Magnon-phonon hybridization in ordered materials is a crucial phenomenon with significant implications for spintronics, magnonics, and quantum materials research. We present direct experimental evidence and theoretical insights into magnon-phonon coupling in ${\mathrm{Mn}}_3\mathrm{Ge}$, a kagome antiferromagnet with noncollinear spin order. Using inelastic x-ray scattering and ab initio modeling, we uncover strong hybridization between planar spin fluctuations and transverse optical phonons, resulting in a large hybridization gap of $\sim 2\mathrm{meV}$. This coupling is driven by interlayer Heisenberg exchange interactions and is enhanced by the material’s symmetry and magnetic frustration. The simplicity of the ${\mathrm{Mn}}_3\mathrm{Ge}$ structure enables clear identification of the hybridized modes, bridging theoretical predictions and experimental observations. Our findings establish ${\mathrm{Mn}}_3\mathrm{Ge}$ as a model system for exploring magnon-phonon interactions and offer a pathway for designing materials with tunable magnetoelastic properties.

We present the first results from the Quantum Resolution-Optimized Cryogenic Observatory for Dark matter Incident at Low Energy (QROCODILE). The QROCODILE experiment uses a microwire-based superconducting nanowire single-photon detector (SNSPD) as a target and sensor for dark matter scattering and absorption, and is sensitive to energy deposits as low as 0.11 eV. We introduce the experimental configuration and report new world-leading constraints on the interactions of sub-MeV dark matter particles with masses as low as 30 keV. The thin-layer geometry of the system provides anisotropy in the interaction rate, enabling directional sensitivity. In addition, we leverage the coupling between phonons and quasiparticles in the detector to simultaneously constrain interactions with both electrons and nucleons. We discuss the potential for improvements to both the energy threshold and effective volume of the experiment in the coming years.

We have observed the signatures of valence electron rearrangement in photoexcited ammonia using ultrafast hard x-ray scattering. Time-resolved x-ray scattering is a powerful tool for imaging structural dynamics in molecules because of the strong scattering from the core electrons localized near each nucleus. Such core-electron contributions generally dominate the differential scattering signal, masking any signatures of rearrangement in the chemically important valence electrons. Ammonia represents an exception to the typically high core-to-valence electron ratio. We measured 9.8 keV x-ray scattering from gas-phase deuterated ammonia following photoexcitation via a 200 nm pump pulse to the 3s Rydberg state. We observed changes in the recorded scattering patterns due to the initial photoexcitation and subsequent deuterium dissociation. Ab initio calculations confirm that the observed signal is sensitive to the rearrangement of the single photoexcited valence electron as well as the interplay between adiabatic and nonadiabatic dissociation channels. The use of ultrafast hard x-ray scattering to image the structural rearrangement of single valence electrons constitutes an important advance in tracking valence electronic structure in photoexcited atoms and molecules.

Matter waves have been observed in double-slit experiments with microscopic objects, such as atoms or molecules. The wave function describing the motion of these objects must extend over a distance comparable to the slit separation, much larger than the characteristic size of the objects. Preparing such states for more massive objects, such as mechanical oscillators, remains an outstanding challenge. Here we delocalize the quantum ground state of an optically levitated nanosphere by modulating the stiffness of the confining potential. We show a more than threefold increase of the initial coherence length, which corresponds to mechanical momentum squeezing of more than 7 dB. Our work is a stepping stone toward the generation of coherence lengths comparable to the object size, a crucial regime for macroscopic quantum experiments.

