Optical beams with orbital angular momentum (OAM) have numerous potential applications, but the means used for their generation often lack crucial on-demand control. In this work, we present a mechanism of converting spin angular momentum (SAM) to OAM in a nonstructured beam. The conversion occurs through spin-orbit coupling in a reconfigurable photonic honeycomb lattice with staggering implemented by electromagnetically induced transparency in an atomic vapor cell. The spin-orbit coupling allows to outcouple the OAM signal from a particular band in a given valley determined by the chirality of light or the lattice staggering, providing a nonzero Berry curvature for generating OAM. The dependence of the output OAM on the chirality of the input beam is the first control knob. The staggering works as a second control knob, flipping the sign of OAM for the fixed chirality. The demonstrated conversion between SAM and OAM is important for optical communications. Our results can be extended to other implementations of paraxial photonic graphene.

A broad class of correlated quantum materials features strong Hund’s coupling, yet cold-atom quantum simulators have so far focused primarily on single-orbital Fermi-Hubbard systems near a Mott insulator. Here, we show that repulsively interacting fermions loaded into the $p$ bands of a hexagonal lattice offer a unique platform to study the interplay of “Hundness” and “Mottness.” Our theory predicts that the orbital degrees of freedom, despite geometric frustration, produce a rich phase diagram featuring a competing itinerant ferromagnetic (FM) metal and a spin-1 antiferromagnetic (AFM) insulator. While FM order is known to emerge at low fillings near the flat-band limit, we show that this itinerant ferromagnetism is remarkably robust, persisting to stronger interactions and higher fillings well beyond the flat-band regime. More importantly, we identify that near half filling, FM is stabilized by a different mechanism: the double exchange with spins aligning to avoid Hund-rule penalties at the expense of the kinetic energy of Dirac fermions. The competition between the kinetic and double-exchange energies leads to, within our approximations, a first-order transition between FM and AFM orders in the chemical potential-interaction strength plane. Our analysis suggests that $p$-orbital Fermi gases—as multiorbital systems with coexisting localized and itinerant spins—reveal a rich competition between correlated “Hund metals” and other unconventional states driven by quantum fluctuations.

We investigate the interplay between charge, magnetic, and structural degrees of freedom in the isostructural and isoelectronic $5d^1$ double perovskites ${\mathrm{Ba}}_2{\mathrm{MgReO}}_6$ and ${\mathrm{Ba}}_2{\mathrm{NaOsO}}_6$. Using first-principles-based electronic structure calculations, we show that both materials exhibit a tendency toward spontaneous quadrupolar order in the cubic paramagnetic phase, which is slightly weaker in ${\mathrm{Ba}}_2{\mathrm{NaOsO}}_6$ than in ${\mathrm{Ba}}_2{\mathrm{MgReO}}_6$. Our analysis further reveals an intimate coupling between the local magnetic moments and charge quadrupoles, mediated by the strong spin-orbit interaction, that leads to the unusual canted configuration of magnetic moments observed in these systems. When structural degrees of freedom are included, the two materials exhibit pronounced differences. In ${\mathrm{Ba}}_2{\mathrm{MgReO}}_6$, the strong coupling to Jahn-Teller distortions stabilizes the antiferroic ${\mathcal{Q}}_{x^2-y^2}$ order, yielding excellent agreement with available experimental data. In contrast, the Jahn-Teller coupling is significantly weaker in ${\mathrm{Ba}}_2{\mathrm{NaOsO}}_6$ and appears insufficient to stabilize the antiferroic quadrupolar order. While this is consistent with the absence of any measurable long-range structural distortion above the magnetic transition temperature, it contrasts with experimental results indicating a strong canting of the magnetic moments. Our analysis thus successfully describes the mechanisms shaping the properties of the Re compound while a full quantitative description of the magnetic ground state of ${\mathrm{Ba}}_2{\mathrm{NaOsO}}_6$ is still elusive.

