Altermagnets, recently discovered unconventional magnets distinct from both ferro- and antiferromagnets, have rapidly emerged as a prominent research topic in condensed matter physics. Altermagnets are characterized by alternating collinear magnetic moments with zero net magnetization in real space, and spin splittings with even-parity symmetry in momentum space. However, their counterparts exhibiting odd-parity spin splittings are generally thought to be absent in collinear magnets. Here, we show that such unconventional odd-parity magnets can be induced from collinear antiferromagnets by symmetry engineering. Remarkably, using effective model analysis within a Floquet-theory framework, we demonstrate that circularly polarized light irradiation of conventional antiferromagnetic lattices breaks a spin-preserving pseudo-time-reversal symmetry and induces both $p$- and $f$-wave magnets, realizing novel magnetic states dubbed “Floquet odd-parity collinear magnets.” Moreover, we also uncover light-induced antiferromagnetic Chern insulating states in the $f$-wave magnets. The proposed Floquet odd-parity magnet is confirmed by first-principles calculations of ${\mathrm{MnPSe}}_3$ under circularly polarized light. Our Letter not only proposes a new class of unconventional magnets, but also opens an avenue for light-induced magnetic phenomena in spintronic applications.

We report Coulomb drag studies in an electron-hole bilayer graphene heterostructure in a magnetic field, where the orbital, spin, and valley degrees of freedom are lifted by the combined effects of exchange interaction, Zeeman energy, and a vertical displacement field. Our device enables the application of a large vertical displacement field across both layers. In addition to the well-established strong Coulomb drag between the Landau levels with an orbital quantum number $N=0$, we observe a Coulomb drag signal between the $N=1$ Landau levels under a suitable vertical displacement field. As the vertical displacement field increases further, the Coulomb drag signal between $N=1$ Landau levels weakens, and a Coulomb drag signal emerges between the $N=0$ and $N=1$ Landau levels. These findings suggest the important roles of the orbital index and the vertical displacement field in interlayer Coulomb interaction within the quantum Hall regime of coupled bilayer systems.

High-order interdependencies are central features of complex systems, yet a mechanistic explanation for their emergence remains elusive. Currently, it is unknown under what conditions high-order interdependencies, quantified by the information-theoretic construct of synergy, arise in systems governed by pairwise interactions. We solve this problem by providing precise sufficient and necessary conditions for when synergy prevails over low-order interdependencies in the weak interaction regime; namely, we prove that antibalanced (highly frustrated) correlational structures in Gaussian systems are sufficient for synergy dominance and that antibalanced interaction motifs in Ornstein-Uhlenbeck processes are necessary for synergy dominance. We validate the applicability of these analytical insights beyond the weak interaction regime, as well as in Ising, oscillatory, and empirical networks from multiple domains. Our results demonstrate that pairwise interactions can give rise to synergistic information in the absence of explicit high-order mechanisms, and highlight structural balance theory as an instrumental conceptual framework to study high-order interdependencies.

We report on the search for x-ray radiation as predicted from dynamical quantum collapse with low-energy electronic recoil data in the energy range of 1–140 keV from the first science run of the XENONnT dark matter detector. Spontaneous radiation is an unavoidable effect of dynamical collapse models, which were introduced as a possible solution to the long-standing measurement problem in quantum mechanics. The analysis utilizes a model that for the first time accounts for cancellation effects in the emitted spectrum, which arise in the x-ray range due to the opposing electron-proton charges in xenon atoms. New world-leading limits on the free parameters of the Markovian continuous spontaneous localization and Diósi-Penrose models are set, improving previous best constraints by two orders of magnitude and a factor of five, respectively. For the strength and correlation length of the continuous spontaneous localization model, values in the originally proposed parameter ranges are experimentally excluded for the first time.

In quantum networks, after passing through noisy channels or information processing, residual states may lack sufficient entanglement for further tasks, yet they may retain hidden quantum resources that can be recycled. Efficiently recycling these states to extract entanglement resources, such as genuine multipartite entanglement or Einstein-Podolsky-Rosen pairs, is essential for optimizing network performance. Here, we develop a tripartite entanglement distillation scheme using an eight-photon quantum platform, demonstrating entanglement superactivation phenomena which are unique to multipartite systems. We successfully generate a three-photon genuinely entangled state from two biseparable states via local operations and classical communication, demonstrating superactivation of genuine multipartite entanglement. Furthermore, we extend our scheme to generate a three-photon state capable of extracting an Einstein-Podolsky-Rosen pair from two initial states lacking this capability, revealing a previously unobserved entanglement superactivation phenomenon. Our methods and findings offer not only practical applications for quantum networks, but also lead to a deeper understanding of multipartite entanglement structures.

