In living matter, chemical gradients that populations generate and reshape often guide collective migration. Bacterial aerotaxis exemplifies this feedback between metabolism and movement, giving rise to unexpected collective behaviors. Here, we combine quantitative experiments, theoretical modeling, and numerical simulations to reveal a striking, density-dependent reversal in the migration of Escherichia coli within self-generated oxygen gradients. At low cell densities, populations retreat from the oxygen-rich interface; at high densities, they move toward it. A biophysical model in which bacteria bias their motion toward an intermediate, metabolically optimal oxygen concentration quantitatively captures this reversal and predicts a critical density at which collective migration ceases, even in the presence of sustained oxygen gradients. These findings reconcile long-standing discrepancies in observations of bacterial aerotaxis and highlight how feedback between metabolism, movement, and environmental shaping governs emergent behaviors in active matter, with potential implications for microbiome ecology.

${\mathrm{RuO}}_2$ has emerged as a prototypical candidate for altermagnetism. In the face of daunting evidence for magnetic order in the bulk, the focus naturally shifted to surfaces and ultrathin films, where Coulomb interactions are dimensionally quenched and electron correlations strongly enhanced. Here, we examine atomically ordered, ultrathin ${\mathrm{RuO}}_2\left(110\right)$ grown on $\mathrm{Ru}\left(0001\right)$ using a combination of scanning tunneling microscopy (STM), density functional theory, and density matrix renormalization group methods. We observe a nonmagnetic charge order that is imprinted by the incommensurate moiré stacking with the substrate and enhanced by the electronic Fermi-surface scattering within the flat-band surface state. We further identify a nonmagnetic, metastable $c(2\times 2)$ surface reconstruction that arises from surface phonon softening and can be toggled reversibly via STM tip manipulation. Spin-polarized STM measurements, however, reveal no evidence of magnetic order on the ${\mathrm{RuO}}_2\left(110\right)$ surface. Our findings of a nonmagnetic charge modulation position ultrathin ${\mathrm{RuO}}_2\left(110\right)$ as an intriguing platform for exploring moiré-assisted electronic orders.

Ultrarelativistic nuclear collisions create the quark-gluon plasma known as the hottest, least viscous, and most vortical fluid ever produced in terrestrial laboratories. Its vortical structure has been uncovered through the spin polarization of Lambda ($\mathrm{\Lambda }$) hyperons, attributed to the spin-orbit coupling that transfers the system’s orbital angular momentum to the quark spin, which is then inherited by hadrons via quark recombination or coalescence. However, $\mathrm{\Lambda }$ polarization reflects primarily the strange-quark component, leaving the spin dynamics of the up and down quarks largely unexplored. Although the proton is an ideal probe, its stability makes direct measurements experimentally challenging. Here, we propose to unravel proton spin polarization via hypertriton (${}_{\mathrm{\Lambda }}^3\text{H}$) measurements, exploiting the fact that spin information is preserved when polarized nucleons and $\mathrm{\Lambda }$ coalesce to form hypertriton. We show that, over a broad range of collision energies, the polarizations of proton, $\mathrm{\Lambda }$, and hypertriton are related by a simple linear scaling law. Since both $\mathrm{\Lambda }$ and hypertriton polarizations can be measured via their self-analyzing weak decays, this linear relation provides a practical experimental avenue for accessing spin polarizations of protons and neutrons—the dominant baryonic degrees of freedom in nuclear collisions.

We propose a theoretical mechanism to indirectly detect the small parity-violating energy difference (PVED) between chiral enantiomers through a macroscopic enantiomeric excess observed in an ultracold gas. We consider that chiral molecules are formed resonantly via ultracold collisions of achiral diatomic molecules, with PVED inducing a slight asymmetry in the resonance energies of right- and left-handed configurations. After formation, chiral molecules evolve within a Bose-Einstein condensate, incorporating nonlinear interactions, tunneling between enantiomeric states, intrinsic PVED, and thermal conversion rates. These collective dynamics enable amplification of the microscopic bias into a global population imbalance. Using coupled rate equations, we show that, under realistic regimes, a complete enantiomeric excess can be achieved even for extremely small intrinsic asymmetries. We illustrate the model with concrete examples (HSOH, ${\mathrm{H}}_2{\mathrm{Se}}_2, {\mathrm{H}}_2{\mathrm{Te}}_2$), predicting observable enantiomeric excesses under plausible experimental conditions. We also consider non-PVED effects that could be amplified under the proposed mechanism, including electric and magnetic fields as well as thermal fluctuations, the latter being illustrated through the aforementioned molecular examples. Overall, our results suggest that ultracold physics could provide a pathway to probe molecular parity violation, a fundamental weak effect that remains experimentally undetected.

