During laser-induced phase transitions, fast transformations of electronic, atomic, and spin configurations often involve the emergence of hidden and metastable phases. Being inaccessible under any other stimuli, such phases are indispensable for unveiling mechanisms and controlling the transitions. We experimentally explore spin kinetics during the ultrafast first-order 90° spin-reorientation (SR) transition in a canted antiferromagnet ${\mathrm{Fe}}_3{\mathrm{BO}}_6$, and reveal that the transition is controlled by canting between the magnetic sublattices. Laser-induced perturbation of the Dzyaloshinskii-Moriya interaction results in a change of the intersublattice canting within the first picoseconds, bringing ${\mathrm{Fe}}_3{\mathrm{BO}}_6$ to a hidden phase. Once this phase emerges, laser-induced heating activates precessional 90° spin switching. The combination of spin canting and heating controls the final spin configuration comprising coexisting initial and switched phases. The extended phase coexistence range is in striking contrast to the narrow SR transition in ${\mathrm{Fe}}_3{\mathrm{BO}}_6$ induced by conventional heating.

Altermagnets, a newly discovered class of magnets, integrate the advantages of both ferromagnets and antiferromagnets, such as enabling anomalous transport without stray fields and supporting ultrafast spin dynamics, offering exciting opportunities for spintronics. A key challenge in altermagnetic spintronics is the efficient reading and writing of information by switching the Néel vector orientations to represent binary “0” and “1.” Here, we develop a microscopic theory of the magnetoresistance effect in altermagnets and propose that magnetoresistance anisotropy can serve as an effective mechanism for the electrical readout of the Néel vector. Our theory describes a two-step charge-spin-charge conversion process governed by the interplay between spin splitting and spin Hall effects: a longitudinal electric field induces transverse drift spin currents, which induce significant spin accumulation at the boundaries, generating a diffusive spin current that is converted back into a longitudinal charge current. By switching the Néel vector, a substantial change in magnetoresistance, akin to giant magnetoresistance in ferromagnets, is realized, enabling an electrically readable altermagnetic memory. Our microscopic theory provides deeper insights into the fundamental physics of the magnetoresistance effect in altermagnets and offers valuable guidance for designing next-generation ultradense and ultrafast spintronic devices based on altermagnetism.

We introduce the notion of the mixed state projected ensemble (MSPE), a collection of mixed states describing a local region of a quantum many-body system, conditioned upon measurements of the complementary region which are incomplete. This constitutes a generalization of the pure state projected ensemble in which measurements are assumed ideal and complete, and which has been shown to tend towards limiting pure state distributions depending only on symmetries of the system, thus representing a new kind of universality in quantum equilibration dubbed deep thermalization. We study the MSPE generated by solvable $(1+1)\mathrm{d}$ dual-unitary quantum circuit evolution, and identify the limiting mixed state distributions which emerge at late times depending on the size of the incomplete measurement, which we assume to be lossy, finding that they correspond to certain random density matrix ensembles known in the literature. We also derive the rate of the emergence of such universality. Furthermore, we investigate the quantum information properties of the states composing the ensemble, specifically their capacity to teleport quantum information between the ends of the system. The teleportation fidelity is upper bounded by the quantum conditional entropy, which we find exhibits a sharp transition from zero to maximal when the number of measurements lost matches of that the number of degrees of freedom to be teleported. Our results initiate the first investigation of deep thermalization for mixed state ensembles, relevant for present-day quantum simulation experiments wherein measurements are typically not perfect, and also amount to a physical and natural way of sampling from hitherto abstract random density matrix ensembles.

We test the isotropy of Hubble expansion by combining several probes for the first time, constructing full-sky maps of expansion rate variation using Type Ia supernovae, fundamental plane galaxies, and cosmic microwave background (CMB) temperature fluctuations. We find no hint of anisotropy or correlation between early- and late-Universe expansion across all systematic models. The 99% confidence upper limits on expansion rate anisotropy are 0.39% for low-redshift supernovae, 0.95% for high-redshift CMB, and 0.37% when combined at a 60-degree smoothing scale. A significant anomaly in the fundamental plane residual map may reflect systematics in the current dark energy spectroscopic instrument dataset, as evidenced by the absence of cross-correlation with other tracers and its correlation with spatial density variations.

We argue that the special extremal slice inside an AdS black hole is dual to an absolutely maximally entangled (AME) state. We demonstrate this by confirming the $n$-independence of holographic $n$th Renyi entropies for any bipartite subsystems. Our result gives an AME state in an infinite-volume system, where the local bond dimension is set by the black hole entropy. In particular, our construction provides concrete support from the gravity side for the emergence of random structures and an infinite-dimensional Hilbert space in recent nonisometric holographic codes.