We present absolute frequency measurements of $2{\mathrm{S}}_{1/2}\text{−}\mathrm{n}{\mathrm{S}}_{1/2}$ two-photon transitions with $n=8$, 9, and 10 in a cryogenic beam of atomic hydrogen. Each transition has been measured with a fractional uncertainty of $\approx 2.6\times {10}^{-12}$. Combining the results from this Letter and the $1{\mathrm{S}}_{1/2}\text{−}2{\mathrm{S}}_{1/2}$ transition frequency, we extract a root-mean-square proton radius of $r_p=0.8433(31)\mathrm{fm}$ and a Rydberg frequency of $c{R}_{\infty }=3289841960252.9(9.7)\mathrm{kHz}$. These are in good agreement with the CODATA 2022 recommended values.

Squeezed states of light enable quantum-enhanced measurements but are limited by optical loss, particularly at $2\mathrm{\mu }\mathrm{m}$ where photodiode efficiency is low. We report the first loss-tolerant, audio-band squeezed light detection at 1984 nm by using a phase-sensitive amplifier to amplify the squeezed vacuum prior to detection. This technique increases the effective detection efficiency from 74% to 95% and increases the observed squeezing from 4 to 8 dB, the highest level of squeezing observation reported at this wavelength. Additionally, the vacuum to dark-noise clearance increases, extending the effective measurement bandwidth toward lower frequencies. This approach is largely wavelength independent, extending high-fidelity quantum measurements to future gravitational-wave detectors and related quantum technologies.

Quantum networks, which integrate multiple quantum computers and the channels connecting them, are crucial for distributed quantum information processing but remain inherently susceptible to channel noise. Channel purification emerges as a promising technique for suppressing noise in quantum channels without complex encoding and decoding operations, making it particularly suitable for remote quantum information transmission in optical systems. In this Letter, we introduce an experimental setup for efficient channel purification, harnessing the spatial and polarization properties of photons. Our design employs two Fredkin gates to enable coherent interference between independent noise channels, achieving effective noise suppression across a wide range of noise levels and types. Through application to entanglement distribution, channel purification demonstrates a strong capability to preserve entanglement under channel noise, suggesting that it can serve as a complementary and resource-efficient alternative to conventional entanglement purification in quantum network tasks.

We experimentally measure geostrophic turbulence in a rotating, differentially heated fluid annulus, which is bounded by convectively driven warm and cold flows at the outer and inner boundaries, respectively. The horizontal kinetic energy spectra exhibit a range at low wave number which scales as $k^{-3}$, where $k$ denotes the horizontal wave number, with spectral amplitude that correlates with the square of the Brunt-Väisälä frequency at the same heights as the velocity measurements. The observed turbulent state exhibits a forward enstrophy cascade across all scales along with bidirectional energy transfer, which is evidenced by a reversal in the sign of the spectral energy flux at a scale proportional to the internal Rossby radius of deformation. These findings highlight the role of baroclinic instability in shaping the distribution of energy across scales, with implications for synoptic-scale turbulent flows near Earth’s tropopause.

Despite extensive experimental and theoretical work over several decades, Schmid-Bulgadaev quantum phase transition remains a subject of debate. Here we revisit this problem by performing systematic experiments on low-frequency current-voltage characteristics of Josephson junctions over a wide range of parameters. The experiments are conducted in a true resistive environment formed by a metallic on-chip resistor located near the junction. Over the parameter range of the experiment, we find that the transition occurs when the resistance crosses the quantum value $h/(4e^2)\simeq 6.5\mathrm{k}\mathrm{\Omega }$ for Cooper pairs, as originally predicted. The temperature $T$ of the experiment is naturally nonzero, but our basic theoretical modeling corroborates that the observations under these conditions can serve as the basis for the conclusions made, in particular, the crossover resistance from superconducting to insulating regime is the same as that at $T=0$.

Hysteresis, with rich dynamical behaviors—especially in interacting systems—has drawn broad research interest. Yet its dynamic scalings across timescales lack a unified description, and their transitions remain unclear. Here, we study the stochastic ${\varphi }^4$ model driven periodically by an external field $H$. For large systems with small noise strength $\sigma$, we find the coercivity $H_c\equiv H(⟨\varphi ⟩=0)$ sequentially exhibits distinct behaviors with increasing driving rate $v_H$: $v_H$-scaling increase, stable plateau ($v_H^0$), $v_H^{1/2}$-scaling increase, and abrupt decline to disappearance. The plateau reflects the competition between thermodynamic and quasistatic limits, namely, ${\lim }_{\sigma \to 0}{\lim }_{v_H\to 0}{H}_c=0$, and ${\lim }_{v_H\to 0}{\lim }_{\sigma \to 0}{H}_c=H^{*}$. Here, $H^{*}$ is exactly the field-driven first-order phase transition point. In the post-plateau regime, $(H_c-H_P)$ scales with $(v_H-v_P{)}^{2/3}$ with $v_P$ and $H_P$ being the reference points of the plateau. Moreover, we reveal a finite-size scaling for the coercivity plateau as $v_P\sim {\sigma }^2$ and $(H^{*}-H_P)\sim {\sigma }^{4/3}$ by utilizing renormalization-group theory. Our Letter provides a panoramic view of finite-time scalings of the hysteresis and offers new insights into the interplay between finite-time and finite-size effects in nonequilibrium systems.

