Temperature plays a crucial role in metastable phenomena, not only by contributing to determine the state (phase) of a system, but also ruling the decay probability to more stable states. Such a situation is encountered in many different physical systems, ranging from chemical reactions to magnetic structures. The characteristic decay timescale is not always straightforward to estimate since it depends on the microscopic details of the system. A paradigmatic example in quantum field theories is the decay of the false vacuum, manifested via the nucleation of bubbles. In this Letter, we measure the temperature dependence of the timescale for the false vacuum decay mechanism in an ultracold atomic quantum spin mixture which exhibits ferromagnetic properties. Our results show that the false vacuum decay rate scales with temperature as predicted by the finite-temperature extension of the instanton theory, and confirm atomic systems as an ideal platform where to study out-of-equilibrium field theories.

We identify low-acceleration conditions under which the Unruh effect manifests as an early superradiant burst in a collection of excited atoms. The resulting amplified Unruh signal is resolved from the inertial signal both in time and intensity. We demonstrate theoretically that these conditions are realized inside a subresonant cavity that highly suppresses the response of an inertial atom, while allowing significant response from an accelerated atom as, owing to the acceleration-induced spectral broadening, it can still couple to the available field modes. The setup thus selectively amplifies the modified field fluctuations underlying the Unruh effect into an early superradiant burst. In comparison, the field fluctuations perceived inertially would cause a superradiant burst much later. In this way, we simultaneously address the extreme acceleration requirement, the weak Unruh signal, and the dominance of the inertial signal, all within a single experimental arrangement.

The mirror instability is a fundamental phenomenon in plasma physics. Given the historical discussion regarding the role of resonant particles in driving this instability—which is at odds with its presence in magnetohydrodynamic (MHD) models that only describe fluid plasma behavior—we seek to clarify the free energy source of this instability through a detailed investigation of velocity space. We introduce a method for calculating the wave-particle energy transfer rate. This diagnostic identifies that the free energy source of the mirror instability originates from nonresonant particles. This leads to a more coherent understanding of the origins of the instability within both MHD theory and plasma kinetic theory. Because of the opposing diamagnetic drift motions of the nonresonant and resonant particle populations, energy from nonresonant particles is transferred into the mirror mode waves, while resonant particles absorb energy from these waves. Consequently, both particle populations play critical roles in determining the growth rate of the linear mirror instability.

In situ x-ray diffraction at both the National Ignition Facility and Omega-EP Laser Facility has been utilized to determine the crystallographic state of ramp and shock-ramp compressed gold up to 1.2 TPa ($1\mathrm{T}\mathrm{Pa}=10\mathrm{Mbar}=10\times {10}^6$ atmospheres). In this Letter, we describe a series of experiments that explore a variety of pressure-temperature states in Au, accessed using tailored laser pulses. We find that the ambient pressure face-centered-cubic phase is stable under ramp compression to pressures of at least 1 TPa where the body-centered-cubic phase is observed simultaneously.

Understanding heat generation during charging processes of electrical double layer (EDL) systems is crucial for electrochemical technologies in practical scenarios. Existing kinetic models, attributing heat to ionic transports, however, fail to capture experimentally observed thermal behaviors in EDLs. Herein, we employ constant-potential molecular simulations to investigate heat generation in aqueous systems under nonquasistatic processes. Atomic-scale analyses via a modified kinetic equation reveal that the water-induced electric current, neglected in existing models, is essential to heat generation in both the bulk electrolyte and EDLs. In the bulk, heat deviates from Joule heating, attributed to the nonmonotonic reorientation of water dipoles driving non-Ohmic currents; within EDLs, heat exhibits damped endothermic and exothermic oscillations, originating from water reorientation that induces alternating electric fields and unidirectional currents. These findings unveil an underappreciated mechanism of heat generation governed by solvent dynamics and establish a kinetic framework for exploring thermal behavior in EDL systems.