We have made improved measurements of three-flavor neutrino mixing with $19.7(16.3)\times {10}^{20}$ protons on target in (anti-)neutrino-enhanced beam modes. A new sample of muon-neutrino events with tagged pions has been added at the far detector, as well as new proton and photon-tagged samples at the near detector. Significant improvements have been made to the flux and neutrino interaction modeling. T2K data continue to prefer the normal mass ordering and upper octant of ${\sin }^2{\theta }_{23}$ with a near-maximal value of the charge-parity violating phase with best-fit values in the normal ordering of ${\delta }_{\mathrm{CP}}=-{2.18}_{-0.47}^{+1.22}$, ${\sin }^2{\theta }_{23}={0.559}_{-0.078}^{+0.018}$ and $\mathrm{\Delta }{m}_{32}^2=({+2.506}_{-0.052}^{+0.039})\times {10}^{-3}{\mathrm{eV}}^2$.

We present a search for neutrinoless double-beta ($0\nu \beta \beta$) decay of ${}^{136}\mathrm{Xe}$ using the full KamLAND-Zen 800 dataset with 745 kg of enriched xenon, corresponding to an exposure of 2.1 ton yr of ${}^{136}\mathrm{Xe}$. This updated search benefits from a more than twofold increase in exposure, recovery of photo-sensor gain, and reduced background from muon-induced spallation of xenon. Combining with the search in the previous KamLAND-Zen phase, we obtain a lower limit for the $0\nu \beta \beta$ decay halflife of $T_{1/2}^{0\nu }>3.8\times {10}^{26}\mathrm{yr}$ at 90% CL, a factor of 1.7 improvement over the previous limit. The corresponding upper limits on the effective Majorana neutrino mass are in the range 28–122 meV using phenomenological nuclear matrix element calculations.

Quantum geometry has been shown to make an important contribution to the superfluid stiffness of flatband superconductors including moiré materials. In this Letter we use mean-field theory to derive an expression for the superfluid stiffness of time-reversal symmetric superconductors at zero temperature by computing the energy of the mean-field ground state as a function of pairing momentum. We show that the quantum geometric contribution to superfluid stiffness is a consequence of broken Galilean invariance in the interaction Hamiltonian, arising from momentum-dependent form factors related to the momentum dependence of Bloch states. The effects of broken Galilean invariance are not fully parametrized by the quantum metric considered in previous work. We obtain general lower and upper bounds that apply to both continuum and lattice models and present numerical calculations of the precise value in several important cases. The lower bound that we obtain is saturated by systems with Landau-level form factors and closely approximates the precise mean-field stiffness in all examples that we consider. Our results clarify the physical origin of the geometric contribution to superfluid stiffness and provide a new perspective on quantum geometry effects in interacting electron systems.

The emergence of hydrodynamic bend instabilities in ordered suspensions of active particles is widely observed across diverse living and synthetic systems, and is considered to be governed by dipolar active stresses generated by the self-propelled particles. Here, using linear stability analyses and numerical simulations, we show that a hydrodynamic bend instability can emerge in the absence of any dipolar active stress and solely due to the self-propulsion force acting on polar active units suspended in an incompressible fluid confined to a substrate. Specifically, we show analytically, and confirm in simulations, that a uniformly ordered state develops bend instability above a critical self-propulsion force. Numerical simulations show that a further increase in the self-propulsion strength leads the system towards a disorderly flow state. The results offer a new route for development of hydrodynamic instabilities in two-dimensional self-propelled materials that are in contact with a substrate, with wide implications in layers of orientationally ordered cells and synthetic active particles.

We introduce a dissipative lattice gauge model that exhibits the many-body version of the non-Hermitian skin effect. The dissipative couplings between dynamical gauge fields on the lattice links and the surrounding environment generate chiral motions of particles residing on lattice sites. Despite the complexity arising from many-body interactions, the local gauge symmetry enables the exact construction of a steady state that displays the many-body non-Hermitian skin effect. Furthermore, our approach can be generalized to realize a new type of many-body non-Hermitian skin effect, dubbed the hierarchical skin effect, where different subsystem degrees of freedom exhibit boundary accumulation of multiple moments at different orders. Our findings can be readily observed by engineering dissipation in state-of-the-art lattice gauge simulators.

