We show that a general class of node-update social impact models with higher-order interactions on hypergraphs can be exactly mapped to an equivalent model with pairwise interactions on a weighted projected network. This mapping preserves the microscopic probabilities of changing the state of the nodes. As a particular case, we introduce hypergraph-voter models, for which we compute the weights of the projected network, both analytically and numerically, across several hypergraph ensembles, and we characterize their ordering dynamics through simulations of both higher-order and reduced pairwise dynamics. For a linear social impact function (hypergraph-linear voter model), the weights of the projected network are static (state-independent), allowing us to develop a pair approximation that describes with accuracy the time evolution of macroscopic observables, which turn out to be independent of those weights. The macroscopic dynamics is thus equivalent to that of the standard voter model on the unweighted projected network. For a power-law social impact function (hypergraph-nonlinear voter model), the weights of the projected network depend on the instantaneous system configuration. Nevertheless, the nonlinear voter model on the unweighted projected network still reproduces the main macroscopic trends for well-connected hypergraphs.

Magnon-photon hybrid systems consisting of a three-dimensional electromagnetic resonator and a bulk magnetic insulator constitute the standard experimental platform in cavity magnonics. Here, we demonstrate a modular loop-gap resonator design optimized to couple with thin films of magnetic insulators. We achieve the strong-coupling regime using this loop-gap resonator coupled to a 75-nm-thick epitaxial film of yttrium iron garnet at room temperature. We further show how to perform field-differential spectroscopy of the hybrid magnon-photon system, which eliminates the unwanted signal from other loop-gap modes uncoupled to the magnetic film. In addition to the uniform ferromagnetic resonance mode, the loop-gap resonator enables a hybridization with the standing spin-wave modes forming across the thickness of the film. Our approach unlocks the use of epitaxial films and multilayers of magnetic insulators to tune the magnon band structure in cavity magnonics experiments.

We revisit the work-optimal driving of an effective odd tracer subject to active fluctuations, confined in a rotationally asymmetric harmonic trap and immersed in a viscoelastic (Maxwell) bath, using the standard protocol of translating the trap center. The odd mobility of an odd tracer need not be an intrinsic single-particle property, but can instead emerge from coarse graining over particles coupled to a viscoelastic bath. Two control schemes are considered: open loop (without measuring the active force) and closed loop (conditioned on the initial value of the active force). In the open-loop case, we show that viscoelastic memory increases the energetic cost and breaks time-reversal symmetry in the individual components of the optimal protocol, while the sum of the two protocol components can remain time symmetric. In closed-loop control, an initial measurement of the active force determines the strategy adopted by the optimal protocol. We identify the regimes of force configuration, the timescales associated with the persistence of the active force and bath relaxation, and the tracer’s odd mobility that govern optimal performance—maximizing work extraction or, equivalently, minimizing the control input. In particular, for odd tracers with specific orientations of the initial force, the interplay between the persistence time and the bath relaxation time becomes crucial, selecting an intermediate persistence that optimizes the work cost. In strongly viscoelastic regimes, we find that the cost generally increases with the bath relaxation time, reflecting the energetic penalty associated with long memory. Our results offer practical design principles for optimizing active micromachines in complex biomolecular environments, illustrating how measurement, memory, and controlled tuning of persistence can be harnessed for efficient energy conversion.

Current quantum computers require algorithms that use limited resources economically. In quantum machine learning, success hinges on quantum feature maps, which embed classical data into the state space of qubits. We introduce Quantum Feature-Map Learning via Analytic Iterative Reconstructions (Q-FLAIR), an algorithm that reduces quantum resource overhead in iterative feature-map circuit construction. It shifts workloads to a classical computer via partial analytic reconstructions of the quantum model, using only a few evaluations. For each probed gate addition to the ansatz, the simultaneous selection and optimization of the data feature and weight parameter is then entirely classical. Integrated into quantum neural network and quantum kernel support vector classifiers, Q-FLAIR shows state-of-the-art benchmark performance. Since resource overhead decouples from feature dimension, we train a quantum model on a real IBM device in only 4 h, surpassing $90\%$ accuracy on the full-resolution MNIST dataset (784 features, digits 3 versus 5). Such results were previously unattainable, as the feature dimension prohibitively drives hardware demands for fixed and search costs for adaptive ansätze. Furthermore, Q-FLAIR demonstrates dequantization robustness against direct classical modeling, satisfying a benchmark rare in the literature and a necessary condition for potential quantum advantage. By rethinking feature-map learning beyond black-box optimization, this work takes a concrete step toward enabling quantum machine learning for real-world problems and near-term quantum computers.