Understanding different aspects of time is at the core of many areas in theoretical physics. Minimal models of continuous stochastic and quantum clocks have been proposed to explore fundamental limitations on the performance of timekeeping devices. Owing to the level of complexity in the clock structure and its energy consumption, such devices show trade-offs whose characterization remains an open challenge. Indeed, even conceptual designs for thermodynamically efficient quantum clocks are not yet well understood. In condensed matter theory, time crystals were found as an exciting new phase of matter featuring oscillations in (pseudo) equilibrium with first experimental observations appearing recently. This naturally prompts the question: Can time crystals be used as quantum clocks, and what is their performance from a thermodynamic perspective? We answer this question and find that quantum time crystals are indeed genuine quantum clocks with a performance enhanced by the spontaneous breaking of time-translation symmetry.

Because they are likely to accrete substantial amounts of interstellar gas, merging supermassive binary black holes are expected to be strong multimessenger sources, radiating gravitational waves, photons from thermal gas, and photons from relativistic electrons energized by relativistic jets. Here we report on a numerical simulation that covers the late inspiral, merger, and initial postmerger phase of such a system where both black holes have the same mass and spin, and both spin axes are parallel to the orbital angular momentum. The simulation incorporates both 3D general relativistic magnetohydrodynamics and numerical relativity. The thermal photon power during the late inspiral, merger, and immediate postmerger phases is drawn from strong shocks rather than dissipation of turbulence inside a smoothly structured accretion disk as typically found around accreting single black holes. We find that the thermal photon and jet Poynting flux outputs are closely related in time, and we posit a mechanism that enforces this relation. The power radiated in both photons and jets diminishes gradually as merger is approached, but jumps sharply at merger to a noisy plateau. Such a distinct lightcurve should aid efforts to identify supermassive black hole mergers, with or without accompanying gravitational wave detections.

Superluminous supernovae (SLSNe) are a new class of transients with luminosities $\sim 10–100$ times larger than the usual core-collapse supernovae. Their origin is still unclear. One widely discussed scenario involves a millisecond magnetar central engine. The GeV-TeV emission of SLSNe has been predicted in the literature but has not been convincingly detected yet. Here, we report the results of the search for $\gamma$-ray emission in the direction of SN 2017egm, one of the closest SLSNe detected so far, using 15 years of Fermi-LAT Pass 8 data. There is a transient $\gamma$-ray source appearing about two months after this event and lasting a few months. Monte Carlo simulations show that the $\gamma$-ray signal has a global significance of at least $4\sigma$. Both the peak time and the luminosity of the GeV emission are consistent with the magnetar model prediction, suggesting that such a GeV transient is the high-energy counterpart of SN 2017egm and the central engine of this SLSNe is a young magnetar.

In 1996, Hatano and Nelson proposed a non-Hermitian lattice model containing an imaginary Peierls phase [Phys. Rev. Lett. 77, 570 (1996)], which subsequent analyses revealed to be an instance of a new class of topological systems. Here, we experimentally realize a continuum analog to this model containing an imaginary gauge potential using a homogeneous spin-orbit coupled Bose-Einstein condensate (BEC). Non-Hermiticity is introduced by adding tunable spin-dependent loss via microwave coupling to a subspace with spontaneous emission. We demonstrate that the resulting Heisenberg equations of motion for position and momentum depend explicitly on the system’s phase-space distribution. First, we observe collective nonreciprocal transport in real space, with a “self-acceleration” that decreases with the BEC’s spatial extent, consistent with non-Hermitian Gross-Pitaevskii simulations. We then examine localized edge states: the relatively strong interactions in our BEC suppress the formation of topological edge states, yielding instead highly excited states localized by an interplay between self-acceleration and wave function spreading. Finally, we confirm that our non-Hermitian description remains valid at all times by comparing it to a multilevel master equation treatment.

