We show that the amplitude of electromagnetic memory can be significantly enhanced in comparison to known estimates. In a Lorentz breaking phase of lowered phase velocity of light, there exist critical spacetime directions of memory-source emission along the effective light cone, about which the total memory offset receives order of magnitude increases. The same amplification is already present in the Lorentz preserving case by considering ultrarelativistic memory-source charges. These observations may pave the way for a first observation of the phenomenon of memory and laboratory tests of the concepts of asymptotic symmetries and soft theorems.

We use charge sensing to detect entropy changes in a double quantum dot defined by electrostatic gating of a GaAs/AlGaAs heterostructure. This system can be tuned to be two separate systems, like two independent, artificial atoms, or a single coherent system, like a molecule. We study entropy changes in both regimes due to changes in the occupation of the system. First, we recover the single-dot result for each dot, that the occupation of the dot by a single electron corresponds to an increase in the entropy of $k_{\mathrm{B}}\log 2$. Next, we examine two different charge transitions in the “molecular” regime and how it reveals itself in terms of the measured entropy. We also uncover a realization of Pauli blockade that clutters the entropy signal. By applying a rate equation model, we demonstrate the effect’s nonequilibrium origins and exclude it from the analysis of the system’s entropy. Understanding these experiments in this simplest coupled system enables the study of the entropy in other, more complicated coupled quantum systems, such as ones with topological or highly entangled ground states.

Frustration is a key driver of exotic quantum phases, yet its role in charge dynamics remains largely unexplored. We show that charge frustration—induced by electronic polarization effects—stabilizes unconventional insulating states in the one-dimensional extended Hubbard model. Using exact diagonalization and density-matrix renormalization group, we uncover a charge-disordered phase that remains insulating despite lacking long-range order and possessing an effectively attractive on-site interaction—a behavior reminiscent of gapful spin liquids in frustrated spin systems. We also identify a fragile ferroelectric phase and a charge-density-wave state with emergent eight-site periodicity. These findings establish charge frustration, driven by charge-dipole interactions, as a robust mechanism for realizing exotic phases in low-dimensional correlated systems, with implications for organic conductors, transition-metal oxides, and ultracold polar molecules.

The Thouless pump, a cornerstone of topological physics, enables unidirectional quantized wave or particle transport via geometric Berry phase engineering in periodically driven systems. While decades of research have been dedicated to monopole-mediated pumping, mechanisms governed by higher-order singularities like Berry dipoles remain unexplored. Here, we report on the experimental demonstration of a Berry-dipole-mediated returning Thouless pump (RTP) in a 1D acoustic waveguide array achieved through adiabatic encircling of a Berry dipole singularity. During this adiabatic cycle, an initial edge-localized mode first delocalizes into the bulk and eventually returns to the original edge, marking the characteristic signature of the RTP. Notably, this RTP exhibits an interesting feature of pseudospin flipping. The demonstrated RTP contrasts sharply with the well-studied monopole-governed pumps that feature unidirectional transport.

We report the creation of ultracold samples of ${{}^{39}\mathrm{K}}^{133}\mathrm{Cs}$ molecules in their rovibrational ground state. By investigating potentially suitable excited states using one- and two-photon spectroscopy, we have identified a pathway to the ground state via an exceptionally narrow intermediate state. Using stimulated Raman adiabatic passage, we create trapped samples of up to 3500 molecules at temperatures of $1\mathrm{\mu }\mathrm{K}$ with one-way efficiencies of 71%. The lifetime of these samples is limited by a near-universal two-body loss process, which could shed new light on similar loss mechanisms in other molecular species. Our results are a step toward establishing an alternative molecular species as a platform for the study of bosonic and fermionic quantum matter with strong dipolar interactions.

We present the first benchmark measurements of oxygen opacity at high-energy-density, crucial for understanding stellar interiors. A $3–5\text{−}\mathrm{\mu m}$ thick ${\text{SiO}}_2$ sample was heated using a Z facility x-ray source, and opacity was measured in the $5–19.5\AA$ range with multiple spectrometers. The electron temperature and density inferred from Si $K$-shell spectra were $148\pm 4\mathrm{eV}$ and $8.6\pm 1.4\times {10}^{21}{\mathrm{cm}}^{-3}$, respectively. Six experiments showed opacity reproducibility within $\pm 15\%$ and 5%–25% opacity uncertainty. Measured oxygen opacity and seven different opacity models exhibit extraordinary overall agreement. Discrepancies near the H-like photon ionization threshold and in certain spectral lines suggest the need for model refinements.

