Bound states in the continuum (BICs) are exotic optical topological singularities that defy the typical radiation within the continuum of radiative modes and carry topological polarization vortices in momentum space. Enabling ultrahigh quality factors, BICs have been applied in realizing lasing and Bose-Einstein condensation, and their momentum-space vortex topologies have been exploited in passive systems, revealing novel spin-orbit photonic effects. Here, we demonstrate the inherent spin-orbit locking in topological BIC lasing. Utilizing ${\mathrm{C}}_{4v}$ and ${\mathrm{C}}_{6v}$ photonic crystal slabs, we achieve distinct spin-orbit locking combinations in BIC lasing of $+1$ and $-2$ topological charges. Spin-orbit locking phenomena are directly observed by momentum-space spin-dependent self-interference patterns. Real-space spin separations, as a counterpart of the momentum-space spin-orbit locking, are also revealed. Our results reveal new spin-orbit locking phenomena in BIC lasing, presenting significant potential for advancements in topological photonic source applications.

A complete, kinetic description of electron-seeded strong-field QED showers in crossed electromagnetic fields is derived. The kinetic structure of the shower and its temporal evolution are shown to be a function of two parameters: the initial shower quantum parameter and radiation time. The latter determines the short and long time evolution of the shower. Explicit solutions for the shower multiplicity (number of pairs per seed electron) and the emitted photon spectrum are obtained for both timescales. Our approach is first derived considering showers in a constant, homogeneous magnetic field. We find that our results are valid for any crossed fields and we apply them to laboratory settings for which we obtain fully analytical, predictive scaling laws.

Despite the recent success of identifying experimental signatures of the orbital Hall effect (OHE), the research on the microscopic mechanisms behind this unique phenomenon is still in its infancy. Here, using a gapped 2D Dirac material as a model system of the OHE, we develop a microscopic theory of orbital transport which captures extrinsic disorder effects nonperturbatively. We show that it predicts several hitherto unknown effects, including (i) a strong dependence of the orbital Hall conductivity with the strength and symmetry of the impurity scattering potential, and (ii) a smooth crossover from intrinsic to extrinsic OHE as a function of the Fermi energy and impurity density. In contrast to previous (perturbative) studies, the OHE is found to exhibit bona fide diffusive behavior in the dilute impurity limit, which we trace back to the dominance of skew scattering–type processes. More generally, we argue that the newly unveiled orbital skew scattering mechanism governs the diffusive OHEs of a large class of 2D materials even when the crystal structure is inversion symmetric. Our work unveils the crucial nature of nonperturbative vertex corrections for a complete description of orbital transport and confirms common short-range impurities as key enablers of the OHE.

We propose to expand the territory of density functional theory to strongly correlated electrons by reformulating the Kohn-Sham scheme in the representation of fractionalized particles. We call it the “${\mathrm{KS}}^{*}$ scheme.” Using inhomogeneous $t-J$ chains as a test bed, we show that the ${\mathrm{KS}}^{*}$ scheme with simple local density approximation is able to achieve accurate ground-state energy and density distribution comparable to the density matrix renormalization group method, while the computational complexity is much lower.

The brain accounts for approximately 20% of metabolism and, as a result, generates protein waste which requires efficient clearance. Failure to clear such waste leads to formation of toxic protein aggregates implicated in a variety of neurodegenerative diseases, including Alzheimer’s and Parkinson’s. The blood-brain barrier and the glymphatic system are two parallel transport pathways that remove waste from the brain, but very few studies have investigated their interactions or complementary function. Herein, we develop a Lattice Boltzmann simulation of waste clearance from an idealized segment of brain tissue and test the effects of selectively activating or deactivating each pathway. We model clearance of the peptide amyloid-$\beta$, long recognized as critical in Alzheimer’s pathology, and calibrate our model against limited experimental data. This approach uncovers critical parameters that have eluded prior experimental measurement. Our study also reveals complementary functionality of the blood-brain barrier and glymphatic system that are likely generic features applicable to the transport of large molecules (e.g., proteins) in the brain.

