Transmon qubits arise from the quantization of nonlinear resonators, systems that are prone to the buildup of strong, possibly chaotic, fluctuations. Such instabilities will likely affect fast gate operations which involve the transient population of higher excited states outside the computational subspace. Here, we extend the statistical analysis from the spectrum of the generator to that of dynamics itself and show that the instantaneous eigenphases of the time evolution operator, in particular of their curvatures, allows for identifying the subspace most affected by instabilities. Our analysis shows that fast entangling gates, operating at speeds close to the so-called quantum speed limit, contain transient regimes where the dynamics indeed becomes partially chaotic for just two transmons. Surprisingly, this does not reflect in gate reliability, rather, slower operations lead to relatively enhanced errors.

Quantum metrology has recently emerged as a powerful approach for dark matter (DM) searches, particularly using nonclassical bosonic states in microwave cavities that are sensitive to weak signals. Nonclassical cat states—macroscopic superpositions of coherent states featuring sub-Planck interference structures—offer promising advantages for high-precision measurements. However, their practical utility in DM search remains unexplored. Here, we report the first experimental application of four-component cat states within a high-quality superconducting microwave cavity to search for dark photons, a potential DM candidate. We demonstrate an 8.1-fold enhancement in the signal photon rate and constrain the dark photon kinetic mixing angle to an unprecedented $\epsilon <7.32\times {10}^{-16}$ near 6.44 GHz ($26.6\mathrm{\mu }\mathrm{eV}$). By employing a parametric sideband drive to actively tune the cavity frequency, we achieve dark photon searches and background subtraction across multiple frequency bins, yielding a sensitivity at the ${10}^{-16}$ level within a 100 kHz bandwidth. Our cat-assisted DM search and frequency-scanning techniques demonstrate substantial improvements over previous results, promising potential implications in quantum-enhanced searches for new physics.

We present updated constraints on the abundance of primordial black hole (PBH) dark matter from the high-redshift Lyman-$\alpha$ forest data from MIKE/HIRES experiments. Our analysis leverages an effective field theory (EFT) description of the 1D flux power spectrum, allowing us to analytically predict the Lyman-$\alpha$ fluctuations on quasilinear scales from first principles. Our EFT-based likelihood enables robust inference across redshifts $z=4.2–5.4$ and down to scales of 100 kpc, within previously unexplored regions of parameter space for this dataset. We derive new bounds on the PBH fraction with respect to the total dark matter $f_{\mathrm{PBH}}$, excluding populations with $f_{\mathrm{PBH}}\gtrsim {10}^{-3}$ for masses $M_{\mathrm{PBH}}\sim {10}^4–{10}^{16}{M}_{\odot }$. This offers the leading constraint for PBHs heavier than ${10}^9{M}_{\odot }$ and highlights the Lyman-$\alpha$ forest as a uniquely sensitive probe of new physics models that modify the structure formation history of our Universe.

We initiate the study of the dynamics of spherically symmetric spacetimes beyond general relativity through exact solutions of the field equations of second-order effective gravitational theories defined solely in terms of the symmetries of the problem in four or more dimensions. We prove the existence of regular Vaidya solutions that represent the formation or change in mass of regular black holes (or black hole mimickers) due to the gravitational collapse or accretion of radiation, with the time reverse of these processes being also included as solutions. Our treatment and results are remarkable in their simplicity and the breadth of possibilities they provide for novel theoretical applications and discoveries in the context of regular gravitational collapse. For instance, we illustrate how modifications of the gravitational dynamics can cure curvature singularities through what can be interpreted as an energy transfer between matter and gravitational degrees of freedom. As another application, we show how to incorporate spacetimes frequently used in the literature, designed geometrically to represent the formation and disappearance of regular black holes, as fully dynamical solutions within this formalism.

Is the usual treatment of axion dark matter as a classical field reliable? We show that the answer is subtle: the axion field could well be in a quantum state that has no complete classical description, but realistic detectors cannot tell the difference. To see this, we solve a fully quantum model of axion detection using quantum optics techniques. We show that intrinsically quantum effects are washed out by mode averaging or small amounts of noise, and significantly suppressed by the weakness of the axion coupling. Our Letter exemplifies that there should always be a classical analog for axion dark matter effects, extends to other wave (ultralight) dark-matter candidates, and gives a general method to compute the effects of exotic dark-matter states.