Conventional phase transitions in two-dimensional (2D) materials typically involve gradual and progressive structural evolution upon external stimuli. However, analogous to the latent heat phenomena in classical thermodynamics, where energy absorption leads to internal reconfiguration without immediate phase change, we report an unconventional “latent phase transition” in 2D palladium diselenide (${\mathrm{PdSe}}_2$), uncovered through in situ atomic scanning transmission electron microscopy. During Pd atom implantation and subsequent thermal annealing, the ${\mathrm{PdSe}}_2$ lattice absorbs input energy without significant structural rearrangement, maintaining its original framework over an extended temperature range. Remarkably, once a critical threshold of internal chemical pressure is reached, the structure abruptly collapses into a three-dimensional crystalline ${\mathrm{Pd}}_{17}{\mathrm{Se}}_{15}$ phase. Stabilized by the robust layer structure of ${\mathrm{PdSe}}_2$, this phase transition behavior closely mirrors the latent energy and sudden transformation characteristic of classical latent heat processes. Density functional theory calculations corroborate the mechanism, highlighting the role of van der Waals gap energy buffering and the weak $\mathrm{Pd}-\mathrm{Pd}$ interactions. Our findings establish an unusual phase transition paradigm in 2D materials, enriching the fundamental understanding of phase engineering in low-dimensional systems.

Controlling and monitoring interfacial chemical reactions is crucial for electrochemistry and photochemistry. Here, we developed a new type of interface-sensitive magnetic resonance technique by combining qPlus-based scanning probe microscopy (SPM) and quantum sensing based on a single nitrogen-vacancy center near the surface of a diamond. Using this technique, we investigated water dissociation at the hydrophilic diamond surface and monitored its elementary steps, including electron transfer, bond breaking, as well as water and hydrogen diffusion. The SPM tip was used to locally inject electrons into the interfacial water, and the resulting hydrated electrons (${\mathrm{e}}_{(\mathrm{aq})}^{-}$) were found to have specific configurations at the interface with a hyperfine interaction of about 28 MHz, which agrees with density-functional theory calculations. We observed that ${\mathrm{e}}_{(\mathrm{aq})}^{-}$ can induce water dissociation and the reaction product hydroxides diffuse $\sim 2.3$ times faster than water molecules. The diffusion coefficients of water and the reaction product hydroxides at the interface are about 3 orders of magnitude smaller than those in the bulk phase, but their ratio almost remain the same. These results show that the combination of SPM and quantum sensing provides a new platform to reveal the detailed electronic and nuclear processes of interfacial chemical reactions with nanometer resolution.

Optical atomic clocks with unrivaled precision and accuracy have advanced the frontier of precision measurement science and opened new avenues for exploring fundamental physics. A fundamental limitation on clock precision is the standard quantum limit (SQL), which stems from the uncorrelated projection noise of each atom. State-of-the-art optical lattice clocks interrogate large ensembles to minimize the SQL, but density-dependent frequency shifts pose challenges to scaling the atom number. The SQL can be surpassed, however, by leveraging entanglement, though it remains an open problem to achieve quantum advantage from spin squeezing at state-of-the-art stability levels. Here, we demonstrate clock performance beyond the SQL, achieving a fractional frequency precision of $1.1\times {10}^{-18}$ for a single spin-squeezed clock. With cavity-based quantum nondemolition measurements, we prepare two spin-squeezed ensembles of $\sim 30000$ strontium atoms confined in a two-dimensional optical lattice. A synchronous clock comparison with an interrogation time of 61 ms achieves a metrological improvement of 2.0(2) dB beyond the SQL, after correcting for state preparation and measurement errors. These results establish the most precise entanglement-enhanced clock to date and offer a powerful platform for exploring the interplay of gravity and quantum entanglement.

Gas bubble accumulation on substrates reduces the efficiency of many physicochemical processes, such as water electrolysis. For microbubbles, where buoyancy is negligible, coalescence-induced jumping driven by the release of surface energy provides an efficient pathway for their early detachment. At the nanoscale, however, gas compressibility breaks volume conservation during coalescence, suppressing surface energy release and seemingly disabling this detachment route. Using molecular dynamics simulations, continuum numerical simulations, and theoretical analysis, we show that surface nanobubbles with sufficiently large contact angles can nevertheless detach after coalescence. In this regime, detachment is powered by the release of pressure energy associated with nanobubble volume expansion. This finding thus establishes a unified driving mechanism for coalescence-induced bubble detachment across all length scales.

