We study the Bisognano-Wichmann Hamiltonian for fractional quantum Hall states defined on a sphere and explore its relationship with the entanglement Hamiltonian associated to the state. We present results for several examples, namely, the bosonic Laughlin state stabilized by contact two-body interactions and the bosonic Moore-Read state stabilized by either three- or two-body interactions. Our findings demonstrate that the Bisognano-Wichmann Hamiltonian provides a reliable approximation of the entanglement Hamiltonian as a fully local operator that can be written without any prior knowledge of the specific state under consideration.

The well-known mapping between 1D quasiperiodic systems and 2D integer quantum Hall matter can also be applied in the presence of driving. Here we explore the effect of time-varying electric fields on the transport properties and phase diagram of Harper-Hofstadter materials. We consider light of arbitrary polarization illuminating a 2D electron gas at high magnetic field; this system maps to a 1D quasicrystal subjected to simultaneous phasonic and dipolar driving. We show that this generalized driving generates a tessellated phase diagram featuring a nested duality-protected pattern of metal-insulator transitions. Circularly or elliptically polarized light can create an extended critical phase, opening up a new route to achieving wave function multifractality without fine-tuning to a critical point. We describe in detail a path to experimental realization of these phenomena using lattice-trapped ultracold atoms.

Quasibound states in the continuum (QBICs) in all-dielectric nanostructures provide a promising framework for narrow band perfect absorption due to their high-quality ($Q$) factors and strong field confinement. However, structures supporting isolated bound states in the continuum (BICs) face $Q$-factor limitations due to quadratic scaling with asymmetry parameters. This work introduces a subwavelength silicon grating that supports one symmetry-protected BIC (SP-BIC) at the $\mathrm{\Gamma }$ point and two Friedrich-Wintgen BICs (FW-BICs) at off-$\mathrm{\Gamma }$ points. By tuning the filling factor, these BICs merge topologically, producing a QBIC with enhanced $Q$ factors and stable resonant wavelengths over a broad range of incident angles. When integrated with monolayer graphene, this structure achieves 94.2% absorption at 1311.06 nm with a $Q$ factor of $1.05\times {10}^5$, despite graphenes inherent 2.3% absorption. The high-reflection background reduces radiative losses, surpassing the 50% absorption limit. This study offers a pathway for ultrahigh-$Q$ perfect absorption in dielectric nanostructures, paving the way for advancements in ultrafast optoelectronics.

Symmetry-protected topological (SPT) phases in insulators and superconductors are known for their robust edge modes, linked to bulk invariants through the bulk-boundary correspondence. While this principle traditionally applies to gapped phases, recent advances have extended it to gapless systems, where topological edge-states persist even in the absence of a bulk gap. We extend this framework to periodically driven chains with chiral symmetry, revealing the existence of topological edge zero and $\pi$ modes despite the lack of bulk gaps in the quasienergy spectrum. By examining the half-period decomposition of chiral evolutions, we construct topological invariants that circumvent the need to define the Floquet Hamiltonian, making them more suitable for generalization to the gapless regime. We provide explicit examples, including generalizations of the Kitaev chain and related spin models, where localized $\pi$ modes emerge even when the bulk is gapless at the same quasienergy as the edge modes. We numerically study the effect of interactions, which give a finite lifetime to the edge modes in the thermodynamic limit with the decay rate consistent with Fermi's golden rule.

Non-Hermitian systems can manifest rich static and dynamical properties at their exceptional points (EPs). Here, we identify yet another class of distinct phenomena that is hinged on EPs, namely, the emergence of a series of non-Hermitian conservation laws. We demonstrate these distinct phenomena concretely in the non-Hermitian Heisenberg chain and formulate a general theory for identifying these emergent non-Hermitian conservation laws at EPs. By establishing a one-to-one correspondence between the constants of motion (COMs) at EPs and those in corresponding auxiliary Hermitian systems, we trace their physical origin back to the presence of emergent symmetries in the auxiliary systems. Concrete simulations on quantum circuits show that these emergent conserved dynamics can be readily observed in current digital quantum computing systems.