We investigate the Yb valence instabilities in the strongly correlated YbPd compound using resonant x-ray emission spectroscopy as a function of pressure across the charge-order (CO) transition. At a low temperature ($T=30\mathrm{K}$) in the CO phase, the Yb $4f$ valence remains nearly constant up to a pressure $P_L=1.5 \pm 0.2\mathrm{GPa}$, and then increases gradually at higher pressures. In contrast, at room temperature in the normal phase, an anomalous decrease of the Yb $4f$ valence is observed, without any accompanying structural phase transition. This behavior is corroborated by a systematic pressure-dependent decrease of the unit-cell volume. Based on a Birch-Murnaghan analysis, the compressibility indicates hardening of the lattice with applied pressure up to a distinct kink seen at $P_K=1.6 \pm 0.2\mathrm{GPa}$. In contrast, for $P > P_K$, the Yb $4f$ valence saturates, and the compressibility reveals a counterintuitive pressure-induced softening. The results show a minimum in the compressibility of YbPd (with $f^0–f^1$ hole-type mixed valence), reminiscent of the maximum in compressibility seen in the $\gamma –\alpha$ first-order isostructural phase transition in cerium (with $f^0–f^1$ electron-type mixed valence).

Measurement incompatibility underpins randomness generation in nonlocal phenomena. However, at its root, a more fundamental quantum feature is noncommuting (or coherent) measurements. This raises a central question: How can we operationally characterize the quantum advantage of coherent measurements within nonlocal correlations? We answer this by demonstrating that coherent measurements can leverage semi-device-independent (SDI) steering, enabling local randomness generation from any set of coherent measurements. Specifically, we establish that a measurement assemblage can be used to demonstrate SDI steering if and only if it is coherent, providing a complete operational characterization. To provide an application of this operational characterization, we formulate a nonconvex resource theory for SDI steering and propose an operational monotone for the two-setting scenario by mapping noncommuting measurements to SDI steering. Our framework enables a practical quantum random number generator based on SDI steering that eliminates the need to certify entanglement and tolerates arbitrarily low detection efficiency. That is, we demonstrate that genuine randomness can be generated via coherent measurements beyond standard steerable states and even beyond entangled states under realistic experimental conditions. These results extend the scope of quantum resources for generating nonlocal correlations beyond measurement incompatibility, revealing the operational power of coherent measurements.

A naturally multiparameter sensing scenario arises in spatially distributed networks of quantum sensors, where each node probes a distinct parameter of interest. In such settings, the central challenges are to achieve quantum-enhanced sensitivity under well-defined resource constraints and to explicitly identify measurement strategies that attain the ultimate precision limits. Here, we analytically demonstrate quantum-enhanced sensitivity for a broad class of distributed quantum probes designed to simultaneously estimate a complete set of unknown reference-relative phase differences encoded locally. Although such locally encoded parameters can, in principle, be optimally estimated using separable strategies, our distributed protocol offers distinct advantages. In particular, for fixed network size and identical bare probe Hamiltonians, it is energetically more efficient and exhibits stroboscopic disentanglement at specific evolution times, enabling the accumulated pairwise information to be coherently mapped onto a specific subsystem. Consequently, all set of pairwise reference-relative phase differences can be accessed through a single collective measurement without requiring independent local estimation. We further construct the corresponding optimal measurement strategies and show that, within this class of probes, the ultimate multiparameter precision limits—the Holevo and quantum Cramér-Rao bounds—are saturable. We illustrate the framework with two concrete applications: simultaneous gravimetry across spatially separated locations and estimation of distributed coupling strengths. Feasibility analyses indicate that the proposed distributed quantum-enhanced sensing protocols operate within experimentally accessible regimes.