Using $(10087\pm 44)\times {10}^{6}J/\psi$ events collected with the BESIII detector at a center-of-mass energy of $\sqrt{s}=3.097\mathrm{GeV}$, the antihyperon-nucleon annihilation processes $\overline{\mathrm{\Lambda }}p\to K^{+}{\pi }^{+}{\pi }^{-}+k{\pi }^0$ ($k=1$, 2, 3) are studied at an incident $\overline{\mathrm{\Lambda }}$ momentum of approximately $1.074\mathrm{GeV}/c$. The reactions $\overline{\mathrm{\Lambda }}p\to K^{+}{\pi }^{+}{\pi }^{-}{\pi }^0$ and $\overline{\mathrm{\Lambda }}p\to K^{+}{\pi }^{+}{\pi }^{-}2{\pi }^0$ are observed for the first time, with corresponding cross sections ${\sigma }_{\overline{\mathrm{\Lambda }}p\to K^{+}{\pi }^{+}{\pi }^{-}{\pi }^0}={8.5}_{-1.1}^{+1.2}(\mathrm{stat})\pm 0.4(\mathrm{syst})\mathrm{mb}$ and ${\sigma }_{\overline{\mathrm{\Lambda }}p\to K^{+}{\pi }^{+}{\pi }^{-}2{\pi }^0}={7.9}_{-1.7}^{+1.9}\pm 0.4\mathrm{mb}$. No significant signal is found for $\overline{\mathrm{\Lambda }}p\to K^{+}{\pi }^{+}{\pi }^{-}3{\pi }^0$, and an upper limit of 7.2 mb is set at a 90% confidence level. Evidence for the $K^{*}(892{)}^{+}$ resonance is seen in the $K^{+}{\pi }^0$ invariant mass spectrum $M_{K^{+}{\pi }^0}$ for $k=1$, and the corresponding cross section for $\overline{\mathrm{\Lambda }}p\to K^{*}(892{)}^{+}{\pi }^{+}{\pi }^{-}$ is measured to be ${\sigma }_{\overline{\mathrm{\Lambda }}p\to K^{*}(892{)}^{+}{\pi }^{+}{\pi }^{-}}={12.5}_{-3.4}^{+3.8}\pm 1.2\mathrm{mb}$. Owing to the limited statistics, possible interference effects are not considered. These findings offer crucial input to deepen our understanding of the antihyperon-nucleon interactions.

We theoretically and experimentally investigate spontaneous self-organization in a conservative (Hamiltonian) turbulent wave system, operating far from thermodynamic equilibrium. Our system is governed by two coherently coupled nonlinear Schrödinger equations, describing the polarization evolution of light in a dispersive nonlinear optical fiber. The analysis reveals the emergence of two fundamentally distinct turbulent regimes. In a first regime, the waves undergo a slow, irreversible thermalization process, which is accurately described by the wave turbulence kinetic equation and the associated $H$ theorem of entropy growth. In stark contrast with this expected irreversible process, we identify a second different regime, where strong phase correlations spontaneously emerge, giving rise to a fast reversible oscillatory dynamics of the normal correlator and anomalous phase correlator. Experimental observations confirm the occurrence of both irreversible thermalization and reversible dynamics mediated by the anomalous correlated fluctuations.

The superconductor-insulator transition as a paradigm of quantum phase transitions has attracted tremendous interest over the past three decades. While the magnetic field and carrier density can be tuned to drive the transition, the role of disorder in the transition is not well understood due to the complicated interplay between superconductivity and electron localization. In this Letter, we controllably introduce disorder in a two-dimensional high-temperature superconductor by depositing iron clusters onto the superconducting monolayer Fe(Te,Se) crystalline film. The spectral evolution from superconducting gaps to insulating gaps with increasing disorder is detected by scanning tunneling spectroscopy measurements. When the disorder is strong, large $U$-shaped gaps are observed and attributed to the localization-enhanced Cooper pair correlation. Our observations provide insight into the emergent phases of low-dimensional and high-temperature superconductors with disorder.

We identify a symmetry that enforces every symmetric model to have a Fermi surface. These symmetry-enforced Fermi surfaces are realizations of a powerful form of symmetry-enforced gaplessness. The symmetry we construct exists in quantum lattice fermion models on a $d$-dimensional Bravais lattice, and is generated by the on-site U(1) fermion number symmetry and non-on-site Majorana translation symmetry. The resulting symmetry group is a noncompact Lie group closely related to the Onsager algebra. For a symmetry-enforced Fermi surface $\mathcal{F}$, we show that this UV symmetry group always includes the subgroup of the ersatz Fermi liquid ${\mathrm{L}}_{\mathcal{F}}\mathrm{U}(1)$ symmetry group formed by even functions $f(\mathbf{k})\in \mathrm{U}(1)$ with $\mathbf{k}\in \mathcal{F}$. Furthermore, we comment on the topology of these symmetry-enforced Fermi surfaces, proving they generically exhibit at least two noncontractible components (i.e., open orbits).

Auxiliary-field quantum Monte Carlo (AFQMC) is typically formulated as an open-ended random walk in an overcomplete space of Slater determinants, implemented through a Langevin equation. However, the explicit form of the underlying Fokker-Planck equation governing the walker population distribution has remained unknown. In this Letter, we derive the Fokker-Planck equation for AFQMC and propose a novel numerical scheme to solve it. The solution of the Fokker-Planck equation reveals the wave function actually sampled by the AFQMC algorithm. Interestingly, we find that even when the exact ground state is used as a guiding wave function in constrained path AFQMC, contrary to the common assumption, the wave function sampled by AFQMC is not exact. Beyond clarifying several fundamental aspects of AFQMC, the availability of a Fokker-Planck equation formulation opens new avenues for systematically improving its accuracy, which we outline in this Letter.