Thermal counterflow of superfluid ${}^4\mathrm{He}$ past a cylinder produces quasisteady eddies not only downstream but also anomalously upstream. However, the mechanism and organizing principles behind the observed multistable wake topologies (zero-, two-, four-, and six-vortex states) have remained unclear. We show that the full spectrum of reported normal-fluid wake states is captured numerically with a two-fluid model coupled to Vinen’s vortex-line-density equation. Our simulations further reveal that the superfluid component can also develop anomalous upstream eddies, a feature not previously reported. We trace these behaviors to a self-organized zone of enhanced mutual-friction dissipation near the cylinder shoulders that reshapes the effective obstacle, drives upstream eddies in both components, and suppresses intrinsic wake oscillations in the normal fluid. Guided by this mechanism, we perform systematic parameter scans and construct a unified phase diagram in terms of the normal-fluid Reynolds number ${\text{Re}}_n$ and a dimensionless interaction number $N$, separating inertia- and mutual-friction-controlled transitions and delineating the parameter windows for the discrete wake topologies. These results turn a striking phenomenology into a predictive map and establish mutual-friction feedback as a robust route to unusual wake structures in quantum fluids.

We address the problem of how to prepare single-spinon wave functions, relevant for one-dimensional $S=1/2$ spin models, in a quantum computer. We adopt the recently proposed ansatz [Kulka et al., Phys. Rev. Lett. 134, 236504 (2025)] for the single-spinon wave function, where a state with $S=1/2$ is built in a spin chain with $L+1$ sites, adding a site with $S_z=1/2$ to the configurations of the ground-state wave function for the spin chain with length $L$. We extend the original work to the case of the Haldane-Shastry model. We discuss how to prepare the single-spinon ansatz for both the Heisenberg and Haldane-Shastry models in quantum computers, using a linear combination of unitaries. We consider three different strategies to compute the single-spinon energy in a quantum computer, we analyze their cost in terms of the number of qubits, gates, and circuits, and we test them in silico.

The observation of pressure-induced superconductivity in two- and three-layer Ruddlesden-Popper nickelates has spurred intense interest in these materials as a platform for exploring unconventional superconductivity. While the ground state of these systems has been shown to exhibit magnetism, the direct determination of their magnetic structure remains elusive. This is a crucial aspect, as magnetism may play a role in the pairing mechanism of superconductivity in these materials. In this study, we resolve the magnetic structures in the bilayer (2222) polymorphs of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ and ${\mathrm{La}}_2{\mathrm{PrNi}}_2{\mathrm{O}}_7$ compounds, using a combination of complementary techniques, namely, neutron powder diffraction and muon-spin rotation/relaxation ($\mu \mathrm{SR}$). Magnetic neutron scattering in both samples emerges below $\sim 150$ K and is observed at the ($q_x,\frac{1}{2},0$) position, with $q_x=0$ and $\frac{1}{2}$ for ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ and $q_x=0$ for ${\mathrm{La}}_2{\mathrm{PrNi}}_2{\mathrm{O}}_7$. Alternating low-magnetic-moment (0.05–$0.075{\mu }_{\text{B}}$) and high-magnetic-moment ($0.66{\mu }_{\text{B}}$) stripes form a single layer; the bilayers are formed through antiferromagnetic stacking of single layers along the out-of-plane direction. The magnetic scattering with two propagation vectors $q_x=0$ and $\frac{1}{2}$ in the undoped ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ is attributed to two magnetic stacking polymorphs within a single crystallographic phase. The magnetic structures are substantiated by the $\mu \mathrm{SR}$ spectra. These findings provide a detailed understanding of the magnetic ground state in bilayer nickelates, offering crucial insights into the possible precursor states that may influence the emergence of superconductivity in these materials.