Periodic modulation of the material index in time opens momentum gaps. Such systems are regarded as the temporal analog of common spatial crystals, wherein the band gaps open in frequency space. Recent studies have also led to the theoretical prediction of topological temporal boundary states (TTBSs) in such momentum gaps. In this Letter, we report the discovery and experimental realization of a new type of TTBS, appearing in a non-Hermitian spatial crystal with spatially periodic loss and gain, wherein the emergence of the Bloch momentum gap is associated with a parity-time broken phase, instead of relying on temporal modulation. By inducing a sudden flip of signs of the loss and gain profile, a mode emerges in the middle of the Bloch momentum gap and peaks at the flipping instant, which is regarded as a temporal boundary. Remarkably, we found that the temporal flip induces a topological transition in time, and the said mode is a TTBS that is a temporal analog of the Jackiw-Rebbi state. The TTBS is experimentally observed in a one-dimensional active mechanical lattice, and it can generically emerge in a wide range of non-Hermitian systems. By linking non-Hermitian physics with spatiotemporal topological systems, our results not only deepen the understanding of temporal topological phases but also open new grounds for controlling transient waves by topological means.

We experimentally demonstrate a method for measuring correlations of wideband magnetic signals with spatial resolution below the optical diffraction limit. Our technique employs two nitrogen-vacancy (NV) centers in diamond as nanoscale magnetometers, spectrally resolved by inhomogeneous optical transitions. Using high-fidelity optical readout and long spin coherence time, we probe correlated megahertz-range noise with sensitivity of $15\mathrm{nT}{\mathrm{Hz}}^{-1/4}$. In addition, we use this system for correlated $T_1$ relaxometry, enabling correlation measurements of gigahertz-range noise. Under such externally applied noise, while individual NV centers exhibit featureless relaxation, their correlation displays rich coherent and incoherent dynamics reminiscent of superradiance physics. This capability to probe high-frequency correlations provides a powerful tool for investigating a variety of condensed-matter phenomena characterized by nonlocal correlations.

Semi-device-independent randomness generation protocols based on Kochen-Specker contextuality offer the attractive features of compact devices, high rates, and ease of experimental implementation over fully device-independent (DI) protocols. Here, we investigate this paradigm and derive four results to improve the state of the art. Firstly, we introduce a family of simple, experimentally feasible orthogonality graphs (measurement compatibility structures) for which the maximum violation of the corresponding noncontextuality inequalities allows the certification of the maximum amount of ${\log }_{2}d$ bits of randomness from a qudit system with projective measurements for $d\ge 3$. We analytically derive the Lovász theta and fractional packing number for this graph family, and thereby prove their utility for optimal randomness generation in both randomness expansion and amplification tasks. Secondly, a central additional assumption in contextuality-based protocols over fully DI ones is that the measurements are repeatable and satisfy an intended compatibility structure. We frame a relaxation of this condition in terms of $ϵ$-orthogonality graphs for a parameter $ϵ>0$, and derive quantum correlations that allow the certification of randomness for arbitrary relaxation $ϵ\in [0,1)$. Thirdly, it is well-known that a single qubit is noncontextual, i.e., the qubit correlations can be explained by a noncontextual hidden variable model. We show however that a single qubit is almost contextual in that there exist qubit correlations that cannot be explained by $ϵ$-faithful noncontextual hidden variable models for small $ϵ>0$. Finally, we point out possible attacks by quantum and general consistent (nonsignaling) adversaries for certain classes of contextuality tests over and above those considered in DI scenarios.

We explore the dissipative phase transition of the two-photon Dicke model, a topic that has garnered significant attention recently. Our analysis reveals that while single-photon loss does not stabilize the intrinsic instability in the model, the inclusion of two-photon loss restores stability, leading to the emergence of superradiant states, which coexist with the normal vacuum states. Using a second-order cumulant expansion for the photons, we derive an analytical description of the system in the thermodynamic limit, which agrees well with the exact calculation results. Additionally, we present the Wigner function for the system, shedding light on the breaking of the $Z_4$ symmetry inherent in the model. These findings offer valuable insights into stabilization mechanisms in open quantum systems and pave the way for exploring complex nonlinear dynamics in two-photon Dicke models.

Since its first observation in the 1970s, neutrino-induced neutral-current single positive pion production ($\mathrm{NC}1{\pi }^{+}$) has remained an elusive and poorly understood interaction channel. This process is a significant background in neutrino oscillation experiments and studying it further is critical for the physics program of next-generation accelerator-based neutrino oscillation experiments. In this Letter, we present the first double-differential cross-section measurement of $\mathrm{NC}1{\pi }^{+}$ interactions using data from the ND280 detector of the T2K experiment collected in $\nu$-beam mode. The measured flux-averaged integrated cross section is $\sigma =(6.07\pm 1.22)\times {10}^{-41}{\mathrm{cm}}^2/\text{nucleon}$. We compare the results on a hydrocarbon target to the predictions of several neutrino interaction generators and final-state-interaction models. While model predictions agree with the differential results, the data show a weak preference for a cross-section normalization approximately 30% higher than predicted by most models studied in this Letter.