Recent progress in ultrafast x-ray sources helped establish x-rays as an important tool for probing lattice and magnetic dynamics initiated by femtosecond optical pulses. Here, we explore the potential of ultrashort hard x-ray pulses for driving magnetic dynamics. We use a transient grating technique in which a spatially periodic x-ray excitation pattern gives rise to material excitations at a well-defined wave vector, whose dynamics are monitored via diffraction of an optical probe pulse. The excitation of a ferrimagnetic gadolinium bismuth iron garnet film placed in an external tilted magnetic field by x-rays at the Gd ${\mathrm{L}}_3$ edge results in both magnetic and nonmagnetic transient gratings whose contributions to the diffracted signal are separated by polarization analysis. We observe the magnetization precession at both longitudinal acoustic and spin wave frequencies. An analysis with the Landau-Lifshitz-Gilbert equation indicates that the magnetization precession is driven by strain resulting from thermal expansion induced by absorbed x-rays. The results establish x-ray transient gratings as a tool for driving coherent phonons and magnons, with the potential of accessing wave vectors across the entire Brillouin zone.

The Anderson transition on random graphs is a paradigm for understanding high-dimensional quantum phase transitions driven by disorder and closely mirrors several features of many-body localization. In this Letter, we introduce a unitary Anderson model on small-world graphs, enabling large-scale, long-time simulations of wave-packet dynamics. This allows us to uncover logarithmically slow critical dynamics, two distinct localization times, and a crossover to ergodic diffusion. Finite-time scaling reveals distinct critical exponents, establishing a dynamical universality class for this exotic transition. Our model opens the way to an experimental realization of the Anderson transition on random graphs in quantum simulators. By combining disorder, high dimensionality, and dynamics, our approach provides a general framework for probing universal features of out-of-equilibrium quantum phase transitions, including those relevant to many-body localization.

An auto-oscillator driven by a harmonic signal at about twice its free-running frequency is characterized by a bistable phase dynamics where the two states are separated by $\pi$ radians. This phase bistability enables an oscillator to emulate a single Ising spin, providing a fundamental building block for the oscillator-based Ising machines (OIM). At the same time, a driving signal close to the oscillator free-running frequency locks the oscillator’s phase at a single value, playing the role of a magnetic field bias in ensembles of real spins. We introduce a universal theory of phase auto-oscillators driven by a biharmonic signal (having frequency components close to single and double of the free-running oscillator frequency) with noise; with it, we show how deterministic phase locking and stochastic phase slips can be continuously tuned by varying the relative amplitudes and frequencies of the driving components. Using, as an example, a spin-torque nano-oscillator, we numerically validate this theory by implementing a deterministic Ising machine paradigm, a probabilistic one, and dual-mode operation of the two. This demonstration introduces the concept of adaptive Ising machines (AIM), a unified oscillator-based architecture that dynamically combines both regimes within the same hardware platform by properly tuning the amplitudes of the biharmonic driving relative to the noise strength. Benchmarking on different classes of combinatorial optimization problems, the AIM exhibits complementary performance compared to OIMs and probabilistic Ising machines, with adaptability to the specific problem class. This Letter introduces the first OIM capable of transitioning between deterministic and probabilistic computation taking advantage of a proper design of the trade-off between the strength of phase-locking of an auto-oscillator to a biharmonic external driving and noise, opening a path toward scalable, CMOS-compatible hardware for hybrid optimization and inference.

Snap through occurs in elastic structures when a stable equilibrium configuration becomes unstable, resulting in rapid motion towards a new and distinct stable state. While static analyses of snap through are well documented, the dynamics of snap through remain underexplored, particularly in structures with natural curvature. Using a combination of finite element simulations and multiple-scales analysis, we show that the snap-through dynamics of an arch under a central point load are controlled by its slenderness and imperfections embedded in the system. As the slenderness increases, the snap-through dynamics slow down, and the mode of snap through changes from limit-point buckling to bifurcation buckling. When bifurcation buckling occurs, snap through is preceded by an extended period of oscillatory behavior. The duration of these pre-snap-through oscillations, and hence the snap-through time, is entirely controlled by imperfections in the system. Increasing the strength of imperfections dramatically reduces the snap-through time. Analytical expressions for the snap-through times are presented for limit-point and bifurcation buckling. Our Letter suggests that natural curvature and deliberately introduced imperfections can be used to tune the snap-through dynamics of new functional materials.

We perform time-domain evolutions of the ergoregion instability on a horizonless spinning ultracompact spacetime in scalar theories with potential-type and derivative self-interactions mimicking the nonlinear structure of the Einstein equations. We find that the instability saturates by triggering a weakly turbulent direct cascade, which transfers energy from the most unstable and large-scale modes to small scales. The cascade’s nonlinear timescales of each mode are orders of magnitude shorter than the corresponding linear e-folding times. Through this mechanism, the counterrotating stable light ring is filled with a spectrum of higher-order azimuthal modes forming a ringlike shape. Thereby we demonstrate that turbulent processes are likely also important during the fully gravitational saturation of the instability, leaving imprints in the gravitational wave emission.