A spin $1/2$ is the simplest system that has been believed to support a single two-level quantum system, represented by a single resonance. We experimentally demonstrate that a spin-$1/2$ nucleus of ${}^{19}\mathrm{F}$ in ${\mathrm{C}}_6{\mathrm{F}}_6$ exhibits an extra resonance corresponding to the emergence of the states, by mechanically rotating a sample and a coil in nuclear magnetic resonance (NMR) measurements. On the basis of the Floquet formalism, we identify the emergence of the extra two-level state due to the temporal periodicity generated by the mechanical rotation (mechanical spin multiplexing) and derive an operator algebra analogous to the planar rotor algebra in an effective description of the system. The observed multiplexing allows a single spin $1/2$ to carry more than two states and potentially enabling the processing of multiple quantum bits on a single spin.

We present a new approach to investigating Rydberg molecules by demonstrating the formation and characterization of individual ${\mathrm{Rb}}^{*}\mathrm{Cs}$ Rydberg molecules using optical tweezers. By employing single-atom detection of Rb and Cs, we observe molecule formation via correlated loss of both species and study the formation dynamics with single-particle resolution. We control the interatomic distances by manipulating the relative wave function of atom pairs using the tweezer intensity, optimizing the coupling to molecular states and exploring the effect of the tweezer on these states. Additionally, we demonstrate molecule association with atoms trapped in separate tweezers, paving the way for state-selective assembly of polyatomic molecules. The observed binding energies, molecular alignment, and bond lengths are in good agreement with theory. Our approach is broadly applicable to Rydberg tweezer platforms, expanding the range of available molecular systems and enabling the integration of Rydberg molecules into existing quantum science platforms.

Classical theory asserts that several electromagnetic waves cannot interact with matter if they interfere destructively to zero, whereas quantum mechanics predicts a nontrivial light-matter dynamics even when the average electric field vanishes. Here, we show that in quantum optics, classical interference emerges from collective bright and dark states of light, i.e., particular cases of two-mode binomial states, which are entangled superpositions of multimode photon-number states. This makes it possible to explain wave interference using the particle description of light and the superposition principle for linear systems only. It also sheds new light on an old debate concerning the origin of complementarity.

We introduce a minimal model of a swimmer without body deformation based on force and torque dipoles which allows accurate and efficient 3D Navier-Stokes calculations. Our model can reproduce swimmer propulsion for a large range of Reynolds numbers and generate wake vortices in the inertial regime, reminiscent of the flow generated by the flapping tail of real fish. We perform a numerical exploration of the model from low to high Reynolds numbers and obtain universal laws using scaling arguments. Collecting data from a wide variety of microswimmers, we show that our theoretical scaling laws compare very well with experimental swimming performances across the different hydrodynamic regimes, from Stokes to turbulent flows. The simple design of our generic swimmer model paves the way for efficient large-scale simulations of hundreds of individuals, crucial for understanding collective effects within assemblies of aquatic animals.

We report on time-resolved coherent diffraction imaging of gas-phase silver nanoparticles, strongly heated via their plasmon resonance. The x-ray diffraction images reveal a broad range of phenomena for different excitation strengths, from simple melting over strong cavitation to explosive disintegration. Molecular dynamics simulations fully reproduce this behavior and show that the heating induces rather similar trajectories through the phase diagram in all cases, with the very different outcomes resulting solely from whether and where the stability limit of the metastable superheated liquid is crossed.

We systematically study the acoustocurrent of two-dimensional electron systems in the integer and fractional quantum Hall regimes using surface acoustic waves. We are able to separate the coexisting acoustic scattering and drag, when phonons induce a drag current and tune the electron conductivity, respectively. At large acoustic power, the drag current is finite when the system is compressible and exhibits minima when incompressible quantum Hall states appear. Surprisingly, it exhibits anomalously large bipolar spikes within the quantum Hall plateaus while it vanishes linearly with reduced acoustic power at compressible phases. The current peaks reverse their polarity at the two flanks of exact integer or fractional fillings, consistent with the opposite electric charge of the quasiparticle and quasihole.

Mathematically, topological invariants arise from the parallel transport of eigenstates on the energy bands, which, in physics, correspond to the adiabatic dynamical evolution of transient states. It determines the presence of boundary states, while lacking direct measurements. Here, we develop time-varying programmable coupling circuits between acoustic cavities to mimic the Hamiltonians in the Brillouin zone, with which excitation and adiabatic evolution of bulk states are realized in a unit cell. By extracting the Berry phases of the bulk band, topological invariants, including the Zak phase for the SSH model and the Chern number for the AAH model, are obtained convincingly. The bulk state evolution also provides insight into the topological charges of the newly developed non-Abelian models, which are also verified by observing the adiabatic eigenframe rotation. Our Letter not only provides a general recipe for telling various topological invariants but also sheds light on transient acoustic wave manipulations.