Hyperspectral photoluminescence maps of moiré transition-metal dichalcogenide heterobilayers encode rich information about the underlying disorder, but extracting it is hampered by the ambiguity of assigning individual spectral peaks. We show that the spatial correlations among a set of simple, peak-decomposition-free spectral descriptors—such as the centroid energy, the dominant-peak energy, and a sharp-line fraction—provide a peak-decomposition-free route to infer features of that disorder. Different descriptors act as filters that select different components of a multiscale disorder landscape—a smooth, micron-correlated background and a dense set of localized traps—and therefore acquire different spatial correlation lengths. The central prediction is a correlation-length hierarchy, $\xi \left(E_{\mathrm{cent}}\right)\ge \xi \left(E_{\mathrm{dom}}\right)$, which we derive by splitting the dominant-peak energy into a smooth background part and a short-range trap-switching fluctuation. The same picture explains the measured interdescriptor correlations, including the near-perfect anticorrelation ${\rho }_{\mathrm{S}}(\mathrm{\Delta }{E}_{\mathrm{cd}},R_{\mathrm{HL}})\approx -0.978$, which we show to be a robust geometric trend for spectra dominated by a common emission-envelope asymmetry. Benchmarked against phenomenological simulations, Hamiltonian diagonalization, and the measured ${\mathrm{MoSe}}_2/{\mathrm{WSe}}_2$ descriptor correlations, the framework turns descriptor maps into a quantitative, peak-decomposition-free probe of slow disorder and local traps in moiré excitons and, more broadly, in disordered semiconductor emitters.

Nonlinear integrated optical devices that can realize threshold filtration of signals are in demand in photonics and optical computing. However, a list of requirements exists for such devices to make them practical. Here, to design a thresholder with the desired behavior, we suggest a mechanism that implements the property of resonators to provide extremely sharp (with respect to the wavelength) $\pi$ phase shifts near the critical coupling regime. By combining this feature with a nonlinear switching mechanism, one may obtain highly sensitive devices. Notably, the sharpness of the phase step in the considered case is independent of the quality factor of the resonators and the corresponding width of the resonances in transmittance. Instead, it is defined by the proximity to the critical coupling regime. Balancing near the critical coupling allows one to vary the sensitivity and achieve controllable smearing of the step function. The described effect is quite robust and can be realized for different materials and types of nonlinearity. The possibility of using sharp steps and low-quality resonators simultaneously provides multiple advantages for the resulting device. These include compact size, low manufacturing requirements, high operation speed, and low switching intensities. These sensitive and tunable phase thresholders may have multiple applications in optical computing. Few examples are provided, including a minimally invasive logic gate and a signal intensity classifier. In particular, the considered thresholders are useful in neuromorphic chips since they may act as optical neurons. In this paper, we provide an example of a photonic scheme that represents the behavior of a neuron and discuss its characteristics. Both the amplitude and phase of light are actively used in the scheme to store and update the state of a neuron.

The Kitaev model is an exactly solvable model that exhibits a quantum spin liquid as its ground state. While this model was originally proposed as an $S=1/2$ spin model on a honeycomb lattice, extensions to higher-spin systems have recently attracted attention. In contrast to the $S=1/2$ case, such higher-$S$ models are not exactly solvable and remain poorly understood, particularly for spin excitations at finite temperatures. Here, we focus on the $S=1$ Kitaev model, which has been proposed to host bosonic quasiparticles. We investigate this model using Schwinger boson mean-field theory, where bosonic spinons are introduced as fractional quasiparticles by extending bond operators to address anisotropic spin interactions. We determine the mean-field parameters that realize a quantum spin liquid in both ferromagnetic and antiferromagnetic Kitaev models. Based on this mean-field ansatz, we calculate the dynamical and equal-time spin structure factors. We find that, when one uses the conventional decoupling scheme based on Wick decoupling with respect to spinons to calculate spin correlations, the resultant spin structure factors exhibit a momentum dependence that is not consistent with the sign structure expected from the exchange interaction: They possess a strong spectral weight indicating ferromagnetic (antiferromagnetic) correlations in the antiferromagnetic (ferromagnetic) Kitaev model. To resolve this issue, we propose an alternative scheme for evaluating the spin correlations, which is based on decoupling with respect to the bond operators. We demonstrate that, in our scheme, this discrepancy is removed, and the momentum dependence of the spin structure factors is consistent with the sign of the exchange constant. We also calculate the temperature evolution of the dynamical spin structure factor and find that the continuum observed at zero temperature splits into two distinct structures as the temperature increases, which can be understood in terms of the bandwidth narrowing of spinons. Finally, we clarify the origin of why the two distinct decoupling schemes result in different momentum dependences of the spin structure factors and discuss their relationship to results obtained in previous studies.