Magnetic heat capacity measurements of a high-quality single crystal of the dipole-octupole pyrochlore ${\mathrm{Ce}}_2{\text{Hf}}_2{\mathrm{O}}_7$ down to a temperature of $T=0.02\mathrm{K}$ are reported. These show a two-peaked structure, with a Schottky-like peak at $T_1\sim 0.065\mathrm{K}$, similar to what is observed in its sister Ce pyrochlores ${\mathrm{Ce}}_2{\text{Zr}}_2{\mathrm{O}}_7$ and ${\mathrm{Ce}}_2{\text{Sn}}_2{\mathrm{O}}_7$. However, a second sharper peak is observed at $T_2\sim 0.025\mathrm{K}$, signifying the entrance to the ground state. The ground state appears to have gapped excitations, as even the most abrupt extrapolation to $C_P=0$ at $T=0\mathrm{K}$ fully accounts for the $R\ln (2)$ entropy associated with the pseudospin-$1/2$ doublet for ${\mathrm{Ce}}^{3+}$ in this environment. The ground state could be conventionally ordered, although theory predicts a much larger anomaly in $C_P$ at much higher temperatures than the measured $T_2$ for expectations from an all-in, all-out ground state of the XYZ Hamiltonian for ${\mathrm{Ce}}_2{\text{Hf}}_2{\mathrm{O}}_7$. The sharp low-temperature peak could also signify a crossover from a classical spin liquid to a quantum spin liquid (QSL). For both scenarios, comparison of the measured $C_P$ with NLC calculations suggests that weak interactions beyond the nearest-neighbor XYZ Hamiltonian become relevant below $T\sim 0.25\mathrm{K}$. The diffuse magnetic neutron scattering observed from ${\mathrm{Ce}}_2{\text{Hf}}_2{\mathrm{O}}_7$ at low temperatures between $T_2$ and $T_1$ resembles that observed from ${\mathrm{Ce}}_2{\text{Zr}}_2{\mathrm{O}}_7$, which is well established as a $\pi$-flux quantum spin ice (QSI). Together with the peak in the heat capacity at $T_2$, this diffuse scattering from ${\mathrm{Ce}}_2{\text{Hf}}_2{\mathrm{O}}_7$ is suggestive of a classical spin liquid regime above $T_2$ that is distinct from the zero-entropy quantum ground state below $T_2$.

Self-propulsion plays a crucial role in biological processes and nanorobotics, enabling small systems to move autonomously in noisy environments. Here, we theoretically demonstrate that a bound skyrmion-skyrmion pair in a synthetic antiferromagnetic bilayer can function as a self-propelled topological object, reaching speeds of up to a hundred million body lengths per second—far exceeding those of any known synthetic or biological self-propelled particles. The propulsion mechanism is triggered by the excitation of back-and-forth relative motion of the skyrmions, which generates nonreciprocal gyrotropic forces, driving the skyrmion pair in a direction perpendicular to their bond. Remarkably, thermal noise induces spontaneous reorientations of the pair and momentary reversals of the propulsion, mimicking behaviors observed in motile bacteria and microalgae.

Coupling with a resonant optical cavity is well known to modify the coherence of molecular vibrations. However, in the case of molecules coupled to a plasmonic nanocavity mode, the local mechanisms of vibrational coherence decay remain unclear. Here, the dynamics of a few hundred molecules of nitrothiophenol (NTP) within a single plasmonic nanocavity are studied by sum-frequency generation. Time-resolved experiments reveal a coherence lifetime sensitive to intermolecular dipole coupling strength, and is found to compete with cavity-induced vibrational dephasing above a threshold $\sim 10{\mathrm{cm}}^{-1}$. Tuning of the system dipole strength presents a quantitative means to explore the energy landscape of coherent interactions within nanoscale vibrational platforms, relevant for studies from vibrational chemistry to cavity quantum optomechanics.

Single crystal x-ray diffraction measurements have been carried out on epsilon oxygen up to 30 GPa to examine the behavior of the constituent $({\mathrm{O}}_2{)}_4$ units. An isostructural phase transition is evidenced by lattice parameter and intracluster (${\mathrm{O}}_8$) distance discontinuities and clear changes in the equation of state at $18.1\pm 0.5\mathrm{GPa}$ on compression. This transition corresponds well to the predicted collapse of the molecular magnetic moment from spin-liquid, ${\epsilon }_1$, to a spinless, ${\epsilon }_0$, states of the ${\mathrm{O}}_8$ structure. The collapse of the molecular magnetic moment has to date only been supported by spectroscopic data and, until now, has not been substantiated structurally.

Femtosecond laser excitation of nanometer thin heterostructures comprising a heavy metal and a magnetically ordered material is known to result in the emission of terahertz radiation. However, the nature of the emitted radiation from heavy metal/antiferromagnet heterostructures has sparked debates and controversies in the literature. Here, we unambiguously separate spin and charge contributions from Pt/NiO heterostructures by introducing an unprecedented methodology combining high external magnetic fields with a symmetry analysis of the emitted terahertz polarization. We observe two distinct mechanisms of terahertz emission, which we identify as optical difference frequency generation and ultrafast laser-induced quenching of the magnetization. We emphasize the absence of spin transport effects and signatures of coherent magnons. Overall, our Letter provides a general experimental methodology to separate spin and charge contributions to the laser-induced terahertz emission from heterostructures comprising a magnetically ordered material, thus holding great potential for advancing terahertz spintronics and establishing terahertz orbitronics.