We study the multiparameter sensitivity bounds of a network of $d$ spatially distributed Mach-Zehnder interferometers (MZIs). A generic single nonclassical state is mixed with $d-1$ vacuums to create a $d$-mode entangled state, each mode entering one input port of a MZI, while a coherent state enters its second port. We show that local measurements, independently performed on each MZI, are sufficient to provide a sensitivity saturating the quantum Cramér-Rao bound. The sensor network can overcome the shot noise limit for the estimation of arbitrary linear combinations of the $d$ phase shifts, provided that the nonclassical probe state has an antisqueezed quadrature variance. We compare the sensitivity bounds of this sensor with that achievable with $d$ independent MZIs, each probed with a nonclassical state and a coherent state. We find that the $d$ independent interferometers can achieve the same sensitivity of the entangled protocol, but at the cost of using $d$ nonclassical states rather than a single one. Considering the same average number of particles per shot in the two protocols, ${\overline{n}}_T$, we find analytically a sensitivity scaling $1/{\overline{n}}_T^2$ for the entangled case that provides a gain factor $d$ with respect to the separable case where the sensitivity scales as $d/{\overline{n}}_T^2$. We have numerical evidence that the gain factor $d$ is also found when fixing the total average number of particles, namely when optimizing with respect to the number of repeated measurements.

Controlling the synchronization of photons from probabilistic quantum sources plays a pivotal role in advancing efficient quantum information processing. We report the realization of a probabilistic entangling gate operating on actively synchronized photon pairs, using a quantum memory based on warm atomic vapor. We achieve a truth-table fidelity exceeding 85% and demonstrate Bell-inequality violation for all four Bell states. The reduction in visibility of the Hong-Ou-Mandel interference introduced by the storage process is identified as a primary factor limiting the gate fidelity. We derive an exact quantitative relation between Hong-Ou-Mandel visibility and gate fidelity for pure single photons, which applies to all photonic gates relying on interference, regardless of the physical platform.

This work reveals a fundamental link between general covariance and Birkhoff’s theorem. We extend Birkhoff’s theorem from general relativity to a broad class of generally covariant gravity theories formulated in the Hamiltonian framework. Conversely, we show that each one-parameter family of static, spherically symmetric spacetimes determines a class of covariant theories, each of which has that family of spacetimes as its entire vacuum solution space. Our systematic and model-independent framework applies to a wide range of spacetimes, including observationally inferred, quantum-gravity-inspired, and regular black holes. It provides a universal tool for probing their dynamical origins and enables the reconstruction of the underlying covariant theories from observational data, including gravitational-wave and black-hole-shadow measurements.

Álvarez-Domínguez et al. [Phys. Rev. Lett. 133, 041401 (2024)] have suggested that “it is not possible to concentrate enough light to precipitate the formation of an event horizon. We argue that the dissipative quantum effects coming from the self-interaction of light (such as vacuum polarization) are enough to prevent any meaningful buildup of energy that could create a black hole in any realistic scenario,” and “the dissipation of energy via Schwinger effect alone is enough to prevent the formation of kugelblitze with radii ranging from ${10}^{-29}$ to ${10}^8\mathrm{m}$.” I agree that, with the very restrictive assumption of Álvarez-Domínguez et al. of an adiabatic influx of electromagnetic energy, it is indeed highly implausible that black holes will form mainly from light in our actual Universe, either naturally or by any foreseeable human activity. However, if instead a rapidly changing influx is allowed, there are many idealized theoretical processes (though probably not occurring naturally or possible for humans to engineer) for forming black holes of any size down to near the Planck length (about ${10}^{-35}\mathrm{m}$) purely from photons, such as from colliding approximately plane-wave pulses, with only a small fraction of the energy escaping the black hole as scattered light or electron-positron pairs.

The STAR experiment reports new, high-precision measurements of the transverse single-spin asymmetries for ${\pi }^{\pm }$ within jets, namely the Collins asymmetries, from transversely polarized $p^{\uparrow }p$ collisions at $\sqrt{s}=510\mathrm{GeV}$. The energy-scaled distribution of jet transverse momentum, $x_{\mathrm{T}}=2p_{\mathrm{T},\text{jet}}/\sqrt{s}$, shows a remarkable consistency for Collins asymmetries of ${\pi }^{\pm }$ in jets between $\sqrt{s}=200\mathrm{GeV}$ and 510 GeV. This indicates that the Collins asymmetries are nearly energy independent, with, at most, a very weak scale dependence in $p^{\uparrow }p$ collisions. These results extend to high-momentum scales ($Q^2\le 3400{\mathrm{GeV}}^2$) and enable unique tests of evolution and universality in the transverse-momentum-dependent formalism, thus providing important constraints for the Collins fragmentation functions.

