Phase transitions driven by external parameters are fundamental to condensed matter physics, providing critical insights into symmetry breaking and emergent phenomena. Recently, ferrimagnetic ${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$ has attracted considerable attention for its magnetic-field-induced insulator-metal transitions and current-driven phase transitions, but the role of applied currents in the magnetic phase remains poorly understood. Here, we employ local magnetization probes and time-resolved transport measurements to investigate the current-induced phase transitions. Magnetic force microscopy with controlled current flow reveals the evolution of ferrimagnetic domains and a first-order-like magnetic phase transition with an abrupt voltage jump. The measurements with rectangular pulsed currents reveal that the time evolution of resistance closely mirrors the resistance-temperature profile, highlighting the role of heat accumulation and a positive-feedback mechanism in the current-induced phase transitions. Furthermore, we demonstrate that the intrinsic current-voltage characteristics adhere to Ohm’s law, displaying linearity across various magnetic fields and temperatures. Our work advocates for a cautious approach in distinguishing between genuine current-induced nonequilibrium quantum states and thermal effects.

${\text{CoTi}}_2{\mathrm{O}}_5$ has the paradox that low temperature static magnetic order is incompatible with the crystal structure owing to a mirror plane that exactly frustrates magnetic interactions. Despite no observable structural distortion with diffraction, ${\text{CoTi}}_2{\mathrm{O}}_5$ does magnetically order below $T_N\sim 25\mathrm{K}$ with the breaking of spin ground state degeneracy proposed to be a realization of the spin Jahn-Teller effect in analogy to the celebrated orbital Jahn-Teller transition. We apply neutron and Raman spectroscopy to study the dynamics of this transition in ${\text{CoTi}}_2{\mathrm{O}}_5$. We find anomalous acoustics associated with a symmetry breaking strain that characterizes the spin Jahn-Teller transition. Crucially, the energy of this phonon coincides with the energy scale of the magnetic excitations, and has the same symmetry of an optic mode, observed with Raman spectroscopy, which atypically softens in energy with decreasing temperature. Taken together, we propose that the energetics of the spin Jahn-Teller effect in ${\text{CoTi}}_2{\mathrm{O}}_5$ are related to cooperative magnetoelastic fluctuations as opposed to conventional soft critical dynamics which typically drive large measurable static displacements.

Laser excitation of ${}^{229}\mathrm{Th}$ nuclei in doped wide band gap crystals has been demonstrated recently, opening the possibility of developing ultrastable solid-state clocks and sensitive searches for new physics. We develop a quantitative theory of the internal conversion (IC) of isomeric ${}^{229}\mathrm{Th}$ in solid-state hosts and elucidate a crucial requirement in choosing the solid-state hosts in nuclear clock applications. The IC of the isomer proceeds by resonantly exciting a valence band electron to a defect state, accompanied by multiphonon emission. We demonstrate that, if the process is energetically allowed, it generally quenches the isomer on a millisecond timescales, much faster than the isomer’s radiative lifetime, despite ${}^{229}\mathrm{Th}$ being in the $+4$ charge state in the valence band.

We demonstrate the use of finite-size fermionic projected entangled pair states, in conjunction with variational Monte Carlo, to perform accurate simulations of the ground state of the 2D Hubbard model. Using bond dimensions of up to $D=28$, we show that we can surpass state-of-the-art density matrix renormalization group energies that use up to $m=32000$ SU(2) multiplets on eight-leg ladders. We further apply our methodology to $10\times 16$, $12\times 16$, and $16\times 16$ lattices at $1/8$ hole doping and observe the dimensional crossover between stripe orientations. Our Letter shows the power of finite-size fermionic tensor networks to resolve the physics of the 2D Hubbard model and related problems.

The precision measurement of the tritium $\text{β}$-decay spectrum performed by the KATRIN experiment provides a unique way to search for general neutrino interactions (GNIs). All theoretically allowed GNI terms at dimension 6 involving neutrinos are incorporated into a low-energy effective field theory, and can be identified by specific signatures in the measured tritium $\text{β}$ spectrum. In this Letter an effective description of the impact of GNIs on the $\text{β}$ spectrum is formulated and the first constraints on the effective GNI parameters are derived based on the $4\times {10}^6$ electrons collected in the second measurement campaign of KATRIN in 2019. In addition, constraints on selected types of interactions are investigated, thereby exploring the potential of KATRIN to search for more specific new physics cases, including a right-handed W boson, a charged Higgs boson, or leptoquarks.