Assembling increasingly larger-scale defect-free optical-tweezer-trapped atom arrays is essential for quantum computation and quantum simulations based on atoms. Here, we propose an AI-enabled, rapid, constant-time-overhead rearrangement protocol, and we experimentally assemble defect-free 2D and 3D atom arrays with up to 2024 atoms with a constant-time cost of 60 ms. The AI model calculates the holograms for real-time atom rearrangement. With precise controls over both position and phase, a high-speed spatial light modulator moves all the atoms simultaneously. This protocol can be readily used to generate defect-free arrays of tens of thousands of atoms with current technologies and become a useful toolbox for quantum error correction.

Chiral interactions within magnetic layers stabilize the formation of noncollinear spin textures, which can be leveraged to design devices with tailored magnetization dynamics. Here, we introduce chiral spin frustration in which energetically degenerate magnetic states frustrate the Dzyaloshinskii-Moriya interaction. We demonstrate magnon-driven switching of the chirally frustrated spin states in Bi-substituted yttrium iron garnet thin films. These states are defined by an in-plane macrospin neighboring two out-of-plane spins on either side with opposing chirality. Using scanning nitrogen-vacancy magnetometry and spin pumping, we identified four degenerate frustrated states and achieved their controllable switching via magnon spin torque. Crucially, the switching is unidirectional, with selectivity determined by the incoming magnon direction. This mechanism provides a powerful approach to manipulate frustrated spin states with magnons. Chiral spin frustration unlocks the geometry constraints of conventional frustration, and therefore opens new horizons for frustrated magnetism, paving the way for energy-efficient spintronic devices based on frustration.

Measurements of the EMC effect in the tritium and helium-3 mirror nuclei are reported. The data were obtained by the MARATHON Jefferson Lab experiment, which performed deep inelastic electron scattering from deuterium and the three-body nuclei, using a cryogenic gas target system and the high resolution spectrometers of the Hall A Facility of the Lab. The data cover the Bjorken $x$ range from 0.20 to 0.83, corresponding to a squared four-momentum transfer $Q^2$ range from 2.7 to $11.9(\mathrm{GeV}/c{)}^2$, and to an invariant mass $W$ of the final hadronic state greater than $1.84\mathrm{GeV}/c^2$. The tritium EMC effect measurement is the first of its kind. The MARATHON experimental results are compared to results from previous measurements by DESY-HERMES and JLab–Hall C experiments, as well as with few-body theoretical predictions.

The inelastic neutron scattering results and their analysis unequivocally point to a dominant Kitaev interaction in the honeycomb-lattice cobaltate ${\mathrm{BaCo}}_2({\mathrm{AsO}}_4{)}_2$. Our anisotropic-exchange model closely describes all available neutron scattering data in the material’s field-polarized phase. The density-matrix renormalization group results for our model are in close accord with the unusual double-zigzag magnetic order and the low in-plane saturation field of ${\mathrm{BaCo}}_2({\mathrm{AsO}}_4{)}_2$.

While ballistic electrons are a key tool for applications in sensing and flying qubits, sub-nanosecond propagation times and complicated interactions make control of ballistic single electrons challenging. Recent experiments have revealed Coulomb collisions of counterpropagating electrons in a beam splitter, giving time resolved control of interactions between single electrons. Here we use remote Coulomb interactions to demonstrate a scheme for sensing single ballistic electrons. We show that interactions are highly controllable via electron energy and emission timing. We use a weakly coupled “sensing” regime to characterize the nanoscale potential landscape of the beam splitter and the strength of the Coulomb interaction. We also show multielectron sensing with picosecond resolution.

Time-varying media break temporal translation symmetry, enabling advanced wave manipulation. However, this phenomenon remains largely unexplored in magnonic systems due to the challenge of achieving rapid and significant changes in magnon dispersion. Here, we construct a time-varying strong coupling between two magnon modes and observe chirped Rabi-like oscillations near the pulse edges. Developing a time-resolved frequency-comb spectroscopy technique, we characterize the frequency conversion of magnon modes induced by the time-varying strong-coupling effect. Moreover, we construct time slits with adjacent time interfaces and, for the first time, demonstrate the double-slit time diffraction of magnon modes, analogous to the well-known Young’s double-slit experiment. These findings rely solely on the time-varying strong coupling, independent of device reconfiguration. Our results open avenues for applications such as all-magnetic mixers or on-chip gigahertz sources.

