We demonstrate a blue-detuned magneto-optical trap (MOT) of a polyatomic molecule, calcium monohydroxide (CaOH). We identify a novel MOT frequency configuration that produces high spatial compression of the molecular cloud. This high compression MOT achieves a cloud radius of $59(5)\mathrm{\mu }\mathrm{m}$ and a peak density of $8(2)\times {10}^8{\mathrm{cm}}^{-3}$. We experimentally compare several blue-detuned MOT schemes for CaOH and find good agreement between our data and Monte Carlo simulations.

Alfvén waves, a fundamental mode of magnetized plasmas, are ubiquitous in space and laboratory plasmas. The nonlinear behavior of these modes is thought to play a key role in important problems in space plasma, such as the heating of the solar corona and solar wind turbulence. In particular, theoretical predictions show that these Alfvén waves may be unstable to various parametric instabilities, but space observations of these processes are limited. We demonstrate the first measurement of the Alfvén wave parametric decay instability (PDI) growth rate. Experiments are conducted on the Large Plasma Device at UCLA in which a high amplitude $\delta B/B_0\sim 0.7\%$ pump Alfvén wave is launched from one end of the device and a smaller seed Alfvén wave is launched from the other side. When the frequency of the seed wave is chosen to match the backward wave expected from PDI, damping of the seed wave is reduced. We compare this reduction in damping to the theoretically expected PDI growth rate while accounting for acoustic mode damping. Results show agreement between measurements and theoretical predictions. This not only provides critical validation for PDI theories and simulations that could help interpret future space observations but also suggests a new way of studying similar nonlinear wave phenomena.

Photonic crystals are artificial structures with periodic geometries that manipulate light at the wavelength scale. Recently, they have garnered significant attention in the field of topological photonics, where advanced band manipulation is explored to achieve breakthroughs in topological device applications. Conventional photonic crystals predominantly rely on a single spatial domain, characterized by spatially distributed dielectric modulation or metallic resonance. However, the degrees of freedom offered by spatial domains are often overlooked. Here, we theoretically propose and experimentally demonstrate photonic metacrystals that manipulate electromagnetic waves via minimal surfaces in three-dimensional space. These minimal surfaces partition the three-dimensional space into two complementary yet dual subspaces, each supporting a chiral topological semimetal. This spatial duality induces double-band degeneracy, analogous to the well-known time-reversal Kramers degeneracy, which has long been sought in classical systems. Previous proposals either relied on unrealizable strict symmetries or achieved double degeneracy only along high-symmetry lines. In contrast, we demonstrate that our double degeneracy exists globally, akin to the intrinsic spin degree of freedom of electrons. Furthermore, we extend the zero-frequency sixfold degeneracy of Maxwell’s equations to a nonzero frequency range, which significantly facilitates the characterization of the intrinsic topological properties. Our study provides new insights into the geometric foundations of topological physics.

Multiferroics, which combine ferroelectric and magnetic order, offer a transformative platform for next-generation electronic devices. However, the intrinsic competition between the mechanisms driving ferroelectricity and magnetism in single-phase materials severely limits their performance, typically resulting in weak magnetoelectric coupling at room temperature. Here, we propose a solution to this long-standing challenge through the novel concept of fractional quantum multiferroics (FQMF), where strong magnetoelectric coupling is naturally realized by coupling fractional quantum ferroelectricity with altermagnetism. Symmetry analysis shows that reversing the fractional quantum ferroelectricity polarization necessarily inverts the altermagnetic spin splitting under parity-time or time-reversal operations. A minimal tight-binding model reproduces this effect, demonstrating electrically driven spin control without rotating the Néel vector. First-principles calculations further identify a broad family of candidate materials in two and three dimensions, including bulk MnTe, ${\mathrm{Cr}}_2{\mathrm{S}}_3$, ${\mathrm{Mn}}_4{\mathrm{Bi}}_3{\mathrm{NO}}_{15}$ and two-dimensional ${\mathrm{AB}}_2$ bilayers such as ${\mathrm{MnX}}_2$ ($\mathrm{X}=\mathrm{Cl}$, Br, I), ${\mathrm{CoCl}}_2$, ${\mathrm{CoBr}}_2$, and ${\mathrm{FeI}}_2$. Notably, MnTe exhibits a high Néel temperature ($\sim 300\mathrm{K}$) and a large electrically switchable spin splitting ($\sim 0.8\mathrm{eV}$), demonstrating room-temperature magnetoelectric performance that surpasses that of conventional multiferroics. To further showcase the technological potential, we propose an electric-field-controlled FQMF tunnel junction based on MnTe that achieves tunneling magnetoresistance exceeding 300%. This Letter establishes FQMF as a distinct and promising route to achieving room-temperature robust electrically controlled magnetism, opening a new avenue for voltage-controlled spintronics.