The Green’s function theory of Lymar’ and Rudoi [Theor. Math. Phys. 21, 990 (1974)] is generalized to the case of multiple intra- and intersublattice magnetic interactions in a collinear spin-half antiferromagnet and applied to magnetic excitations in ${\mathrm{Bi}}_2{\mathrm{CuO}}_4$. The spin Hamiltonian includes both the out-of-plane and in-plane symmetric anisotropy terms and the Zeeman term, which describes the interaction with an external magnetic field $B$ applied along the Néel vector. Within the spin-wave approximation, we calculate spin excitation dispersion, antiferromagnetic resonance frequencies, and the critical field $B_c$ of the spin-flop metamagnetic transition. A weak in-plane anisotropy is shown to result in a gap in the acousticlike branch of the excitations. The gap nonlinearly depends on the external field and closes at $B=B_c$. An expression for the Néel temperature in the Tyablikov random phase approximation at zero field is derived. For the parameters derived from the recent inelastic neutron scattering study by Yuan et al. [Phys. Rev. B 103, 134436 (2021)], it gives $T_{\mathrm{N}}\approx 52\mathrm{K}$.

Roughness-insensitive surface magnetization is an intrinsic property of magnetoelectric antiferromagnets and is today understood as a manifestation of bulk magnetoelectric multipoles. Here, we provide an experimental quantification of the crystal-facet-dependent surface magnetization in the archetypical magnetoelectric antiferromagnet ${\mathrm{Cr}}_2{\mathrm{O}}_3$ and show that the data are consistent with a quadrupolar component of the bulk magnetoelectric multipolization. Using quantitative nanoscale magnetometry on lithographically defined rectangular mesas that expose 30 distinct crystallographic facets, we quantify mesa stray magnetic fields, which arise from differences between the mesa top and side-facet magnetizations. The resulting dataset supports a linear map from surface normal to surface magnetization, from which we directly infer the bulk quadrupolar component within the multipolization framework. Our work provides systematic, facet-resolved evidence of roughness-insensitive surface magnetization, including in-plane components, and delivers a quantitative route to constraining bulk multipoles from surface stray-field data. Beyond addressing the modern theory of magnetoelectric multipolization, our approach offers a generally applicable method to quantify surface magnetizations in antiferromagnetic compounds and informs the choice of crystal cuts for future spintronics devices.

Non-Hermitian topological matter provides a platform for engineering phenomena that go beyond the capabilities of Hermitian systems, enabling the use of losses to engineer topological phenomena. Non-Hermitian models often rely on artificial platforms made of engineered lattices because controlling losses in natural compounds is challenging. Although typical models for non-Hermitian photonic matter are often single mode, photonic systems are often multimodal, producing mixing between different normal modes in each site. Here, we explore a family of multimodal non-Hermitian lattices, featuring multiple resonant modes. We show that these multimodal models are capable of featuring topological modes and criticality, similar to the artificial single-mode models often considered. We analyze the robustness of these non-Hermitian topological modes to fluctuation of local losses, disorder, and artificial gauge field. We show that these effects can be captured via both a full microscopic model and effective multiorbital models. Specifically, we show that due to their multiorbital nature, the localization properties of non-Hermitian multiorbital models can be controlled by an external gauge field. Our results demonstrate that internal orbital degrees of freedom provide a promising strategy to engineer controllable non-Hermitian topology and criticality.