Pigmentation in mollusc shells exhibits an exceedingly diverse range of patterns that raises questions on the mechanisms underlying such diversity. This work introduces a new class of excitable systems, which extends the well-known FitzHugh-Nagumo model to allow for dynamic variation of the phase space. The phenomenon emerging from such a dynamic variation of the underlying excitable system is termed dynamic excitability. It is shown that the essential features of several classes of pigmentation patterns can be described through this unified framework of dynamic excitability, and that many of the patterns can be understood as the underlying excitable system dynamically switching between different unsteady states. A fast switch between two dynamic states is responsible for the emergence of some of the more complex pigmentation patterns observed in molluscan shells. The modeling suggests that dynamic excitability could be a universal mechanism underlying the large diversity of molluscan shell pigmentation patterns.

Artificial colloidal ice is an icelike system used to study the effects of frustration in controlled environments, where all degrees of freedom can be accessed at a length scale large enough for optical visualization and in real time. We modify this model system by inducing anisotropic interactions through an in-plane magnetic field. In this regime, the system has a well-defined ground state consisting of a checkerboard pattern of fully charged vertices. However, Brownian dynamics simulations are unable to reach this ground state and instead remain frozen in metastable disordered states, even in the absence of quenched disorder in the lattice. This arrest is caused by the local magnetic enhancement of the potential barrier that the particles need to cross to find a lower energy state.

Heavy-tailed fluctuations and power law statistics pervade physics, finance, and economics, yet their origin is often ascribed to systems poised near criticality. Here, we show that such behavior can emerge far from instability through a universal mechanism of non-normal eigenvector amplification in multidimensional Kesten processes ${\mathbf{x}}_{t+1}={\mathbf{A}}_t{\mathbf{x}}_t+{\mathit{\eta }}_t$, where ${\mathbf{A}}_t$ are random interaction $N\times N$ matrices and ${\mathit{\eta }}_t$ represents external inputs, capturing the evolving interdependence among $N$ coupled components. Even when each random multiplicative matrix is spectrally stable, nonorthogonal eigenvectors generate transient growth that renormalizes the Lyapunov exponent and decreases the tail exponent, producing stationary power laws without eigenvalues crossing the stability boundary. We derive explicit relations, first in the form of bounds and subsequently as approximations, linking the Lyapunov exponent $\gamma \sim {\gamma }_0+ln\kappa$ and the tail index $\alpha \sim -2\gamma /{\sigma }_{\kappa }^2$ to the statistics of the condition number with mean $\kappa$ and standard deviation ${\sigma }_{\kappa }$, confirmed by numerical simulations. This framework offers a unifying geometric perspective that helps interpret diverse phenomena, including polymer stretching in turbulence, magnetic-field amplification in dynamos, volatility clustering, and wealth inequality in financial systems. Non-normal interactions provide a collective route to scale-free behavior in globally stable systems, defining a universality class where multiplicative feedback and transient amplification generate critical-like statistics without spectral criticality.

Enhancing qubit connectivity in quantum processors is an important milestone for more efficient implementation of algorithms and novel error-correction protocols. While all-to-all connectivity has been demonstrated in quantum processors based on ion traps and neutral atoms, the exploration of enhanced connectivity in the superconducting qubit architecture has been a more recent endeavor. Here, we demonstrate the operation of a network comprising six superconducting transmon qubits with a novel, beyond-nearest-neighbor connectivity. We use a circular ring resonator with six qubits placed on the periphery at ${60}^{\circ }$ spacing and capacitively coupled to it in a three-dimensional circuit-QED architecture. The ring resonator acts as a two-path coupler between each pair of qubits, and we present results demonstrating that each qubit has finite coupling to three other qubits with negligible coupling to the remaining two qubits. In this architecture, with fixed-frequency qubits and always-on coupling, we benchmark the single-qubit and two-qubit gates using randomized benchmarking. We find that our gate fidelities are strongly affected by the enhanced connectivity. We characterize the spread in qubit frequencies due to cross-Kerr terms and quantify its detrimental effect on the performance of single- and two-qubit gates. Finally, we analyze the effect of the spectator qubits using numerical simulations and propose a path toward optimizing this system and achieving $>99\%$ two-qubit gate fidelities across all connected qubit pairs.