We present an extension of Landau’s theory of phase transitions by incorporating the topology of the order parameter. When the order parameter comprises several components arising from multiplicity in the same irreducible representation of symmetry, it can possess a nontrivial topology and acquire a Berry phase under the variation of thermodynamic parameters. To illustrate this idea, we investigate the superconducting phase transition of an electronic system with tetragonal symmetry and an attractive interaction involving two partial waves, both transforming in the trivial representation. By analyzing the time-dependent Ginzburg-Landau equation in the adiabatic limit, we show that the order parameter acquires a Berry phase after a cyclic evolution of parameters. We study two concrete models—one preserving time-reversal symmetry and one breaking it—and demonstrate that the nontrivial topology of the order parameter originates from thermodynamic analogs of gapless Dirac and Weyl points in the phase diagram. Finally, we identify an experimental signature of the topological Berry phase in a Josephson junction.

Quantum states featuring extensive multipartite entanglement are a resource for quantum-enhanced metrology, with sensitivity up to the Heisenberg limit. However, robust generation of these states using unitary dynamics typically requires all-to-all interactions among particles. Here, we demonstrate that optimal states for quantum sensing can be generated with sparse interaction graphs featuring only a logarithmic number of couplings per particle. We show that specific sparse graphs with long-range interactions can approximate the dynamics of all-to-all spin models, such as the one-axis twisting model, even for large system sizes. The resulting sparse coupling graphs and protocol can also be efficiently implemented using dynamic reconfiguration of atoms in optical tweezers.

The capability to measure the state of a neutral atom is vital to an atom-based quantum network, for applications including distributed quantum computing and long-distance quantum communication. However, single neutral atoms suffer from low achievable photon scattering rate and shallow trapping potential, which limits the fidelity and speed of state readout process. Here, by coupling a single neutral atom with a high-finesse fiber-based Fabry-Pérot microcavity in the Purcell regime, we realize strong enhancement of the atomic photoemission rate and high overall system efficiency, which enables ultrafast and high-fidelity discrimination of bright and dark hyperfine states of the atom. The readout fidelity can reach 99.1(2)% within 200 ns and 99.985(8)% within $9\mathrm{\mu }\mathrm{s}$. Furthermore, we demonstrate that state preparation via optical pumping can be efficiently accelerated by a real-time decision protocol based on ultrafast state readout. This work demonstrates the potential to serve as a high-performance atom-photon interface and paves the way to the implementation of a practical atom-based quantum network.

Optoelectronic metadevices control and enhance light-matter interactions by modulating the local optical field that interacts with emitters. However, the optical property of the highly localized mode in the plasmonic metasurface is sensitive to local disorders arising from experimental fluctuations. Recently, the nonlocal mode of metasurfaces has been attracting growing interest because the coupling within the array of plasmonics results in long-range ordering and collective resonances. Here we demonstrate the topological edge states and the nonlocal modes of Au bow ties in a photonic crystal (PHC) lattice. The strong coupling between plasmonic modes and PHC bands opens the topological band gap at the edge of the Brillouin zone and forms the nonlocal mode having a resonant energy insensitive to fluctuations in Au length, resulting in a robust Purcell effect for quantum dots (QDs) coupling with the nonlocal mode in metadevices. The topological band gap and robust enhancement indicate great potential for the nonlocal plasmonic metasurface in quantum photonic devices with novel functionalities.

Here we report the experimental demonstration of the nonlinear non-Hermitian skin effect (NHSE) in an effective Kerr nonlinear temporal photonic lattice, where the high-power requirements and lack of tunability intrinsic to optical materials are overcome by an artificial nonlinearity arising from optoelectronic feedforward. Thanks to Kerr self-trapping, the nonlinear NHSE is demonstrated to possess much better localization strength and robustness at the preferred boundary compared to the linear case. Away from the preferred boundary, Kerr self-trapping can even inhibit NHSE-induced transport and form stable skin solitons. Harnessing the nonlinearity-controlled NHSE, we judiciously design an optical router with a flexibly tuned output port. Our findings promise great applications in robust signal transmission, routing, and processing.

