In active imaging protocols, information about an object is encoded into the spatial mode of a scattered photon. Recently the quantum limits of active imaging have been explored with levitated nanoparticles, which experience a multimode radiation pressure backaction (the photon recoil force) due to radiative scattering of the probe field. Here we extend the analysis of multimode backaction to compliant surfaces, accessing a broad class of mechanical resonators and fruitful analogies to quantum imaging. As an example, we consider imaging of the flexural modes of a membrane by sorting the spatial modes of a laser reflected from its surface. We show that backaction in this setting can be understood to arise from spatiotemporal photon shot noise, an effect that cannot be observed in single-mode optomechanics. We also derive the imprecision-backaction product in the limit of purely spatial (intermodal) coupling, revealing it to be equivalent to the standard quantum limit for single-mode optomechanical coupling. Finally, we show that optomechanical correlations due to spatiotemporal backaction can give rise to two-mode entangled light, providing a mechanism for entangling desired pairs of spatial modes. In conjunction with high-$Q$ nanomechanics, our findings point to new opportunities at the interface of quantum imaging and optomechanics, including sensors and networks enhanced by spatial mode entanglement.

Oscillating sessile droplets on a plane, crucial in industrial applications like inkjet printing, spray cooling, and antifogging, present a long-standing challenge in determining viscous damping. Existing solutions are limited to first-order asymptotic approximations of hemispherical droplets, accounting only for viscous dissipation near the wall. Considering further the bulk dissipation that is usually neglected due to its higher-order effect, we obtain a two-term approximation of decay rates for pinned sessile droplets with different contact angles. We demonstrate that the two-term approximation effectively resolves discrepancies between predicted and observed dampings for viscosities in the range of practical interest, supported by experiments and simulations. The two-term approximation also explains why hydrophobic droplets possess much lower damping than hydrophilic ones, and offers a template for damping prediction formulas with potential viscosity measurement applications.

We prove analytically that the two fundamental rheological equations for (elastic) disc suspensions and long flexible polymers, the so-called Oldroyd-A and -B models, respectively, predict the same flow and total stress fields in any planar incompressible flow. We illustrate this equivalence for creeping flow in a cross-slot channel and investigate differences arising from three-dimensional effects in a weakly elastic Taylor-Couette flow. Finally, we discuss implications for understanding elastic instabilities, controlling inertial turbulence, and deriving constitutive models for complex fluids.

We study the effects of polymer additives on pseudoturbulence induced by a swarm of bubbles rising in a quiescent fluid. We find that, even in the absence of background shear, beyond a critical polymer concentration, the energy spectra of velocity fluctuations in bubble-induced turbulence decay more steeply with respect to the wave number $k$. This new scaling is significantly steeper than the classical $k^{-3}$ scaling observed for bubbles in Newtonian fluids; it is independent of the gas volume fraction in the inertial limit and occurs within the length scales between the bubble wake length and the bubble diameter. Furthermore, we provide quantitative evidence that the presence of polymers enhances the coherence of the flow, as revealed by Lagrangian stretching statistics, highlighting the significant role of polymer additives in modifying the characteristics of pseudoturbulence. Our findings demonstrate that viscoelastic effects can modulate turbulence even in shear-free environments, offering a new perspective on the role of elastic stresses in complex multiphase flows.

We investigate intrinsic superconducting diode effect in the unconventional superconducting state of $d$-wave altermagnets. We find large diode efficiencies in the wide-reaching finite-momentum pairing regimes of the phase diagram. Remarkably, even perfect diode efficiency of 100% can be obtained in the presence of an external magnetic field. We attribute the largest efficiencies to competition between multiple zero-momentum (BCS) and finite-momentum superconducting states, which is connected to a topological nodal-to-nodeless transition in altermagnets with magnetic field, making our results applicable to a wide range of altermagnets.

Properties of twist grain boundaries (TGB), long known structurally but not tribologically, are simulated under sliding and load, with Au(111) our test case. The load-free TGB moiré is smooth and superlubric at incommensurate twists. Surprisingly, load provokes a first-order structural transformation, where the highest energy moiré nodes are removed—an unexpected Aubry-type transition for which we provide a Landau theory leading to a full twist-load phase diagram. Upon frictional sliding, the transformation causes a superlubric-locked transition, with a huge friction jump, and irreversible plastic flow. The predicted phenomena are robust, also recovered in a Lennard-Jones lattice TGB, and not exclusive to gold or to metals. Both superlubricity and strong Aubry locking hold promises for studies and applications in micro and nano mechanics and devices.