We numerically investigate wake dynamics in a superfluid flowing past a penetrable obstacle. The penetrable obstacle does not fully deplete the density, and we define an effective diameter $D_{\mathrm{eff}}$ from the Mach-1 contour of the time-averaged irrotational flow around the obstacle, which delineates the local supersonic region where quantized vortices nucleate. Using this flow-defined length, we construct a superfluid Reynolds number ${\mathrm{Re}}_{\mathrm{s}}\equiv (v_0-v_c)D_{\mathrm{eff}}/(\hslash /m)$, with $v_0$ being the flow speed, $v_c$ the critical velocity, and $m$ the particle mass, and show that ${\mathrm{Re}}_{\mathrm{s}}$ organizes the wake dynamics across obstacle sizes and strengths: the transition from dipole-row emission to alternating vortex cluster shedding occurs for ${\mathrm{Re}}_{\mathrm{s}}\approx 2$ and the Strouhal number and drag coefficient collapse onto universal curves versus ${\mathrm{Re}}_{\mathrm{s}}$. These results extend the notion of dynamic similarity in superfluid flows to penetrable obstacles and show that the dynamically relevant length scale is determined by the supersonic region rather than by the geometric obstacle size.

Numerical simulations of turbulent fluids are paramount to real-life applications, from predicting and modeling flows to diagnostic purposes in engineering. However, they are also computationally challenging due to their intrinsically nonlinear dynamics, which require a very high spatial resolution to accurately describe them. A promising idea is to represent flows on a discrete mesh using tensor trains (TTs), featuring a convenient scaling of the number of parameters with the mesh size. However, it is unclear how the compression power of TTs is affected by the complexity of the flows, as measured by the Reynolds number. In fact, no comprehensive analysis of how the TT representation affects the turbulent properties has yet been carried out. We fill this gap by analyzing TTs as an ansatz to compress, simulate, and generate three-dimensional (3D) snapshots with turbulentlike features. Specifically, we first investigate the effect of TT compression on key turbulence signatures, such as the energy spectrum, the probability distribution function of velocity increments, and flatness. Second, we extend the two-dimensional TT solver introduced by Peddinti et al. [Commun. Phys. 7, 135 (2024)] to a 3D cubic domain with periodic boundary conditions. We use it to simulate the incompressible Navier-Stokes dynamics at ${\text{Re}}_{\lambda }=315$ for a total of 9–10 Kolmogorov turnover times, showcasing the numerical stability of the TT solver in fully developed turbulent regimes. Third, we develop a TT algorithm to synthesize artificial snapshots that exhibit turbulentlike features, with a logarithmic cost in the mesh size. Our analysis demonstrates the ability of the TT representation to capture the characteristic features of turbulence. This offers a powerful quantum-inspired toolkit for the computational treatment of turbulent flows.

The Kondo effect is a paradigmatic model of strongly correlated physics, where a magnetic impurity forms a many-body singlet with a fermionic environment. The properties of this singlet depend sensitively on correlations within the environment, which are particularly pronounced in one dimension, where interactions give rise to Luttinger liquid behavior. A promising platform to study these effects is provided by cold gases of ytterbium (Yb) atoms, where an atomic impurity is coupled to an interacting one-dimensional fermionic environment via both magnetic and potential scattering. These two scattering mechanisms compete with each other, raising the question of how robust Kondo screening remains in such systems. Here, we show that potential scattering can suppress Kondo screening in one-dimensional Yb gases. Remarkably, however, Kondo physics persists in well-defined regimes determined by the interactions in the environment. Combining analytical renormalization-group methods with density-matrix renormalization-group simulations, we identify a transition from a strongly to a weakly entangled impurity as potential scattering increases. The two approaches are in excellent agreement across the parameter regimes considered. Our results provide a quantitative criterion for the emergence of Kondo screening in one-dimensional Yb gases and delineate experimentally accessible regimes for its realization in cold-atom platforms.