We investigate the nonlinear coupling between acoustic (ac) and optical (op) modes in the coupled magnetization dynamics of synthetic antiferromagnets, utilizing current-driven resonance spectroscopy. A clear spectral splitting is evident in the ac mode when strongly excited by the radio frequency current at a driving frequency half that of the op mode resonance. The Landau-Lifshitz phenomenology aligns with the experimental observations, affirming the coupling of the radio-frequency-excited ac and op modes through three-magnon mixing. The nonlinearity enables a Rabi-like splitting in an in-plane magnetized synthetic antiferromagnet without breaking its natural symmetries. This discovery holds potential for advancing our understanding of nonlinear antiferromagnetic dynamics.

While dual-phase xenon time projection chambers have driven the sensitivity toward weakly interacting massive particles at the $\mathrm{GeV}/c^2$ to $\mathrm{TeV}/c^2$ mass scale, the scope for sub-$\mathrm{GeV}/c^2$ dark matter particles is hindered by a limited nuclear recoil energy detection threshold. One approach to probe for lighter candidates is to consider cases where they have been boosted by collisions with cosmic rays in the Milky Way, such that the additional kinetic energy lifts their induced signatures above the nominal threshold. In this Letter, we report first results of a search for cosmic ray-boosted dark matter (CRDM) with a combined $4.2\mathrm{metric}\mathrm{ton}/\mathrm{yr}$ exposure from the LUX-ZEPLIN experiment. We observe no excess above the expected backgrounds and establish world-leading constraints on the spin-independent CRDM-nucleon cross section as small as $3.9\times {10}^{-33}{\mathrm{cm}}^2$ at 90% confidence level for sub-$\mathrm{GeV}/c^2$ masses.

Interfacial interactions often promote the emergence of unusual phenomena in two-dimensional systems, including high-temperature superconductivity. Here, we report the observation of full-gap superconductivity with a maximal spectroscopic temperature up to 26 K in a BaAs monolayer grown on ferropnictide $\mathrm{Ba}({\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x{)}_2{\mathrm{As}}_2$ (abbreviated as BFCA) epitaxial films. The superconducting gap remains robust even when the thickness of underlying BFCA is reduced to the monolayer limit, in contrast to the rapid suppression of $T_{\mathrm{c}}$ in standalone BFCA thin films. We reveal that the exceptional crystallinity of the $\mathrm{BaAs}/\mathrm{BFCA}$ heterostructures, featured by their remarkable electronic and geometric uniformities, is crucial for the emergent full-gap superconductivity with mean-field temperature dependence and pronounced bound states within magnetic vortices. Our findings open up new avenues to unravel the mysteries of unconventional superconductivity in ferropnictides and advance the development of FeAs-based heterostructures.

Smart active matter has the ability to control its motion guided by individual policies to achieve collective goals. We introduce a theoretical framework to study a decentralized learning process in which agents can locally exchange policies to adapt their behavior and maximize a predefined reward function. We use our formalism to derive explicit hydrodynamic equations for the policy dynamics. We apply the theory to two different microscopic models where policies correspond either to fixed parameters similar to evolutionary dynamics or to state-dependent controllers known from the field of robotics. We find good agreement between theoretical predictions and agent-based simulations. By deriving fundamental control parameters and uncertainty relations, our work lays the foundations for a statistical physics analysis of decentralized learning.

A highly charged muonic ion is a unique few-body atomic system where a negatively charged muon and a few electrons are simultaneously bound to a single nucleus. We report the first state-selective observation of highly charged muonic Ar ($\mu \mathrm{Ar}$) by electronic $K$ x-ray spectroscopy using an array of transition-edge sensor microcalorimeters. The high-precision $K$ x-ray spectra provide a clear signature of the presence of muonic atoms with one, two, and three electrons, i.e., H-like, He-like, and Li-like $\mu \mathrm{Ar}$. With the aid of theoretical calculations, we confirmed that the peak positions are consistent with the x-ray energies from highly charged Cl ions, and the intensities reflect deexcitation dynamics of highly charged $\mu \mathrm{Ar}$.

