements. Past work has experimentally observed entanglement phase transitions on near-term quantum computers, but the characterization approach using entanglement entropy is not scalable due to exponential overhead of quantum state tomography and postselection. Recently, an alternative protocol to detect entanglement phase transitions using linear cross entropy was proposed, attempting to eliminate both bottlenecks. Here, we report demonstrations of this protocol in systems with one-dimensional and all-to-all connectivities on IBM’s quantum hardware on up to 22 qubits, a regime which is presently inaccessible if postselection is required. We demonstrate data collapses onto scaling functions with critical exponents in semiquantitative agreement with theory. Our demonstration of the cross entropy benchmark (XEB) protocol paves the way for studies of measurement-induced entanglement phase transitions and associated critical phenomena on larger near-term quantum systems.

Quantum computers will require quantum error correction to reach the low error rates necessary for solving problems that surpass the capabilities of conventional computers. One of the dominant errors limiting the performance of quantum error correction codes across multiple technology platforms is leakage out of the computational subspace arising from the multilevel structure of qubit implementations. Here, we present a resource-efficient universal leakage reduction unit for superconducting qubits using parametric flux modulation. This operation removes leakage down to our measurement inaccuracy of $7\times {10}^{-4}$ in approximately 50 ns with a low error of $2.5(1)\times {10}^{-3}$ on the computational subspace, thereby reaching durations and fidelities comparable to those of single-qubit gates. We demonstrate that using the leakage reduction unit in repeated weight-two stabilizer measurements reduces the total number of detected errors in a scalable fashion to close to what can be achieved using leakage-rejection methods that do not scale. Our approach does not require additional control electronics or on-chip components and is applicable to both auxiliary and data qubits. These benefits make our method particularly attractive for mitigating leakage in large-scale quantum error correction circuits, a crucial requirement for the practical implementation of fault-tolerant quantum computation.

Optical cavities can provide fast and nondestructive readout of individual atomic qubits; however, scaling up to many qubits remains a challenge. Using locally addressed excited-state Stark shifts to tune atoms out of resonance, we realize site-selective hyperfine-state cavity readout across a ten-site array. The state discrimination fidelity is 0.994(1) for one atom and 0.989(2) averaged over the entire array at a survival probability of 0.975(1). To further speed up array readout, we demonstrate adaptive search strategies utilizing global or subset checks. Finally, we demonstrate repeated rounds of classical error correction, showing exponential suppression of logical error and extending logical memory fivefold beyond the single-bit idling lifetime.

We show that dark matter direct detection experiments are sensitive to the existence of particles with a small effective charge (for instance, via couplings to a kinetically mixed, low-mass dark photon). Our forecasts do not depend on these particles comprising a significant fraction of the dark matter. Rather, these experiments are sensitive to the irreducible abundance produced in the early Universe through the freeze-in mechanism. We find that ongoing and proposed direct detection experiments will have world-leading sensitivity to effective charges $Q\sim {10}^{-12}$ across 9 orders of magnitude in mass, corresponding to a dark matter subfraction as low as $\sim {10}^{-3}$.

We construct the phase space of a spherically symmetric causal diamond in ($d+2$)-dimensional Minkowski spacetime. Utilizing the covariant phase space formalism, we identify the relevant degrees of freedom that localize to the $d$-dimensional bifurcate horizon and, upon canonical quantization, determine their commutators. On this phase space, we find two Iyer-Wald charges. The first of these charges, proportional to the area of the causal diamond, is responsible for shifting the null time along the horizon and has been well documented in the literature. The second charge is much less understood, being integrable for $d\ge 2$ only if we allow for field-dependent diffeomorphisms and is responsible for changing the size of the causal diamond.