We experimentally investigate the superfluid properties of a two-dimensional, weakly interacting Bose-Einstein condensate in the zero-temperature regime when it is subjected to a triangular optical lattice potential. We implement an original method, which involves solving the hydrodynamic continuity equation to extract the superfluid fraction tensor from the measured in situ density distribution of the fluid at rest. In parallel, we apply an independent dynamical approach that combines compressibility and sound velocity measurements to determine the superfluid fraction. Both methods yield consistent results in good agreement with simulations of the Gross-Pitaevskii equation as well as with the Leggett bounds determined from the measured density profiles.

Y-kapellasite [${\mathrm{Y}}_3{\mathrm{Cu}}_9{(\mathrm{OH})}_{19}{\mathrm{Cl}}_8$], which hosts an original anisotropic kagome sublattice, is a promising candidate for studying elusive and complex correlated physics. It exhibits a theoretically predicted in-plane $(1/3,1/3)$ magnetic order [Hering et al., npj Comput. Mater. 8, 1 (2022)], but its magnetic interaction values place it close to a phase boundary to a spin liquid state [Chatterjee et al., Phys. Rev. B 107, 125156 (2023)]. Our $\mathrm{\mu }\mathrm{SR}$ measurements under hydrostatic pressure demonstrate the complete suppression of static magnetism in favor of a fully dynamical ground state at 2.3 GPa. Complementary high-pressure x-ray and optical phonon measurements reveal a gradual reduction of the kagome anisotropy, enhancing magnetic frustration without structural transitions. Our results establish Y-kapellasite as a rare clean kagome model in which long-range order is suppressed by pressure-tuned frustration, the first fingerprint for the realization of a quantum spin liquid without strong disorder.

Dense bacterial suspensions at fluid interfaces provide a natural platform to explore active turbulence in a dimensional mismatch: active units are restricted to a two-dimensional surface, while the induced flows extend into the surrounding three-dimensional liquid. Using hydrophobic Serratia marcescens at the air-water interface, we realize interfacial bacterial turbulence as a distinct class of active turbulence. The system exhibits compressible in-plane flows, with the vortex size increasing with the thickness of the underlying fluid before saturating at a finite scale. This behavior contrasts sharply with bulk active turbulence, where correlation length typically scales with system size. Hydrodynamic theory, together with direct measurements of the three-dimensional flow field, shows that the coupling between interfacial and bulk flows sets the emergent length scale. Our results uncover the fundamental physics of interfacial bacterial turbulence and open new strategies for geometric control of collective active flows.

We report a measurement of the cosmic ray helium energy spectrum in the energy interval 0.16–13 PeV, derived by subtracting the proton spectrum from the light component (proton and helium) spectrum obtained with observations made by the Large High Altitude Air Shower Observatory (LHAASO) under a consistent energy scale. The helium spectrum shows a significant hardening centered at $E\simeq 1.1\mathrm{PeV}$, followed by a softening at $\sim 7\mathrm{PeV}$, indicating the appearance of a helium “knee.” Comparing the proton and helium spectra in the LHAASO energy range reveals some remarkable facts. In the lower part of this range, in contrast to the behavior at lower energies, the helium spectrum is significantly softer than the proton spectrum. This results in protons overtaking helium nuclei and becoming the largest cosmic ray component at $E\simeq 0.7\mathrm{PeV}$. A second crossing of the two spectra is observed at $E\simeq 5\mathrm{PeV}$, above the proton knee, when helium nuclei overtake protons to become the largest cosmic ray component again. These results have important implications for our understanding of the Galactic cosmic ray sources.

We report improved measurements of the all flavor astrophysical neutrino spectrum with IceCube by combining complementary neutrino samples in two independent analyses. Both analyses show evidence of a harder spectrum at energies below $\sim 30\mathrm{TeV}$ compared to higher energies where the spectrum is well characterized by a power law. The spectrum is better described by a log parabola or a broken power law, the latter being the preferred model. Both, however, reject a single power law over an energy range 5 TeV–10 PeV with a significance $>4\sigma$, providing new constraints on properties of cosmic neutrino sources.

Recent studies have drawn growing attention on nonrelativistic odd-parity magnetism in the wake of altermagnets. Nevertheless, odd-parity spin splitting is often believed to appear in noncollinear magnetic configurations. Here, using symmetry arguments and effective model analysis, we show that Floquet engineering offers a universal strategy for achieving odd-parity magnetism in two-dimensional (2D) collinear antiferromagnetism under irradiation of periodic driving light fields such as circularly polarized light, elliptically polarized light, and bicircular light. The symmetry requirements and three distinct lattice models of potential candidates are established. Strikingly, the light-induced odd-parity spin splitting can be flexibly controlled by adjusting the crystalline symmetry or the polarization state of incident light, enabling the reversal or conversion of spin splitting. By combining first-principles calculations and Floquet theorem, we present illustrative examples of 2D collinear antiferromagnetic (AFM) materials to verify the light-induced odd-parity magnetism. Our Letter not only offers a powerful approach for uniquely achieving odd-parity spin splitting with high tunability, but also expands the potential of Floquet engineering in designing unconventional compensated magnetism.

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 $T=0$.