Topological bound states emerging at domain walls of dimerized chains provide a robust platform for exploring correlation effects beyond single-particle physics. When such a soliton state is coupled to a metallic substrate, local Coulomb interactions can give rise to Kondo screening. Here, we demonstrate analytically and numerically that, in an interacting Su-Schrieffer-Heeger chain, the Kondo temperature is directly controlled by the topological mass that governs the bulk gap. Near the topological transition, the Kondo scale collapses linearly with the mass parameter while retaining its exponential sensitivity to hybridization. This establishes a minimal mechanism by which a bulk topological parameter quantitatively determines an emergent many-body energy scale. Our results clarify the strong configuration dependence of soliton-induced Kondo signatures observed in graphene nanoribbon systems on Au(111) and provide experimentally testable predictions for scanning tunneling spectroscopy.

Topological gauge theories constitute a framework for understanding strongly correlated quantum matter in terms of weakly interacting composite degrees of freedom. Their topological properties become evident when these theories are realized on a space of nontrivial topology. Here, we propose a scheme to realize a one-dimensional topological gauge theory, the so-called chiral BF theory, on a ring geometry. We obtain such a theory by dimensionally reducing Chern-Simons theory on a disk to the chiral BF theory defined on the ring. Then, we encode the theory into a Hamiltonian with a coupling between angular momentum and density, and we propose and numerically benchmark its realization in an optically dressed Bose gas confined in a ring-shaped trap. There, the topological properties of the underlying theory manifest themselves through a magnetic flux variable that is density dependent. We quantify such density-dependent magnetic flux in terms of the ground-state angular momentum and the chiral properties of the system through a Bogoliubov analysis. Our proposal enables the observation of topological features of the chiral BF theory that become manifest due to the nontrivial topology of the ring geometry.

We argued in 2016 that an emf could be generated from Earth’s rotation through its own magnetic field using a magnetically permeable hollow cylinder with a low magnetic Reynolds number $R_m$ [Chyba et al., Phys. Rev. Appl. 6, 014017 (2016)]. Experiments have now generated the appropriate emf and verified five predictions of the theory [Chyba et al., Phys. Rev. Res. 7, 013285 (2025)]. Wijngaarden [Phys. Rev. Res. 8, 028001 (2026)] argues that our 2016 argument is in error. In his model, the magnetization of the cylindrical shell is due to a magnetic field that translates exactly with the velocity of the shell, giving $\mathrm{emf}=0$ always. However, we show that this only holds if magnetic diffusion is negligible, whereas in fact it is significant in the low-$R_m$ case. We do find $\mathrm{emf}=0$ in agreement with Wijngaarden for the special cases of a cylindrical shell operating at high $R_m$, or for a solid cylinder of any $R_m$. In these cases, the shell’s field does translate perfectly with the body, there is no diffusion, and current density $\mathbf{J}=\mathbf{0}$. In contrast, our device is a hollow cylinder with low $R_m$ so magnetic diffusion contributes alongside advection. For this case, the magnetic field does not rigidly translate with the shell, neither curl $\mathbf{J}$ nor $\mathbf{J}$ need vanish, and the $\mathrm{emf}$ need not be zero.

In a recent paper, Chyba et al. [Phys. Rev. Res. 7, 013285 (2025)] claim to be able to generate electrical power from Earth's rotation by a rigid device that is stationary on Earth's surface. The device is thus corotating with the surface of Earth and the generated power is claimed to originate from the motion of the device in Earth's magnetic field. Here, I show that such a device is theoretically impossible and demonstrate where precisely there are errors in the theory by Chyba et al. Also, I argue that they have not yet shown experimentally that the sub-pW power they obtained is produced by tapping the kinetic energy of Earth's rotation.