Recent experimental investigations of individual magnetic nanoparticles reveal a diverse range of magnetic relaxation times which cannot be explained by considering their size, shape, and surface anisotropy, suggesting other factors associated with the internal microstructure of the particles are at play. In this Letter, we apply Langer’s theory of thermal activation to fcc Co nanoparticles exhibiting single domain magnetism, whose experimentally observed microstructure contain planar defects. Our analytical derivation yields an expression for the activation rate as a function of the particle size and the defect fraction, enabling a quantitative understanding of the experimental findings. These dependencies, which are exponential for both the Arrhenius exponential and its prefactor, demonstrate the critical role that structural defects can play in the magnetic stability of nanoparticles.

${\mathrm{Na}}_2\mathrm{BaCo}({\mathrm{PO}}_4{)}_2$ is a triangular antiferromagnet that displays highly efficient adiabatic demagnetization cooling [Junsen Xiang et al., Nature (London) 625, 270 (2024)] near a quantum critical point at ${\mu }_0{H}_c\sim 1.6\mathrm{T}$, separating a low-field magnetically disordered from a high-field fully polarized ferromagnetic phase. We apply high resolution backscattering neutron spectroscopy in an applied field to study the magnetic excitations near ${\mu }_0{H}_c$. At large fields we observe ferromagnetic fluctuations that gradually transition to being overdamped in energy below ${\mu }_0{H}_c$ where the magnetism is spatially disordered. We parametrize the excitations in the high-field polarized phase in terms of coupled Zeeman split Kramers doublets originating from the presence of spin-orbit coupling. On reducing the field, the splitting between the Kramers doublets is reduced and if done adiabatically, provides a mechanism for reducing temperature. On lowering the applied field through the ${\mu }_0{H}_c$ the excitations characterize a textured phase that we suggest is inefficient for cooling. Low temperature disordered frustrated magnets built on Kramers doublets with nearby quantum critical points provide a route for efficient magnetocalorics.

Strain engineering enables precise, energy-efficient control of nanoscale magnetism. However, unlike well-studied strain-dislocation interactions in mechanical deformation, the spatial evolution of strain-induced spin rearrangement remains poorly understood. Using in situ Lorentz transmission electron microscopy, we manipulate and observe helical domain reorientation under quantitatively applied uniaxial tensile stress. Our findings reveal striking similarity to plastic deformation in metals, where the critical stress for propagation vector ($\mathit{Q}$) reorientation depends on its angle with the stress direction. Magnetic defects mediate reorientation via “break-and-reconnect” or “dislocation gliding–annihilation” processes. Simulations confirm that strain-induced anisotropic Dzyaloshinskii-Moriya interaction may play a key role. These insights advance strain-driven magnetism and offer a promising route for energy-efficient magnetic nanophase control in next-generation information technology.

We theoretically investigate and experimentally demonstrate that genuine bound states in the continuum (BICs)—polarization-protected BICs—can be completely localized within compact solid resonators. This bound mode is realized in a highly tunable mechanical system made of cylindrical granular crystals, where tuning the contact boundaries enables the in situ transition from the BICs to quasi-BICs in a controllable manner. Since a single-particle resonator can itself support BICs, these bound states can extend to form bound bands within periodic structures composed of such resonators. We experimentally demonstrate the emergence of a quasibound (flat) band in a finite chain with broken resonator symmetry, using a laser Doppler vibrometer. Remarkably, we show that all cylindrical resonators within the entire chain exhibit high-$Q$ and dispersionless resonance.

Recent experimental realizations of liquid-liquid phase separation of active liquid crystals have offered an insight into the interaction between phase separation, ubiquitous in soft matter and biology, and chaotic active flows. In this Letter, we use continuum theory to examine phase separation of an active liquid crystal and a passive fluid and report two new results. First, we provide an analytical derivation of the activity-induced suppression of the phase boundary of the coexistence region—a result first reported in simulations and experiments. We show that the shift in the critical point is a result of the balance between self-stirring active flows and phase-separating diffusive fluxes. Second, we show that this same balance is responsible for dramatically changing the morphology of the phase separated state, resulting in the emergence of a new mixed active phase consisting of a dynamical filamentous active network that invades the entire system area, trapping droplets of passive material. This structure exists even for very low volume fractions of active material. Our work provides an important step towards the goal of understanding how to use activity as a new handle for sculpting interfaces.