The rapid advancements in the semiconductor industry are often accompanied by a breakthrough in defect engineering. While defects usually hinder device performance, they can also offer new opportunities for manipulating semiconductor properties. In this Letter, we present an effective approach to solving the long-standing asymmetric injection of carriers problem in LEDs by introducing nitrogen vacancies ($V_{\mathrm{N}}$) at the GaN/AlN quantum well (QW) interface. The $V_{\mathrm{N}}$ states function as “steps” as well as sources of perturbation potential to improve the electron relaxation to the bottom of the conduction band through the electron-phonon (el-ph) coupling. The electron relaxation time (${\tau }_{\text{e}}$), initially as long as 8.61 ps, was reduced to 0.15 ps, comparable to the ${\tau }_{\mathrm{h}}$ (0.12 ps). Our work not only resolves a persistent bottleneck in GaN-based light sources but also offers a new perspective on utilizing defects to engineer carrier relaxation.

Projected entangled pair states (PEPS) are recognized as a potent tool for exploring two-dimensional quantum many-body systems. However, a significant challenge emerges when applying conventional PEPS methodologies to systems with periodic boundary conditions (PBCs), attributed to the prohibitive computational scaling with the bond dimension. This has notably restricted the study of systems with complex boundary conditions. To address this challenge, we have developed a strategy that involves the superposition of PEPS with open boundary conditions (OBCs) to treat systems with PBCs. This approach significantly reduces the computational complexity of such systems while maintaining their translational invariance and the PBCs. We benchmark this method against the Heisenberg model and the $J_1\text{−}{J}_2$ model, demonstrating its capability to yield highly accurate results at low computational costs, even for large system sizes. We further apply the method to study the Chern numbers of the hard-core Harper-Hofstadter model at different filling factors using twisted boundary conditions. This advancement significantly broadens the applicability of the PEPS approach, opening new avenues for studying a wide range of quantum many-body phenomena.

The Schmidt decomposition of quantum many-body states, which is the basis of many powerful quantum many-body techniques, relies on a partition of the whole system in terms of orthogonal local basis functions. We propose in this Letter a nonorthogonal decomposition of Slater determinants, which reduces to the conventional Schmidt decomposition in the orthogonal limit. The new decomposition provides a natural tool for building local correlation spaces when the orbitals are overlapping, which can be used to extend some existing embedding methods based on the Schmidt decomposition like density matrix embedding theory (DMET) to overlapping subsystem partitions to achieve greater flexibility and efficiency. We also propose a new quantum embedding strategy that bridges the ab initio model potential (AIMP) embedding and DMET, which circumvents the necessarity of a mean-field calculation of the whole system like AIMP, and is able to capture quantum entanglement like DMET.

We show that thermal equilibrium between conduction electrons and phonons becomes kinetically unstable when the renormalized electron-phonon coupling exceeds a certain threshold. We prove that negative electronic specific heat, $C_{\mathrm{el}}<0$, is sufficient to trigger the instability. Specifically, the instability sets in as soon as the quasiparticle weight becomes negative over a range of energies, even before $C_{\mathrm{el}}$ turns negative. This is an inherently nonequilibrium phenomenon, occurring prior to the formation of any equilibrium phase. Depending on the system, it can proceed along different pathways, ultimately resulting in a structural transition to an insulating or metallic state.

The quest to discover new 3D CFTs has been intriguing for physicists. For this purpose, fuzzy sphere regularization that studies interacting quantum systems defined on the lowest Landau level on a sphere has emerged as a powerful tool. In this Letter, we discover a series of new CFTs with global symmetry $\mathrm{Sp}(N)$ in the fuzzy sphere models that are closely related to the SO(5) deconfined phase transition, and are related to a $\mathrm{Sp}(N)/[\mathrm{Sp}(M)\times \mathrm{Sp}(N-M)]$ nonlinear sigma model with a Wess-Zumino-Witten term. We numerically verify the emergent conformal symmetry by observing the integer-spaced conformal multiplets, the quality of conformal generators, and studying the finite-size scaling of the conformality. We discuss possible candidates for these newly discovered CFTs, the most plausible ones being Chern-Simons-matter theories which have $N$ flavors of gapless bosons or fermions coupled to a non-Abelian [viz. Sp(1), Sp(2), etc.] Chern-Simons gauge field. Our Letter provides new avenues for studying interacting CFTs in 3D, possibly facilitating the nonperturbative study of critical gauge theories and previously undiscovered CFTs.

Spin-orbit coupling is a important focus of condensed matter physics as well as electron-phonon interaction. Traditionally spin-orbit coupling is regarded as a single-body effect arising from relativity, and electron-phonon interaction is often considered spin-independent. In this Letter, we bridge spin-orbit coupling and electron-phonon interaction, and propose a novel mechanism to dynamically generate spin-orbit coupling. Based on symmetry analysis, a spin-dependent electron-phonon coupling model is constructed, and is solved by sign-problem-free quantum Monte Carlo simulations. The phase diagram versus phonon frequency $\omega$ and coupling constant $\lambda$ is fully investigated. The spin-orbit coupling emerges as an order in the ground state for any $\lambda$ in the adiabatic limit, accompanied by a breathing mode of lattice distortion and a staggered loop spin current. This phase dominates in the entire range of $\omega$ with $\lambda <{\lambda }_{\infty }$, a critical value in the $\omega \to \infty$ limit. At $\lambda >{\lambda }_{\infty }$, the emergent spin-orbit coupling is suppressed as increasing $\omega$, and a phase transition occurs leading to charge-density-wave ordering degenerate with superconductivity. Our work opens up the possibility of hidden spin-orbit coupling in materials where it is otherwise forbidden by lattice symmetry and paves the way to explore possible materials for spintronics.