Acceleration of positive muons from thermal energy to 100 keV has been demonstrated. Thermal muons were generated by resonant multiphoton ionization of muonium atoms emitted from a sheet of laser-ablated aerogel. The thermal muons were first electrostatically accelerated to 5.7 keV, followed by further acceleration to 100 keV using a radio-frequency quadrupole with an intensity of $2\times {10}^{-3}{\mu }^{+}/\mathrm{pulse}$. The transverse normalized rms emittance of the accelerated muons in the horizontal and vertical planes were $0.85\pm 0.25(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}{)}_{-0.13}^{+0.22}(\mathrm{syst})\pi \mathrm{mm}\mathrm{mrad}$ and $0.32\pm 0.03{(\mathrm{stat})}_{-0.02}^{+0.05}(\mathrm{syst})\pi \mathrm{mm}\mathrm{mrad}$, respectively. The measured emittance values demonstrated phase-space reduction by a factor of $2.0\times {10}^2$ (horizontal) and $4.1\times {10}^2$ (vertical) allowing good acceleration efficiency. These results pave the way to realize the first-ever muon accelerator for a variety of applications in particle physics, material science, and other fields.

We investigate the formation and dynamics of Jones-Roberts solitons in a smoothly inhomogeneous quantum fluid. To do so, we create a superfluid of light using a paraxial, near-resonant laser beam propagating through a hot rubidium vapor. We excite a bounded vortex-antivortex dipole in the superfluid and observe its transition to a rarefaction pulse and back, in agreement with the seminal predictions of Jones and Roberts. Employing an analogy with ray optics, we calculate the trajectory of the interacting vortices, deriving an effective refractive index from the inhomogeneous fluid density. Finally, we examine analytically and experimentally the superfluid velocity correlations, observing a transfer of coherence from incompressible to compressible velocity of the quantum fluid, a direct signature of the dynamical conversion between vortices and the rarefaction pulse.

Spin-triplet pairing of superconductivity, drawing huge attention by enabling future technologies in quantum computing, spintronics, and other fields, can host unique transport phenomena. Here, we report gigantically enhanced nonreciprocal transport in the superconducting fluctuation regime of ${\mathrm{KTaO}}_3$-based interface superconductors. Notably, the observed nonreciprocity undergoes a sign reversal compared to the normal state. Combining experimental observations with theoretical modeling, we identify its dominant mechanism as the vortex motion and parity mixing of spin-singlet and spin-triplet pairings. We also provide evidence for an attractive spin-triplet pairing interaction. Furthermore, the nonreciprocal response is highly tunable by orders of magnitude using electrostatic gating. These findings shed light on the pairing mechanisms in Rashba superconductors and offer new pathways for developing nonlinear superconducting devices.

The principle of covariance, a cornerstone of modern physics, asserts the equivalence of all inertial frames of reference. Fluctuation theorems, as extensions of the second law of thermodynamics, establish universal connections between irreversibility and fluctuation in terms of stochastic thermodynamic quantities. However, these relations typically assume that both the thermodynamic system and the heat bath are at rest with respect to the observer, thereby failing to satisfy the principle of covariance. In this Letter, by introducing covariant work and heat that incorporate both energy-related and momentum-related components, we promote fluctuation theorems into covariant forms applicable to moving thermodynamic systems and moving heat baths. We illustrate this framework with two examples: the work statistics of a relativistic stochastic field and the heat statistics of a relativistic Brownian motion. Although our Letter is carried out in the context of special relativity, the results can be extended to the nonrelativistic limit. Our Letter combines the principle of covariance and fluctuation theorems into a coherent framework and may have applications in the study of thermodynamics relevant to cosmic microwave background as well as the radiative heat transfer and noncontact friction between relatively moving bodies.

Traditional studies of memory for meaningful narratives focus on specific stories and their semantic structures but do not address common quantitative features of recall across different narratives. We introduce a statistical ensemble of random trees to represent narratives as hierarchies of key points, where each node is a compressed representation of its descendant leaves, which are the original narrative segments. Recall from this hierarchical representation is constrained by working memory capacity. Our analytical solution aligns with observations from large-scale narrative recall experiments. Specifically, our model explains that (1) average recall length increases sublinearly with narrative length and (2) individuals summarize increasingly longer narrative segments in each recall sentence. Additionally, the theory predicts that for sufficiently long narratives, a universal, scale-invariant limit emerges, where the fraction of a narrative summarized by a single recall sentence follows a distribution independent of narrative length.