We use the thermal effective theory to prove that, for the vacuum state in any conformal field theory in $d$ dimensions, the $n$th Rényi entropy $S_A^{(n)}$ behaves as $S_A^{(n)}=[f/(2\pi n{)}^{d-1}][\text{Area}(\partial A)/(d-2){\epsilon }^{d-2}](1+O(n))$ in the $n\to 0$ limit when the boundary of the entanglement domain $A$ is spherical with the UV cutoff $\epsilon$. The theory dependence is encapsulated in the cosmological constant $f$ in the thermal effective action. Using this result, we estimate the density of states for large eigenvalues of the modular Hamiltonian for the domain $A$. In two dimensions, we can use the hot spot idea, which describes the effective action in the high-temperature limit when the temperature is position-dependent, to derive more powerful formulas valid for arbitrary positive $n$. We discuss the difference between two and higher dimensions and clarify the applicability of the hot spot idea. We also use the thermal effective theory to derive an analog of the Cardy formula for boundary operators in higher dimensions.

Controlling the Stark perturbation from ambient thermal radiation is key to advancing the performance of many atomic frequency standards, including state-of-the-art optical lattice clocks (OLCs). We demonstrate a cryogenic OLC that utilizes a dynamically actuated radiation shield to control the perturbation at $1.7\times {10}^{-20}$ fractional frequency, a factor of $\sim 40$ beyond the best OLC to date. Our shield furnishes the atoms with a near-ideal cryogenic blackbody radiation (BBR) environment by rejecting external thermal radiation at the part-per-million level during clock spectroscopy, overcoming a key limitation with previous cryogenic BBR control solutions in OLCs. While the lowest BBR shift uncertainty is realized with cryogenic operation, we further exploit the radiation control that the shield offers over a wide range of temperatures to directly measure and verify the leading BBR Stark dynamic correction coefficient for ytterbium. This independent measurement reduces the literature-combined uncertainty of this coefficient by 30%, thus benefiting state-of-the-art Yb OLCs operated at room temperature. We verify the static BBR coefficient for Yb at the low ${10}^{-18}$ level.

We study particle acceleration in strongly turbulent pair plasmas using novel 3D particle-in-cell simulations, featuring particle injection from an external heat bath and diffusive escape. We demonstrate the formation of steady-state, nonthermal particle distributions with maximum energies reaching the Hillas limit. The steady state is characterized by the equilibration of plasma kinetic and magnetic pressures, which imposes upper limits on the acceleration rate. With growing cold plasma magnetization ${\sigma }_0$, nonthermal power-law spectra become harder, and the fraction of energy channeled into escaping cosmic rays increases. At ${\sigma }_0\gtrsim 1$, the escaping cosmic rays amount to more than 50% of the dissipated energy. Our method allows for kinetic studies of particle acceleration under steady-state conditions, with applications to a variety of astrophysical systems.

We present a conceptually simple and technically straightforward method for calculating photoelectron wave functions that is easily integrable with standard wave-function-based density-functional-theory packages. Our method is based on the Lippmann-Schwinger equation, naturally incorporating the boundary condition that the final photoelectron state must satisfy. The calculated results are in good agreement with the measured photon-energy and polarization dependence of the angle-resolved photoemission spectroscopy (ARPES) of graphene, the photon-energy-dependent evolution of the so-called dark corridor arising from the pseudospin, and ${\mathrm{WSe}}_2$, the circular dichroism reflecting the hidden orbital polarization. Our Letter opens doors to do-it-yourself simulations of ARPES with standard density-functional-theory packages, of crucial importance in the era of “quantum materials,” whose key experimental tool is ARPES.

Quantum information scrambling, which describes the propagation and effective loss of local information, is crucial for understanding the dynamics of quantum many-body systems. We report the observation of anomalous information scrambling in an atomic tweezer array with dominant van der Waals interaction. We characterize information spreading by an out-of-time-order correlator and observe persistent oscillations inside a suppressed linear light cone for the initial Néel state. Such an anomalous dynamic, which differs from both generic thermal and many-body localized scenarios, originates from weak ergodicity breaking in quantum many-body scarred systems.