We employ, for the first time, bichromatic three-dimensional (3D) polarization-shaped ultrashort laser fields in atomic multiphoton ionization to create previously inaccessible free-electron angular momentum wave packets. The 3D fields are created by the noncollinear superposition of two polarization-shaped pulses of different colors from a supercontinuum polarization pulse shaper and provide electric-field components along all spatial directions. The resulting photoelectron momentum distributions, recorded via velocity map imaging, demonstrate full 3D quantum control of electronic superposition states extending beyond the constraints of planar polarization fields by unlocking all dipole selection rules $\mathrm{\Delta }m=0,\pm 1$. As an application, 3D pump-probe fields are used to map spin-orbit dynamics of the potassium $3d$ fine structure doublet. Our shaper-based approach establishes a route to fully controllable 3D light fields for chiral-sensitive light-matter interactions and ultrafast spectroscopy.

Due to its localized nature and controllability, the negatively charged boron vacancy centers (${\mathrm{V}}_{\text{B}}^{-}$) in hexagonal boron nitride (hBN) are a promising spin platform for accessing its neighboring nuclei with potential for performing quantum computational tasks. However, the methods of utilizing and manipulating the nuclear spins are still lacking. In this work, we propose a protocol for the preparation of single- and multiqubit gates on the nuclear spins, utilizing the electron spin as an auxiliary qubit. By applying a background magnetic field and a multitone continuous drive, we show that the electron spin coupling to the nuclei can be efficiently engineered. This allows for suppressing the undesired electron-nuclear interactions through the Hahn-echo pulse sequence. The target gates are then implemented by employing proper rf drives. Our numerical results for realistic parameters show gate fidelities as high as $99\%$ for single-qubit and $95\%$ for multiqubit gates. With the gate execution durations being less than 300 ns, our protocol evades electron spin decoherence effects. Therefore, our scheme sets the stage for the practical application of ${\mathrm{V}}_{\text{B}}^{-}$ in hBN for quantum computation purposes.

The quantum states in doubly degenerate Kramers pairs can act as an internal degree of freedom. Here, we uncover a Kramers dichroism in PT-symmetric magnets: interband transitions induced by circularly polarized light irradiation can selectively polarize Kramers partnered states allowing to control the Kramers degree of freedom. In contrast, Kramers pairs optically excited by linearly polarized light remain in a completely mixed state. Strikingly, we find a class of second-order nonlinear responses that directly track the polarization between Kramers partnered states. Such Kramers nonlinearities can be pronounced producing large second-order nonlinear layer polarization responses activated by Kramers degeneracy in layered antiferromagnets. Together with Kramers dichroism, these render optical responses a novel means for accessing the Kramers degree of freedom and diagnosing their quantum state.

We demonstrate the possibility of a genuine quantum advantage in the efficiency of quantum batteries by analyzing a model that enables a consistent comparison between quantum and classical regimes. Our system consists of $N$ harmonic oscillator cells coupled to a common thermal reservoir, evolving through Gaussian states. We define the global efficiency as the ratio of extractable work (ergotropy) to stored energy, and derive analytical bounds that distinguish, in order of increasing efficiency, regimes characterized by classical squeezing, quantum squeezing without entanglement, and genuine entanglement. Moreover, numerical simulations support the emergence of a similar hierarchy for the thermodynamic efficiency, defined as the ratio between ergotropy and the total thermodynamic cost of the charging process.