We introduce a new class of functional correlated disordered materials, termed gyromorphs, which uniquely combine liquidlike translational disorder with quasi-long-range rotational order, induced by a ring of $G$ delta peaks in their structure factor. We generate gyromorphs in 2D and 3D by spectral optimization methods, verifying that they display strong discrete rotational order but no long-range translational order, while maintaining rotational isotropy at short range for sufficiently large $G$. Using a coupled dipoles approximation, we numerically show that these structures outperform quasicrystals, stealthy hyperuniformity, and Vogel spirals in the formation of low-index-contrast isotropic band gaps in 2D, for both scalar and vector waves, and open complete isotropic band gaps in 3D. This claim is further supported by analytical effective-medium theory and by numerical estimates of scattering mean-free paths. Finally, we introduce “polygyromorphs” with several rotational symmetries at different length scales (i.e., multiple rings of delta peaks), enabling the formation of multiple band gaps in a single structure, thereby paving the way for fine control over optical properties.

X-ray magnetic circular dichroism provides a means to identify ferromagnetic, chiral, and altermagnetic orders via their time-reversal-symmetry ($\mathcal{T}$) breaking. However, the symmetry properties that govern circular dichroism (CD) in resonant inelastic x-ray scattering (RIXS) remain poorly understood. We show that, due to the inherent irreversibility of the RIXS process, RIXS-CD does not require $\mathcal{T}$ breaking to be present, but reflects the change in unitary symmetries associated with magnetic ordering. Using the altermagnetic MnTe as a model system, we observe an azimuthal-angle dependent RIXS-CD signal in the magnon excitations. Our findings highlight the sensitivity of RIXS-CD to the relativistic symmetry in magnetic systems and its potential application as a probe of magnetic domains.

We study the effects of an orbital magnetic field on the Mott metal-insulator transition in the Hubbard-Hofstadter model. We demonstrate that sufficiently large magnetic fields induce a Mott insulator-to-metal phase transition supporting our claim with dynamical mean field theory (DMFT) numerical results. For both competing phases (metal and insulator) we observe a magnetic-field-induced metallization reflected in an enhancement of kinetic and potential energy. The kinetic energy of the Mott insulator increases due to the Aharonov-Bohm effect experienced by electrons virtually tunneling around an elementary plaquette which is, however, suppressed by strong correlations. The kinetic energy of the metallic phase, on the other hand, is more strongly affected by the magnetic field through a field-driven redistribution of spectral weight due to the formation of magnetic minibands. This leads to an increase of the kinetic energy which tends to stabilize the metallic state. Our theoretical results might be relevant for recent experimental studies on magnetic field driven insulator-to-metal transitions in strongly correlated materials such as ${\mathrm{VO}}_2$, $\lambda$-type organic conductors, and moiré multilayers.

Altermagnets are a new class of magnetic materials that are promising for spintronics technology. Here, it is shown that in altermagnets, the circular dichroism (CD) in resonant photoelectron diffraction (RPED) contains a time-reversal odd signal, which provides a direct probe of the sublattice magnetization. RPED calculations are performed for MnTe at the Mn ${\mathrm{L}}_{2,3}$-edge resonance, using a combination of atomic multiplet and multiple scattering theory. A large magnetic CD is found for light helicity parallel to the Néel vector. This signal has the same angular distribution as the difference between the structural RPED of the two magnetic sublattices and its amplitude is approximately proportional to the x-ray magnetic CD in absorption of a single sublattice, thus providing a direct probe of the local magnetic moments.

Active fluids can develop spontaneous flow instabilities and complex patterns. However, spatiotemporal control of active particles has remained challenging, despite its relevance in biological and applied contexts. Here, we harnessed phototaxis to steer millions of swimming “puller” Chlamydomonas reinhardtii algae to create active jets and control both pearling and buckling instabilities through the preferential orientation of the cells. Our experiments, supported by a full analytical model and simulations, confirm long-standing predictions that self-generated flows can lead to jet destabilization. Our results further indicate that pullers can behave analogously to pushers when their orientation is properly tuned, and demonstrate how light enables the efficient control of active fluids.

Quantum mechanics suggests a persistent lattice vibration even at zero temperature; however, this elusive zero-point motion is difficult to measure for further analyses and exploitations. Here, we have performed near-resonant excitations on single perovskite ${\mathrm{CsPbI}}_3$ nanocrystals (NCs) at cryogenic temperatures, showing that pronounced up-converted photoluminescence (UC-PL) still takes place even at $\sim 4\mathrm{K}$ despite the vanishing phonon-assisted absorption. This surprising result can be explained in terms of a dynamic electric field caused by the zero-point motion of polar optical phonons, which gives rise to an absorption tail as in the Franz-Keldysh electroabsorption process. Furthermore, laser cooling is demonstrated in the $\sim 4\mathrm{K}$ UC-PL process of a single ${\mathrm{CsPbI}}_3$ NC, which opens a novel research avenue for the realization of even lower temperatures beyond the limit set forth by the helium-based cryostat.