Phonons in solid-state quantum emitters play a crucial role in their performance as photon sources in quantum technology. For resonant driving, phonons dampen the Rabi oscillations, resulting in reduced state-preparation fidelities. The phonon spectral density, which quantifies the strength of the carrier-phonon interaction, is nonmonotonic as a function of energy. As one of the most prominent consequences, this should lead to the reappearance of Rabi rotations for increasing pulse power, according to the theoretical predictions in Vagov et al. [Phys. Rev. Lett. 98, 227403 (2007)]. In this Letter, we present the experimental demonstration of the reappearance of Rabi rotations for a resonantly driven quantum dot.

Excitons, bound electron-hole states, often dominate the optical response of two-dimensional (2D) materials and reflect their inherent properties, including spin-orbit coupling, magnetic ordering, or band topology. By focusing on a growing class of collinear antiferromagnets with a nonrelativistic spin splitting, referred to also as altermagnets (AMs), we propose a theoretical framework based on the spin space group to elucidate their resulting excitons. Our approach is illustrated on 2D AMs with spin-polarized valleys, where we classify the combination of conduction and valence bands by the spin space group representations into two cases that hosts bright $s$-like and $p$-like excitons, respectively. This analysis is further supported by effective Hamiltonians and the Bethe-Salpeter equation. We identify the excitonic optical selection rules from the calculated absorption spectra and the symmetry of bright excitons from their momentum-space envelope functions. Together with first-principles calculations, several material candidates are predicted for realizing excitons in 2D AMs. Our framework provides optical fingerprints for various cases of AMs, while their tunability, such as the strain-induced valley splitting, is also transferred to excitons allowing, additionally, valley-polarized photocurrent generation.

Developing telecom-compatible spin-photon interfaces is essential towards scalable quantum networks. Erbium ions (${\mathrm{Er}}^{3+}$) exhibit a unique combination of a telecom ($1.5\mathrm{\mu }\mathrm{m}$) optical transition and an effective spin-$1/2$ ground state, but identifying a host that enables heterogeneous device integration while preserving long optical and spin coherence remains an open challenge. We explore the potential of ${\mathrm{Er}}^{3+}:{\mathrm{CeO}}_2$ films on silicon and study the ${\mathrm{Er}}^{3+}$ spin coherence, offering low nuclear spin density and the potential for on-chip integration. We demonstrate a $38.8\mathrm{\mu }\mathrm{s}$ spin coherence, which can be extended to $176.4\mathrm{\mu }\mathrm{s}$ with dynamical decoupling. Pairing experiments with cluster correlation expansion calculations, we identify spectral diffusion induced by bath ${\mathrm{Er}}^{3+}$ spin flip-flops as the dominant decoherence mechanism and provide pathways to millisecond-scale coherence.

Irradiation of gallium arsenide (GaAs) produces immobile vacancies and mobile interstitials. Yet, after decades of experimental investigation, the immobile Ga vacancy continues to evade detection, raising the question: where is the Ga vacancy? Static first-principles calculations predict a Ga vacancy should be readily observed. We find that short-time dynamical evolution of primary defects is the key to explaining this conundrum. Using a dynamical multiscale atomistically informed device engineering (AIDE) method, we discover that during the initial displacement damage, the Ga vacancy (3-/2-) defect level pins the Fermi level near the midgap, producing oppositely charged vacancies and interstitials. Driven by Coulomb attraction, fast As interstitials preferentially annihilate Ga vacancies. The Ga vacancy population plummets below detectable limits—and the now unpinned Fermi level recovers—before being experimentally observed. This dynamical model solves the mystery of the missing Ga vacancy and reveals the importance of a multiscale approach to explore the dynamical chemical behavior in experimentally inaccessible short-time regimes.

Understanding chirality transfer from the molecular to the macroscopic scale poses a significant challenge in soft and biological condensed matter physics. Many nanorods of biological origin not only have chiral molecular features but also exhibit a spread in contour length leading to considerable size dispersity. On top of this, random backbone fluctuations are ubiquitous for nonrigid particles but their role in chirality transfer remains difficult to disentangle from that of their native chirality imparted by their effective shape or surface architecture. We report spontaneous entropy-driven chiral symmetry breaking from molecular simulations of cholesteric liquid crystals formed from achiral bead-spring rods with a continuous spread in contour length and marginal chain bending. The symmetry breaking is caused by long-lived chiral conformations of long rods undergoing chiral synchronization leading to a homochiral twisted nematic. A simple theory demonstrates that even without chiral synchronization, the presence of shape-persistent configurational fluctuations of nonchiral objects with inherent size dispersity can be harnessed to bootstrap chiral synchronization.