Self-organized three-dimensional (3D) ion Coulomb crystals in linear Paul traps naturally form concentric shells that provide a curved, atomically resolved interface for studying two-dimensional (2D) nanofriction. Building on prior work that used 2D ion crystals to investigate one-dimensional nanofriction and orientational melting, we leverage this foundation to extend friction studies from linear ion chains and planar rings to 3D shell structures. Using molecular-dynamics simulations, we first map shell formation as a function of ion number $N$ and the trapping aspect ratio, yielding a simple relation that can aid ion-number estimation in experiments. We compute a Peierls-Nabarro-type potential for the rotation of the outer shell against the static inner core, by treating the angle of rotation as a collective coordinate. We find that changing $N$ by just one can alter the effective rotational barrier by up to a factor of $\sim 7$, while in extreme cases changing $N$ by a few can modify the barrier by up to a factor of $\sim 60$. We quantify a geometric commensurability measure and show that the barrier reflects a system-dependent interplay between the intershell interaction, the structural response of the outer shell, and the confining potential of the trap. Using dynamical simulations, we apply rotational torques to the outer shell and identify pinned, stick-slip, and smooth-sliding regimes whose depinning thresholds depend sensitively on ion number, inner-shell geometry, and trap aspect ratio, with some configurations exhibiting hysteresis due to torque-induced metastable states. We find that spatially varying coupling to the inner-core corrugation can create coexisting fast- and slow-moving domains within the rotating outer shell, realizing multidimensional friction where intrashell shear and intershell nanofriction act simultaneously. Our results highlight the utility of self-organized ion Coulomb crystals as model systems for 2D nanofriction and open up possibilities for stabilizing complex systems and developing ultra-low-friction nanomechanical systems, such as ion-based nanorotors and torque sensors.

Variational quantum algorithms (VQAs) have emerged as promising candidates for solving complex optimization and machine learning tasks on near-term quantum hardware. However, executing quantum operations remains challenging for small-scale users because of several hardware constraints, making it desirable to delegate parts of the computation to more powerful quantum devices. In this work, we introduce a framework for delegated variational quantum algorithms, where a client with limited quantum capabilities delegates the execution of a VQA to a more powerful quantum server. In particular, we introduce a protocol that enables a client to delegate a variational quantum algorithm to a server while ensuring that the input, the output, and also the computation itself remain secret. Additionally, if the protocol does not abort, the client can be certain that the computation outcome is indeed correct. This work builds on the general verification protocol introduced by Fitzsimons and Kashefi [Phys. Rev. A 96, 012303 (2017)], tailoring it to VQAs. Our approach first proposes a verifiable protocol for delegating the quantum computation at each optimization step of a VQA and then combines the iterative steps into an error-resilient optimization process that offers end-to-end verifiable algorithm execution. We also simulate the performance of our protocol tackling the transverse field Ising model. Our results demonstrate that secure delegation of variational quantum algorithms is a realistic solution for near-term quantum networks, paving the way for practical quantum cloud computing applications.

In this paper, we propose a quantum physics-informed neural network (QPINN) to solve partial differential equations (PDEs) by using residual-based adaptive refinement (RAR). The method incorporates a residual-driven adaptive sampling mechanism into the training of QPINN, which aims to enhance convergence and accuracy by enforcing physical constraints in regions with high residuals. Then, we conduct numerical experiments on the one-dimensional viscous Burgers’ equation and diffusion equation, which have different solution structures, as well as the three-dimensional heat equation. The results show that QPINN with RAR reduces the number of parameters by about 44%, and achieves reductions of 31.65%–39.64%, 15.77%–20%, and 3.31%–23.40% over physics-informed neural network (PINN), PINN with RAR, and QPINN in mean relative $L_2$ error, respectively. In summary, it improves model convergence and solution accuracy even with limited sampling points and fewer parameters. These advantages further illustrate that QPINN with RAR is an efficient and stable pathway to solve complex and high-dimensional PDEs.

Nonequilibrium states of matter, when driven periodically, can exhibit exotic properties and emergent behaviors that are fundamentally distinct from those in equilibrium systems. To investigate the dynamical behavior of a particle system under time-periodic external forces, we performed numerical simulations of the motion of a particle initially trapped in an inverted Gaussian potential. Under strong driving, the center of motion of the particle shifts away from the origin of the trap potential, either toward the positive or negative direction. This behavior is explained by a time-averaged effective potential of the periodically driven system, which becomes double-well shaped under strong driving and thereby induces bistability with respect to the center of motion. Once the center of motion converges to either of the two local minima of the effective potential, inversion symmetry breaking occurs, giving rise to even-order harmonic generation despite the centrosymmetric nature of the original system. We show that the time-averaged position of the particle can be switched between the bistable points by additional control pulses. Conditions under which subharmonic generation occurs are also discussed. The demonstrated inversion symmetry breaking by periodic driving may lead to a scheme for manipulating localized particles and nonlinear optical responses that are inaccessible in the near-equilibrium regime.