Nonlinear response functions, formulated as multipoint correlation functions or Volterra kernels, encode the dynamical and spectroscopic properties of physical systems and underpin a wide range of nonlinear transport and optical phenomena. However, their evaluation rapidly becomes prohibitive at high orders because of combinatorial (often factorial) scaling or severe numerical errors. Here, we establish a systematic and efficient framework to compute nonlinear response functions directly from real-time dynamics, without explicitly constructing multipoint correlators or relying on numerically unstable finite-difference methods for order-resolved extraction. Our approach is based on the Gateaux derivative with respect to the external field in function space, which yields a closed hierarchy of tangent equations of motion (TEOM). Propagating the TEOM alongside the original dynamics isolates each perturbative order with high accuracy, providing a term-by-term decomposition of physical contributions. The computational cost scales exponentially with response order in the fully general setting and reduces to polynomial complexity when all perturbation directions are identical; both regimes avoid the factorial scaling of explicit multipoint-correlator evaluations. We demonstrate the power of TEOM by computing frequency-resolved fifth-order response functions for a solid-state electron model and by obtaining nonlinear response functions up to the 49th order with controlled accuracy in a classical Duffing oscillator. We further show that our time-evolution formulation allows optical conductivities to be evaluated directly while remaining numerically stable even near zero frequency. TEOM can be incorporated seamlessly into existing real-time evolution methods, yielding a general framework for computing nonlinear response functions in quantum and classical dynamical systems.

Quantum many-body scarring (QMBS) has emerged as an intriguing paradigm of weak ergodicity breaking in nonintegrable quantum many-body models, particularly lattice gauge theories (LGTs) in $1+1$ spacetime dimensions. However, an open question is whether QMBS has a true high-energy physics origin, and thus exists in higher-dimensional LGTs with dynamical matter. Given that nonergodic dynamics in $d=1$ spatial dimension tend to vanish in $d>1$, it is important to probe this question. Using matrix product state techniques for both finite and infinite systems, we show that QMBS occurs in the $2+1\mathrm{D} \mathrm{U}\left(1\right)$ quantum link model, as evidenced in persistent coherent oscillations in local observables, a marked slowdown in the growth of the bipartite entanglement entropy, and revivals in the fidelity. Interestingly, we see that QMBS is more robust when the matter degrees of freedom are bosonic rather than fermionic, which we argue is due to the strong nonlocality of the wave function in the latter case. Our results further shed light on the intimate connection between gauge symmetry and QMBS, and highlight the persistence of scarring in higher spatial dimensions. Our findings can be tested in near-term analog and digital quantum simulators, and we demonstrate their accessibility on a recently proposed cold-atom analog quantum simulator.

The interplay between disorder and topology has become a central theme in condensed matter physics. Disorder can not only destroy topological phases but also induce them, as exemplified by the topological Anderson insulator (TAI). Here, we show that, in close analogy, disorder can drive the clean-limit, time-reversal-broken (T-broken) quantum spin Hall state of ferromagnetic monolayer ${\mathrm{MnBi}}_4{\mathrm{Te}}_7$ into a quantum anomalous Hall phase, which was called topological Anderson Chern insulator (TACI). Using density functional theory and nonequilibrium Green's function calculations in the presence of disorder, we identify disorder-induced phases, including T-broken TAI, TACI, normal insulator, etc., and then construct a comprehensive phase diagram. To discriminate multiple phases in the strong-disorder regime, we further use the density of states computed within the self-consistent Born approximation, which, in particular, distinguishes gapped and ungapped topological phases. We find that the two effective band inversions of Hamiltonian are suppressed at distinct critical disorder strengths; the survival of a single inversion over a finite disorder window stabilizes the TACI. The region of quantized Hall resistance is not confined to the band gap but extends into a mobility gap, substantially enlarging the parameter space exhibiting quantization. Remarkably, at strong disorder, we further propose a zero Hall plateau insulating state characterized by an insulating bulk and edge channels subject to diffusive scattering that can coexist with the TACI. This behavior is distinct from a conventional band-gap Chern insulator and provides a clear experimental signature. Compared with the clean region, the expansion of the energy window supporting the Chern insulator of the disordered region enhances thermal robustness and enables observation of the quantum anomalous Hall effect at higher, technologically relevant temperatures, advancing both fundamental studies and potential applications.