Chiral superconductivity exhibits the formation of novel electron pairs that breaks the time-reversal symmetry and has been actively studied in various quantum materials in recent years. However, despite its potential to provide definitive information, effects of disorder in the crystal structure on the chiral superconductivity has not yet been clarified, and therefore the investigation using a solid-solution system is desirable. We report muon-spin-relaxation $\left(\mu \mathrm{SR}\right)$ results of layered pnictide ${\mathrm{BaPtAs}}_{1-x}{\mathrm{Sb}}_x$ with a honeycomb network composed of Pt and (As, Sb). We observed an increase of the zero-field muon-spin relaxation rate in the superconducting (SC) state at the Sb end of $x=1.0$, suggesting the occurrence of a spontaneous magnetic field due to the time-reversal symmetry breaking in the SC state. On the other hand, a spontaneous magnetic field was almost and completely suppressed for the As-Sb mixed samples of $x=0.9$ and 0.2, respectively, suggesting that the time-reversal symmetry-breaking SC state in $x=1.0$ is sensitive to disorder. The magnetic penetration depth estimated from transverse-field $\mu \mathrm{SR}$ measurements at $x=1.0$ and 0.2 behaved like weak-coupling $s$-wave superconductivity. These seemingly incompatible zero-field and transverse-field $\mu \mathrm{SR}$ results of ${\mathrm{BaPtAs}}_{1-x}{\mathrm{Sb}}_x$ with $x=1.0$ could be understood in terms of chiral $d$-wave superconductivity with point nodes on the three-dimensional Fermi surface.

We formulate a field-theoretic description for $d$-dimensional interacting nodal semimetals, featuring dispersion that scales with the linear and $n\mathrm{th}$ power of momentum along $d_L$ and $d_M$ mutually orthogonal directions around a few isolated points in the reciprocal space, respectively, with $d_L+d_M=d$, and residing at the brink of isotropic insulation, described by $N_b$-component bosonic order parameter fields. The resulting renormalization group (RG) procedure, tailored to capture the associated quantum critical phenomena, is controlled by a “small” parameter $\varepsilon =2-d_M$ and $1/N_f$, where $N_f$ is the number of identical fermion copies (flavor number) when in conjunction $d_L=1$. When applied to three-dimensional interacting general Weyl semimetals ($d_L=1$ and $d_M=2$), characterized by the Abelian monopole charge $n>1$, living at the shore of the axionic insulation ($N_b=2$), a leading-order RG analysis suggests the Gaussian nature of the underlying quantum phase transition, around which the critical exponents assume mean-field values. A traditional field-theoretic RG analysis yields the same outcomes for simple Weyl semimetals ($n=1, d_L=3$, and $d_M=0$). Consequently, emergent marginal Fermi liquids showcase only logarithmic corrections to physical observables at intermediate scales of measurements.

We study the phases and phase transitions of a disordered one-dimensional quantum $q$-state clock Hamiltonian using large-scale Monte Carlo simulations. Making contact with earlier results, we confirm that the clean, translational invariant version of the model, for $q=6$, hosts an intermediate emergent quasi-long-range ordered (QLRO) phase between the symmetry-broken true long-range ordered (TLRO) phase and the disordered (paramagnetic) phase. With increasing disorder strength, the quasi-long-range ordered phase shrinks and finally vanishes at a multicritical point, beyond which there is a direct transition from the TLRO phase to the paramagnetic phase. After establishing the phase diagram, we characterize the critical behaviors of the various quantum phase transitions in the model. We find that weak disorder is an irrelevant perturbation of the Berezinskii-Kosterlitz-Thouless transitions that separate the QLRO phase from the TLRO and paramagnetic phases. For stronger disorder, some of the critical exponents become disorder-dependent already before the system reaches the multicritical point. We also show that beyond the multicritical point, the direct transition from the TLRO phase to the paramagnetic phase is governed by an infinite-randomness critical point in line with strong-disorder renormalization group predictions. While our numerical results are for $q=6$, we expect the qualitative features of the behavior to hold for all $q>4$.