The quantum geometry, comprising Berry curvature and quantum metric, plays a fundamental role in governing electron transport phenomena in solids. Recent studies show that the quantum metric dipole drives scattering-free nonlinear Hall effect in topological antiferromagnets, prompting the questions of whether this effect can occur in nonmagnetic systems and be externally tuned by a magnetic field. Our work addresses these frontiers by demonstrating that the quantum metric dipole is actively tuned by an external magnetic field to generate a time-reversal-odd nonlinear Hall response in a nonmagnetic topological Dirac semimetal ${\mathrm{Cd}}_3{\mathrm{As}}_2$. Alongside the well-known chiral-anomaly-induced negative longitudinal magnetoresistance, an exotic nonlinear planar Hall effect emerges with increasing magnetic field. Careful scaling analysis indicates that this nonlinear planar Hall effect is controlled by the magnetic-field-modulated quantum metric dipole. Constructing a $k·p$ effective model of the Dirac bands under Zeeman and orbital coupling, we derive the evolution of the quantum metric dipole as a function of the magnetic field, providing a comprehensive explanation of the experimental results. Our results establish a band-structure-based strategy for engineering nonlinear magnetotransport in nonmagnetic materials via the quantum metric dipole, opening a pathway toward magnetic-field–tunable nonlinear quantum devices.

Quantum confining excitons has been a persistent challenge in the pursuit of strong exciton interactions and quantum light generation. Unlike electrons, which can be readily controlled via electric fields, imposing strong nanoscale potentials on excitons to enable quantum confinement has proven challenging. In this Letter, we utilize piezoelectric force microscopy to image the domain structures of twisted hexagonal boron nitride ($h-\mathrm{BN}$), revealing evidence of strong in-plane electric fields at the domain boundaries. By placing a monolayer ${\mathrm{MoSe}}_2$ only 1 to 2 nm away from the twisted $h-\mathrm{BN}$ interface, we observe energy splitting of neutral excitons and Fermi polarons by several millielectronvolts at the moiré domain boundaries. We attribute such observations to excitons confined in a nanoscale one-dimensional electrostatic potential created by the strong in-plane electric fields at the moiré domain boundaries. Intriguingly, this 1D quantum confinement results in pronounced polarization anisotropy in the excitons’ reflection and emission, persistent to temperatures as high as $\sim 80\mathrm{K}$. These findings open new avenues for exploring and controlling strongly interacting excitons for classical and quantum optoelectronics.

We study the ensemble of states generated by performing projective measurements on the output of a random matchgate (or free-fermionic) quantum circuit. We rigorously show that this “projected ensemble” exhibits deep thermalization: for large system sizes, it converges toward a universal ensemble that is uniform over the manifold of Gaussian fermionic states. As well as proving momentwise convergence of these ensembles, we demonstrate that the full distribution of any physical observable in the projected ensemble is close to its universal form in Wasserstein-1 distance, which we argue is an appropriate and efficiently computable measure of convergence when studying deep thermalization. Using this metric, we also numerically find that local matchgate circuits deeply thermalize after a timescale $t\sim L^2$ set by the diffusive spreading of quantum information. Our work opens up new avenues to experimentally accessible protocols to probe the emergence of quantum statistical mechanics and benchmark quantum simulators.

The interaction of a particle with vacuum fluctuations—which theoretically exist even in the complete absence of matter—can lead to observable irreversible decoherence if it were possible to switch on and off the particle charge suddenly. We compute the leading order decoherence effect for such a scenario and propose an experimental setup for its detection. Such a measurement might provide further insights into the nature of vacuum fluctuations and a novel precision test for the decoherence theory.

Pseudoentangled states are defined by their ability to hide their entanglement structure: they are indistinguishable from random states to any observer with polynomial resources, yet can have much less entanglement than random states. Existing constructions of pseudoentanglement based on phase and/or subset states are limited in the entanglement structures they can hide, e.g., the states may have low entanglement on a single cut, on all cuts at once, or on local cuts in one dimension. Here, we introduce new constructions of pseudoentangled states based on (pseudo)random tensor networks that afford much more flexibility in the achievable entanglement structures. We illustrate our construction with the simplest example of a matrix product state, realizable as a staircase circuit of pseudorandom unitary gates, which exhibits pseudo-area-law scaling of entanglement in one dimension. We then generalize our construction to arbitrary tensor network structures that admit an isometric realization. A notable application of this result is the construction of pseudoentangled “holographic” states whose entanglement entropy obeys a Ryu-Takayanagi “minimum-cut” formula, answering a question posed in Aaronson et al. [arXiv:2211.00747].