Quantum sensors are powerful devices that exploit quantum effects to detect minute quantities with extremely high precision. Two obstacles to harnessing the full capacity of quantum probes are the resource-intensive preparation of the probe and the need for sophisticated measurements that typically require full access to the entire probe. Here, we address these challenges by investigating the driven Jaynes-Cummings system undergoing a dissipative quantum phase transition as a quantum sensor. We show that detuning the system off resonance significantly improves sensing performance by adequately selecting a preferred bistable state in phase space. Our dissipative sensor, independent of the initial probe preparation, exhibits sensitivity that scales faster than linearly with respect to an effective thermodynamic resource—the strong-coupling regime ratio—for appropriate choices of parameters, and this enhanced scaling manifests in both the full system and the field subsystem. Hence, quantum-enhanced sensitivity persists even when only partial system accessibility is available. Remarkably, we show that a homodyne detection of the field state, combined with Bayesian estimation, nearly saturates the ultimate sensitivity limit of the entire system.

Lattice gauge theories (LGTs) provide a powerful framework for studying nonperturbative phenomena in gauge theories. However, conventional approaches such as Monte Carlo (MC) simulations in imaginary time are limited, as they do not allow real-time evolution and suffer from a sign problem in many important cases. Using gauged Gaussian fermionic projected entangled pair states (GGFPEPS) as a variational ground-state ansatz offers an alternative for studying LGTs through a sign-problem-free variational MC. As this method is extended to larger and more complex systems, understanding its numerical behavior becomes essential. While conventional action-based MC has been extensively studied, the performance and characteristics of non-action-based MC within the GGFPEPS framework are far less explored. In this work, we investigate these algorithmic aspects, identifying an optimal update size for GGFPEPS-based MC simulations for ${\mathbb{Z}}_2$ in $2+1$ dimensions. We show that gauge fixing generally slows convergence and demonstrate that not exploiting the translation invariance can, in some cases, improve the computational time scaling of error convergence. We expect that these improvements will allow advancing the simulation to larger and more complex systems.

The conversion between spin and orbital currents is at the origin of the orbital torque and its Onsager reciprocal, the orbital pumping. Here, we propose a phenomenological model to describe the orbital torque in magnetic bilayers composed of an orbital source (i.e., a light metal such as Ti, Ru, ${\mathrm{CuO}}_x$, etc.) and a spin-orbit coupled magnet (i.e., typically Ni, (Co/Pt)${}_n$, etc.). This approach accounts for spin-to-orbit and orbit-to-spin conversion in the ferromagnet and at the interface. We show that the orbital torque arises from a compromise between orbital current injection from the orbital source to the ferromagnet and spin current backflow from the ferromagnet back to the orbital source. We also discuss the concept of orbital-mixing conductance and introduce the “orbit-spin-mixing” and “spin-orbit-mixing” conductances that govern the orbital torque and orbital pumping, respectively.

All physical theories should obey the second law of thermodynamics. However, existing proposals to describe the dynamics of hybrid classical-quantum systems either violate the second law or lack a proof of its existence. Here, we rectify this by studying classical-quantum dynamics that are (1) linear and completely positive and (2) preserve the thermal state of the classical-quantum system. We first prove that such dynamics necessarily satisfy the second law. We then show how these dynamics may be constructed, proposing dynamics that generalize the standard Langevin and Fokker-Planck equations for classical systems in thermal environments to include backreaction from a quantum degree of freedom. Deriving necessary and sufficient conditions for completely positive, linear, and continuous classical-quantum dynamics to satisfy detailed balance, we find this property satisfied by our dynamics. To illustrate the formalism and its applications, we introduce two models. The first is an analytically solvable model of an overdamped classical system coupled to a quantum two-level system, which we use to study the total entropy production in both quantum system and classical measurement apparatus during a quantum measurement. The second describes an underdamped classical-quantum oscillator system subject to friction, which we numerically demonstrate exhibits thermalization in the adiabatic basis, showing the relevance of our dynamics for the mixed classical-quantum simulation of molecules.