While THz pulses with durations close to a single oscillation period are widely regarded as optimal stimuli for achieving the fastest and most energy-efficient control of spins in magnetic materials, all-dielectric metasurfaces have recently been demonstrated to provide the least dissipative platform for enhancing and controlling light-spin coupling. All-dielectric metasurfaces for the THz control of spins hold great potential in the field of spintronics and related technologies, pushing the boundaries of speed and energy efficiency in spin-based information processing. Here, we introduce and demonstrate a novel material: a specially designed dielectric metasurface for an advanced THz control of spins in a ferrimagnetic film of iron garnet. By structuring a nonmagnetic substrate, one can force a THz electromagnetic field, otherwise described by plane waves, to acquire an out-of-plane magnetic field and thus enable arbitrary direction of the torque acting on spins in all three dimensions. Hence, metaphotonics opens up a plethora of opportunities for advanced control of spins at THz rates in many hot fields of contemporary science, including spintronics, magnonics, and quantum computing.

Entanglement is crucial for quantum networks and computation, yet maintaining high-fidelity entangled quantum states is hindered by decoherence and resource-intensive purification methods. Here, we experimentally demonstrate entanglement pumping, utilizing bosonic quantum error correction (QEC) codes as long-coherence-time storage qubits. By repetitively generating entanglement with short-coherence-time qubits and injecting it into error-detectable logical qubits, our approach effectively preserves entanglement. Through error-detection to discard error states and entanglement pumping to mitigate errors within the code space, we extend the existence time of entanglement by nearly 50% compared to the case without entanglement pumping. This entanglement pumping scheme can additionally serve as an erasure detection protocol for the dual-rail code. This Letter highlights the potential of bosonic logical qubits for scalable quantum networks and introduces a novel paradigm for efficient entanglement management.

Superconductivity can be destroyed by a magnetic field with an upper bound known as the Pauli limit. Here, we report a large violation of the Pauli limit in both in-plane and perpendicular magnetic fields in ${\mathrm{La}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{NiO}}_2$ infinite-layer superconducting thin films. The critical field $H_{\mathrm{c}2}$ shows a clear anisotropic behavior and a pronounced upturn at ultralow temperatures, manifesting anisotropic superconductor-metal transition features. Scaling analysis near the $\mathit{T}\to 0$ quantum critical point of this transition reveals a quantum Griffiths singularity arising from quenched disorder, hallmarked by a diverging dynamic critical exponent. These quantum Griffiths singularity induced quantum fluctuations provide the origin for the pronounced $H_{\mathrm{c}2}$ upturn and represent a key intrinsic mechanism for the robust violation of the Pauli limit. Our findings establish a microscopic mechanism where heavy-fermion mass renormalization suppresses orbital pair breaking, enabling disorder-enhanced quantum fluctuations to preserve superconductivity far beyond the Pauli limit.

We present Coulomb-drag measurements on a heterostructure comprising two Bernal-stacked bilayer graphene (BLG) sheets separated by a 2.5 nm hexagonal boron nitride (hBN) spacer in the quantum Hall (QH) regime. Using top and bottom gate control, together with an interlayer bias, we independently tune the two BLG layers into either the lowest ($N=0$) or second ($N=1$) Landau level (LL) orbital and probe their interlayer QH states. When both layers occupy the $N=0$ orbital, we observe both interlayer exciton condensates (ECs) at integer total filling and interlayer fractional QH states, echoing the results in double monolayer graphene. In contrast to previous studies, however, when both BLG layers occupy the $N=1$ orbital, we also observe quantized drag signals, signifying an interlayer exciton condensate formed between the second LLs. By tuning the layer degree of freedom, we find that this $N=1$ EC state arises only when the $N=1$ wave function in each BLG is polarized toward the hBN interface to maximize the interlayer Coulomb interaction.

Tungsten diboride (${\mathrm{WB}}_{2+x}$) has been predicted to be a superhard material. It, however, has yet to be practically realized, because of its intrinsically low toughness, without involving favorable dislocation slip systems. Here, we report a viable strategy to effectively strengthen both the toughness and hardness of ${\mathrm{WB}}_{2+x}$ by introducing ordered atomic vacancies to increase dislocation mobility along certain directions. By doping with rhenium atoms, the ordered metal-vacancy pairs are revealed to occur extensively in the optimally doped sample with a composition of ${({\mathrm{W}}_{0.9}{\mathrm{Re}}_{0.1})}_{1-\delta }{\mathrm{B}}_{2+x}$ synthesized under high pressure. Such vacancy pairs are found to mainly reside in the $\{210\}$ and $\{102\}$ planes, along which the long-range dislocations are kinetically favored for improving its toughness and plasticity to achieve a load-invariant superhardness of $\sim 40\mathrm{GPa}$. In addition, its thermal stability is drastically promoted and rivals that of cubic boron nitride ($c\mathrm{BN}$). These discoveries not only experimentally identify a superhard material but also provide powerful insights into how the mechanical properties of transition-metal diborides can be improved by tailoring atomic deficiencies.