Type-II semi-Dirac fermions in two dimensions have been proposed to describe topologically nontrivial low-energy excitations in titanium/vanadium oxide heterostructures. These quasiparticles appear at the merger of three Dirac cones, resulting in a nonzero Berry phase. We find, by employing Hartree-Fock, renormalization group, and random phase approximation techniques, that the spectrum is very sensitive to long-range electron-electron interactions and can undergo a profound transformation. Our results indicate that at the topological phase boundary, long-range correlations stabilize a hybrid electronic phase displaying both Dirac and type-II semi-Dirac qualities, with physical characteristics exhibiting continuously varying critical exponents as a function of the Fermi energy; for example, Landau levels in a magnetic field vary with the energy scale: $|{\varepsilon }_n{\left(B\right)|\sim \left(nB\right)}^{1/2}\to {\left(nB\right)}^{3/4},n\in {\mathbb{N}}_0$. The quasiparticle spectrum evolves, driven by interactions, from anisotropic Dirac dispersion at the lowest energies toward the characteristic type-II semi-Dirac boomerang shape as the energy increases. The corresponding density of states concomitantly varies between linear and power one-third ($\rho \left(\varepsilon \right)\sim \left|\varepsilon \right|\to {\left|\varepsilon \right|}^{1/3}$). The crossover scale is controlled by the interaction strength $\alpha =e^2/\left(\hslash v\right)$ and the specifics of the effective interacting Hamiltonian.

We develop a unified field-theoretical description of the Bose-Hubbard model that captures low-energy dynamics across the insulator-to-superfluid transition. We show that commonly used cumulant expansions about the Mott ground state fail in the superfluid phase not only quantitatively but also fundamentally, because they impose an incorrect canonical structure. Expanding instead about the appropriate mean-field saddle point, we derive an effective action in which the dynamics of fluctuations are governed by a Berry-phase term, giving rise to an emergent magnetic field in the associated oscillator description. This field encodes particle-hole symmetry breaking in both the Mott-insulator phase and the superfluid, and vanishes at the point where a pure Goldstone mode emerges. The resulting effective hydrodynamic theory admits a speed of sound that approaches the Bogoliubov limit in the weakly interacting regime, demonstrating consistency across the entire phase diagram, from the Mott-insulator to the deep superfluid regime. While the total density remains continuous within mean-field theory, we find that quantum fluctuations generate a discontinuous contribution at the quantum phase transition, which vanishes at the tip of the Mott lobe.

We study the equilibrium and nonequilibrium formation of four-particle complexes in a balanced two-species Bose-Hubbard model with repulsive intraspecies and attractive interspecies interactions. Using exact diagonalization, we characterize the transition from weakly to strongly correlated dimer and tetramer states along the one- to two-dimensional crossover in coupled-chain geometries by combining local correlation signatures with global diagnostics such as the binding energy and interspecies entanglement entropy. We show that transverse connectivity between chains qualitatively reshapes the phase diagram, substantially enlarging the tetramer region and, in particular, stabilizing weakly bound tetramers when compared to the one-dimensional chains. By tuning the interchain hopping, we identify a transition from a degenerate manifold of spatially separated dimers to a localized tetramer ground state, driven by the lifting of one-dimensional configurational degeneracies and an associated kinetic-energy gain. By extending our analysis to larger complexes of six and eight particles, we reveal that these binding mechanisms are robust and suggest a general pathway for the formation of higher-order complexes. Finally, we demonstrate interaction and geometric quench protocols to dynamically prepare these complexes with high fidelity. Our results provide a microscopic framework for engineering and probing few-body bosonic bound states in tunable lattice geometries.

We investigate the spectral and topological properties of an atomic chain of red phosphorus. We reveal the separation of flat-band states from the rest of the system and calculate its energy bands analytically. The topological properties of the system are established through the evaluation of the Berry (Zak) phase of the energy bands, revealing nontrivial topology. The Berry phase depends on the relative strength of the hopping parameters and exhibits dual energy-dependent topological phase transitions. Remarkably, the emergence of inert band edges provides a direct spectral signature of these transitions, acting as energy-resolved indicators of the redistribution of topological charge between bands. The existence of the associated edge states is proved numerically for finite lattices. The theoretical predictions, particularly the band structure and the existence of edge states, are further confirmed by numerical simulations of red phosphorus through a phononic lattice in the form of a highly structured aluminum plate.