Quantum measurements profoundly influence system dynamics. They lead to complex nonequilibrium phenomena like the quantum Zeno effect, and they can be used for mitigating errors in quantum simulations. Such an ability is particularly valuable for lattice gauge theories (LGTs), which require the challenging preservation of an extensive number of local conservation laws. While it is known that tailored quantum measurements can soften violations of gauge symmetry, the nature of this protection, and in particular the possibility of a threshold behavior, is still unexplored. Here, we demonstrate the existence of a sharp transition, triggered by the measurement rate, between a protected gauge-theory regime resistant to simulation errors and an irregular regime. Our results are based on the paradigmatic example of a ($1+1$)-dimensional ${\mathbb{Z}}_2$ LGT. We study in detail the protection through projective measurements of ancillary qubits coupled to the local symmetry generators, and compare this approach with analog (weak) measurement protocols. We show that, while the resulting ensemble averages in the continuous-time limit share the same Liouvillian dynamics, different physical implementations of the stochastic gauge protection protocol yield trajectory unravelings with vastly different statistics. Additionally, we design an on-chip feedback mechanism that corrects bit-flip errors and significantly enhances the discrete-time scheme. Our results shed light on the dissipative criticality of strongly interacting, highly constrained quantum systems, and they offer valuable insights into error mitigation and correction of gauge-theory quantum simulations.

We investigate the magnetoelectric properties of the monolayer ${\mathrm{Ni}X}_2$ ($X$ = Br, I) through first-principles calculations. Our calculations predict that the ${\mathrm{NiBr}}_2$ monolayer exhibits a cycloidal magnetic ground state. For the ${\mathrm{NiI}}_2$ monolayer, a proper-screw helical magnetic ground state with modulation vector $\mathit{Q}=(q,0,0)$ is adopted and approximated based on experimental observations. The electric polarization in ${\mathrm{NiBr}}_2$ shows a linear dependence on the spin-orbit coupling strength ${\lambda }_{\text{SOC}}$, which can be adequately described by the generalized Katsura-Nagaosa-Balatsky (gKNB) model, considering contributions from up to the third-nearest-neighbor spin pairs. In contrast, the electric polarization in ${\mathrm{NiI}}_2$ exhibits a distinct dependence on $q$ and ${\lambda }_{\text{SOC}}$, which cannot be fully explained by the gKNB mechanism alone. To account for this, we incorporate the higher-order $p\text{−}d$ hybridization mechanism, demonstrating that the magnetoelectric behavior in ${\mathrm{NiI}}_2$ arises from the combined effects of the gKNB model and $p\text{−}d$ hybridization. Furthermore, we quantitatively extract their respective contributions, providing a comprehensive understanding of magnetoelectric coupling in monolayer ${\mathrm{NiBr}}_2$ and ${\mathrm{NiI}}_2$, with implications readily applicable to their bulk counterparts.

Topological spin superconductors are $p$-wave spin-triplet exciton insulators whose topological edge modes have been shown to obey non-Abelian braiding statistics. Based on a toy model as the spin counterpart of the Kitaev's chain, we study the spin Josephson effect adopting the $S$ matrix as well as the Green's function method. The on-site energies of these topological edge modes lead to a transition between the fractional and integer spin Josephson effects. Moreover, nonvanishing on-site energies will also induce a charge pump through the spin Josephson junction. These two effects, distinct features of topological spin superconductors and absent in Majorana systems, can be utilized for spin transport detection of topological spin superconductors.

One-dimensional superconductor-semiconductor nanowires are leading candidates for topological quantum computation because of their ability to host non-Abelian Majorana zero modes (MZMs). However, standard methods for identifying MZMs are often inadequate, particularly in the presence of disorder, where many properties considered to be heralds of MZMs are often generated by trivial disorder-induced Andreev bound states. Recent studies clearly indicate the need for developing new techniques for identifying and diagnosing MZMs. In this study, we use a generalized vision transformer-based neural network to predict, using tunnel conductance measurements, whether a device manifests a topological MZM phase in the presence of disorder and to map out the entire topological phase diagram. We demonstrate the ability of our method to classify with arbitrary confidence $(P>0.9998)$ whether a device as possesses a a nontrivial MZM-carrying topological phase for a wide variety of disorder parameters. We also show an ability to predict from conductance measurements alternative (to the extensively used scattering-matrix-invariant topological indicator) Majorana indicators based on local density of states (LDOS). This is relevant because topology may not be uniquely defined by the scattering invariant in short disordered wires. This work serves as a significant advance, offering a step toward the practical realization of Majorana-based quantum devices, allowing a deep-learning understanding of the topological properties in disordered nanowire systems. We validate our method using extensive simulated Majorana results in the presence of disorder and suggest employing this technique for the analysis of experimental data in superconductor-semiconductor hybrid Majorana platforms.