Superconducting quantum computers leverage superconducting qubits, systems with well-defined energy levels, the spacing of which is determined by the properties of embedded Josephson junctions. Indeterminacy of Josephson junction manufacturing limits large-scale superconducting circuits; however, junction-by-junction tuning affords the possibility of an order of magnitude improvement of determinacy—although the origin of this tuning effect is uncertain. Understanding how tuning techniques may physically modify the tunnel barrier of a Josephson junction is important and will enable these techniques to be optimized. We develop a model of junction tuning based on depinning theory to interpret a phase diagram of the tuning rate. We extract the dependence on temperature, time-varying voltages, and oscillation frequency. Comparing the effect of junction tuning on room-temperature $I\text{−}V$’s, electrical breakdown, and frequency of higher-energy levels of transmon qubits indicates that the tuning process leaves the barrier thickness unchanged but modifies its composition.

Despite its tiny net magnetization, the antiferromagnetic (AFM) van der Waals material ${\mathrm{Co}}_{1/3}{\mathrm{NbS}}_2$ exhibits a large transverse Hall conductivity ${\sigma }_{xy}$ even at zero applied magnetic field, which arises, as recently shown, from the topological nature of its noncoplanar “tetrahedral” AFM order. This triple-$\mathbf{q}$ magnetic order can be regarded as the short-length-scale limit of a magnetic skyrmion lattice and has an intrinsic spin chirality. Here, we show, using optical wavelengths spanning the ultraviolet to infrared (400–1000 nm), that magnetic circular dichroism provides an incisive optical probe of the topological AFM order in ${\mathrm{Co}}_{1/3}{\mathrm{NbS}}_2$. Measurements as a continuous function of photon energy are directly compared with first-principles calculations, revealing the influence of the underlying quantum geometry on optical conductivity. Leveraging the power and flexibility of optical methods, we use scanning magnetic circular dichroism microscopy to directly image chiral AFM domains and demonstrate writing of chiral AFM domains.

Thermal Hall effect (THE) in insulators is a remarkable phenomenon that arises from the motion of chargeless quasiparticles under a magnetic field. While magnons or various exotic excitations were considered as the origin of THE in some magnetic materials, there is more and more evidence suggesting that phonons play a significant role. However, the mechanism behind phonon THE is still unknown. Here we report the observation of THE, including planar THE, in a broad range of nonmagnetic insulators and semiconductors: ${\mathrm{SrTiO}}_3$, ${\mathrm{SiO}}_2$ (quartz), MgO, ${\mathrm{MgAl}}_2{\mathrm{O}}_4$, Si, and Ge. While the presence of antiferrodistortive domains in ${\mathrm{SrTiO}}_3$ and chiral structure in ${\mathrm{SiO}}_2$ may complicate the interpretation of THE, the striking observations of THE in trivial insulators MgO and ${\mathrm{MgAl}}_2{\mathrm{O}}_4$, as well as in high-purity intrinsic semiconductors Si and Ge, demonstrate that phonon THE is a universal property of crystals. Without other effects on phonons such as from magnons, this universal phonon THE is characterized by a scaling behavior of $|{\kappa }_{xy}|\sim {\kappa }_{xx}^2$. Our results experimentally discover a fundamental physics of phonons in the magnetic field, which should come from the direct coupling between atom vibrations and the field. Starting from this universal phonon THE in crystals, previous interpretations of THE in magnetic or nonmagnetic materials need to be reconsidered.

Twisted magnetic van der Waals materials offer a promising route for multiferroic engineering, yet modeling large-scale moiré superlattices remains challenging. Leveraging a newly developed SpinGNN++ framework that effectively handles spin-lattice coupled systems, we develop a comprehensive interatomic machine learning potential and apply it to twisted bilayer ${\mathrm{NiI}}_2$. Structural relaxation introduces moiré-periodic “bumps” that modulate the interlayer spacing by about 0.55 Å and in-plane ionic shifts up to 0.48 Å. Concurrently, our machine learning potential, which faithfully captures all key spin interactions, produces reliable magnetic configurations; combined with the more accurate generalized Katsura-Nagaosa-Balatsky mechanism, it delivers precise spin-driven polarization. For twist angles $1.89°\le \theta \le 2.45°$, both mechanisms become prominent, yielding rich polarization textures that combine ionic out-of-plane dipoles with purely electronic in-plane domains. In the rigid (unrelaxed) bilayer, skyrmions are absent; lattice relaxation is thus essential for generating polar-magnetic topologies. In contrast, near $\theta \approx 60°$, stacking-dependent ferroelectric displacements dominate, giving rise to polar meron-antimeron networks. These results reveal cooperative ionic and spin-driven ferroelectricity in twisted bilayer ${\mathrm{NiI}}_2$, positioning twisted van der Waals magnets as adaptable platforms for tunable multiferroic devices.