This Letter reports the event-by-event observation of Cherenkov light from sub-MeV electrons in a high scintillation light-yield liquid argon detector by the coherent CAPTAIN-Mills (CCM) experiment. The CCM200 detector, located at Los Alamos National Laboratory, instruments seven tons (fiducial volume) of liquid argon with 200 eight-inch photomultiplier tubes, 80% of which are coated in a wavelength-shifting material and the remaining 20% are uncoated. In the prompt time region of an event, defined as $-6\le t<0\mathrm{ns}$ relative to the event start time $t=0$, the uncoated photomultiplier tubes are primarily sensitive to visible Cherenkov photons. Using gamma rays from a ${}^{22}\mathrm{Na}$ source for production of sub-MeV electrons, we isolated prompt Cherenkov light with $>5\sigma$ confidence and developed a selection to obtain a low-background electromagnetic sample. This is the first event-by-event observation of Cherenkov photons from sub-MeV electrons in a high-yield scintillator detector and represents a milestone in low-energy particle detector development.

We propose a scheme for generating high-mass quantum superposition states of an optically precooled, levitated nanoparticle through electron diffraction at its subnanometer crystal lattice. When a single electron undergoes Bragg diffraction at a free-falling nanoparticle, momentum conservation implies that the superposition of Bragg momenta is imprinted onto the relative coordinate between electron and nanoparticle, which entangles their wave functions. By imaging the electron interferogram, one maps the nanoparticle state onto a superposition of Bragg momenta, as if it was diffracted by its own lattice. This results in a coherent momentum splitting approximately 1000 times greater than what is achievable with two-photon recoils in conventional standing-wave gratings. Self-interference of the nanoparticle can thus be observed within drastically shorter free-fall times in a time-domain Talbot interferometer configuration, significantly relaxing source requirements and alleviating decoherence from environmental factors such as residual gas and thermal radiation. Shorter interference times also allow for a recapture of the nanoparticle within its initial trapping volume, facilitating its reuse in many rapid experimental duty cycles. This opens new possibilities for experimental tests of macroscopic quantum effects within a transmission electron microscope.

The present Letter investigates a weakly pulsed granular system of polystyrene spheres under longtime microgravity conditions on the International Space Station. The spheres are measured using diffusing wave spectroscopy (DWS) and are described by mean square displacements (MSDs). Our aim is to use this technique to provide the first experimental evidence for glassy dynamics in dense granular media in microgravity and subsequently compare these results with ground-based measurements to see how the nature of these dynamics changes without the influence of gravity. Our results show that as we densify the sample in microgravity, glassy dynamics appear at a volume fraction 1.6% lower than on ground. We also show how the influence of gravity can affect how dense a granular system one can prepare by comparing the final jamming point of our sample on the ISS compared to our ground setup. We show that jamming occurs at a volume fraction 0.5% lower in space compared to on ground, showing that we can create denser states when a granular system is in the presence of a stronger gravitational field.

We establish a connection between quantum mechanics and computation, revealing fundamental limitations for algorithms computing spectra, especially in non-Hermitian settings. Introducing the concept of locally trivial pseudospectra, we show such assumptions are necessary for spectral computation. Locally trivial pseudospectra adapt dynamically to system energies, enabling spectral analysis across a broad class of challenging non-Hermitian problems. Exploiting this framework, we overcome a longstanding obstacle by computing the eigenvalues and eigenfunctions of the imaginary cubic oscillator $H_{\mathrm{B}}=p^2+i{x}^3$ with error bounds and no spurious modes—yielding, to our knowledge, the first such error-controlled result. We confirm, for instance, the 100th eigenvalue as $627.6947122484365113526737029011536\dots$. Here, truncation-induced $\mathcal{PT}$-symmetry breaking causes spurious eigenvalues—a pitfall our method avoids, highlighting the link between truncation and physics. Finally, we illustrate the approach’s generality via spectral computations for a range of physically relevant operators. This Letter provides a rigorous framework linking computational theory to quantum mechanics and offers a precise tool for spectral calculations with error bounds.