A mechanism of nonreciprocal transmission of sound through a viscous environment with asymmetric scatterers is proposed and experimentally demonstrated using a Tesla valve filled by stationary liquids with different viscosities. The nonreciprocal quantity is the local intensity of sound. Unlike pressure, which remains reciprocal even in a viscous fluid, the intensity exhibits nonreciprocity due to the asymmetry of the field of acoustic velocities if the mirror symmetry ($P$ symmetry) is broken by asymmetric scatterers. Nonreciprocity in intensity appears in the linear regime of propagation, while the intensity itself scales quadratically with the amplitude of sound. Our study supports the general conclusion that Newton's dynamics of a system with broken time-reversal symmetry ($T$ symmetry) is nonreciprocal. Due to the irreversibility of viscous fluid dynamics, the dissipation-induced nonreciprocity does not follow Onsager symmetry, unlike nonreciprocity caused by fluid motion or magnetic field.

The band structure of spin waves in chiral magnonic superlattices is theoretically studied. The proposed metamaterials involve a thin ferromagnetic layer in contact with a one-dimensional array of heavy-metal stripes, causing a periodic interfacial Dzyaloshinskii-Moriya interaction. Two superlattice configurations are examined in this research, with attention given to either heavy-metal stripe extraction from the supercell, which contains several stripes, or modification of the central stripe width. For the first class, dispersionless modes are found within the band gaps associated with the regular chiral magnonic crystal. A fine structure is also obtained for the low-frequency flat bands, where a set of subbands shows the typical quantization of laterally confined waves. In the second class of superlattices, defect modes are observed, which have properties similar to those seen in nonchiral magnonic crystals with defects. Nonetheless, additional low-frequency flat modes with a notable localization in the defect region are predicted, which emerge at a frequency even lower than the lowest band of the defect-free chiral magnonic crystal. Micromagnetic simulations agree with the predicted behavior from the plane-wave method calculations, reinforcing the theoretical modeling of the chiral superlattices. These results are relevant for developing magnon-based devices relying on nonreciprocity and channeling of the spin waves.

We present protocols for preparing two-dimensional Abelian and non-Abelian topologically ordered states by employing finite depth unitary circuits composed of long-ranged, simultaneous, and mutually commuting two-qubit gates. Our protocols are motivated by recent proposals for circuits in trapped ion systems, which allow each qubit to participate in multiple gates simultaneously. Our circuits are shown to be optimal, in the sense that the number of two-qubit gates and ancilla qubits scales as $O\left(L^2\right)$, where $L$ is the linear size of the system. Examples include the ground states of the toric code, certain Kitaev quantum-double models, and string-net models. Going beyond two dimensions, we extend our scheme to more general Calderbank-Shor-Steane codes. As an application, we present protocols for realizing the three-dimensional Haah's code and X-cube fracton models.

Sliding ferroelectricity is induced by the artificial stacking of two-dimensional materials, and with specific stacking sequences, it can even emerge in nonferroelectric layered systems. Here, based on first-principles calculations, we demonstrate that multilayer black phosphorus (BP) with layer number $N\ge$ 3 exhibits ferroelectricity. The polarization originates from symmetry breaking induced by layer stacking and can be reversed through the relative sliding of adjacent layers. With an increasing number of layers, a greater diversity of polarization states emerges, highlighting the crucial role of layer number and interlayer dipole coupling in sliding ferroelectricity. Surface-layer displacement in BP slabs also generates spontaneous polarization, offering opportunities for experimental detection and manipulation. Our work establishes interlayer sliding as an effective approach to induce ferroelectricity in elemental multilayers, opening new possibilities for nonvolatile memory applications.