arXiv subjects

Wu-Ming Liu

Publications and source records attributed to Wu-Ming Liu.

At least 19 recordsLinked to original sources

arXiv2026

Quantum-geometry stabilization of dilute fractional Chern insulators

Fractional Chern insulators have attracted broad interest as lattice analogs of fractional quantum Hall states without Landau levels. However, low-filling fractional Chern insulators are fragile because charge-ordered phases can compete strongly with the fractional topological liquid. Here, we propose a center-decorated kagome model, motivated by geometry-tunable artificial lattices, in which the center-site hopping $t_2$ provides a direct knob for the quantum geometry of an isolated $C=1$ flat band. Here quantum geometry refers to the Berry curvature and Fubini--Study metric, which determine the form factors of interactions projected into the Chern band. Exact diagonalization shows that tuning $t_2$ away from the flatness-optimized kagome limit reduces the trace-condition deviation, suppresses competing charge order, and enhances the many-body stability at both $\nu=1/3$ and the more fragile $\nu=1/5$ filling. At $\nu=1/5$, this stability-enhanced window persists under nearby interaction profiles, including variations of the dominant third-neighbor repulsion and weak nearest-neighbor admixtures. Low-energy spectra, spectral flow, quasihole and entanglement counting, static structure factors, and the quantized total many-body Chern number $C_{\mathrm{tot}}=1$ consistently support Laughlin-like fractional Chern insulators. These results identify quantum-geometry engineering as a route to stabilizing dilute fractional Chern insulators beyond band-flatness optimization alone.

cond-mat.str-el↗

arXiv2026

One-dimensional Polar Spinor Droplets

We derive a channel-resolved Lee-Huang-Yang correction and construct an extended GrossPitaevskii model for one-dimensional polar spin-1 quantum droplets. The fluctuation contribution separates into density and spin channels, which supports self-bound droplets even when the spinindependent mean-field interaction is repulsive. Stationary solutions exhibit a continuous crossover from soliton-like to flat-top droplets, accompanied by saturation of the chemical potential and peak density as the particle number increases. Within the parameter range examined here, linear Bogoliubov analysis together with weak-perturbation dynamics supports the stability of both droplet types. A quadratic-Zeeman quench reveals a finite-size crossover in breathing dynamics and distinct nonequilibrium roles of the density and spin fluctuation channels. Representative head-on collisions further show that the finite-size crossover modulates phase-sensitive nonlinear scattering, with in-phase impact producing coalescence-like central retention and out-of-phase impact favoring quasi-elastic separation. The analysis clarifies how density and spin fluctuations shape equilibrium structure and nonequilibrium response in low-dimensional polar spinor droplets.

cond-mat.quant-gas↗

arXiv2026

Ripple Signatures of Majorana Hybridization across a Topological Quantum Quench

The crossover between topology and nonequilibrium dynamics has emerged as a rich frontier, in which quantum systems can exhibit unique dynamical phenomena that lie beyond the reach of equilibrium. Of particular interest are quench dynamics across topological phase, as it may reveal the information about the underlying Majorana zero-energy states. Here, we investigate the fate of Majorana boundary modes in a quenched fermionic superfluid using self-consistent time-dependent Bogoliubov-de Gennes theory. For quantum quenches within the topological regime, Majorana boundary modes survive but undergo coherent boundary oscillations arising from the nonadiabatic deformation of their wave functions. Furthermore, a pronounced ripple pattern appears in the post-quench density distribution following a sudden topology-changing quench. Here we identify that these ripple structures originates from the coherent hybridization and interference of the initially separated Majorana boundary states. Our findings establish nonequilibrium boundary dynamics as a new approach for probing Majorana physics, which is complementary to conventional equilibrium measurements.

cond-mat.quant-gas↗

arXiv2026

Memory and thermal amplification in spin--cavity squared commutators

Squared commutators in the Holstein--Primakoff limit of a spin--cavity system provide a compact way to separate propagation from covariance growth in a finite-temperature reservoir with memory. In the finite-temperature NMQSD construction, the linear quadrature commutator is fixed by the retarded spin--cavity propagator, whereas a quadratic commutator carries the same retarded factor together with a covariance factor. For a zero-mean Gaussian state, $C_{R_i^2,R_j}(t)=4|\kappa_{ij}(t)|^2V_{ii}(t)$; the symmetrized expression gives the spin-side and mixed channels. Since $\bar n$ enters the covariance sector but not the homogeneous retarded kernel, raising $\bar n$ from 0 to 1 leaves the linear transfer unchanged while increasing the quadratic signal. Varying the bath-memory rate and the counter-rotating coupling within the stable HP region then shows how stored cavity history changes both the transfer weight and its distribution in time. The calculation separates memory-dependent propagation from thermal covariance growth in collective spin--cavity dynamics.

quant-ph↗

arXiv2026

Shear Viscosity at the van Hove singularity

The applicability of the semiclassical Boltzmann transport theory is fundamentally challenged in strongly correlated systems where quasiparticle excitations are ill-defined. When the fermion spectral broadening becomes much larger than the boson broadening, the Boltzmann approach to transport is not always valid, particularly in the dirty limit of the critical regime. Using a diagrammatic Kubo formalism, we compute several critical transport coefficients at a van Hove singularity and show that, while the conductivity happens to agree with the Boltzmann result, the dc shear viscosity exhibits qualitatively different behavior. The diagrammatic Kubo results are more reliable because, under the fermion sharp peak approximation--an assumption that strictly breaks down in the dirty critical limit--we demonstrate that the leading order Feynman diagrams reduce to the Boltzmann equation. The same critical model, which can also account for strange metal, makes experimentally testable predictions for the optical and dc shear viscosities, ${\rm Re}[\eta(\Omega)]\sim (|\Omega|^{3/2}+T^{3/2})/\Omega^2$ and ${\rm Re}[\eta(\Omega=0)]\sim T$, providing further opportunities to assess the validity of our theoretical framework.

cond-mat.str-el↗

arXiv2026

Fractional Chern insulator with higher Chern number in optical lattice

Fractional Chern insulators arise in topologically nontrivial flat bands, characterized by an integer Chern number C that corresponds to the number of dissipationless edge states in the non-interacting regime. Higher Chern numbers can replicate the physics of higher Landau levels and often confer enhanced topological robustness. However, realizing correlated fractional phases with higher Chern numbers in such flat band systems remains challenging. Here, we propose an interlayer coupling scheme to generate higher Chern numbers in a flat-band system, where the interlayer coupling transforms two C = 1 bands in a bilayer checkerboard lattice into a single flat band with C = 2 by lifting their degeneracy and merging their topological indices. Exact diagonalization calculation reveals that this engineered band hosts two fractional Chern insulator states with C = 2/3 and 2/5, respectively. An experimental setup is proposed to simulate these states using cold alkaline-earth-like atoms in an effective bilayer optical lattice. Our work provides a general and widely applicable strategy for constructing higher Chern number flat bands, opening a pathway to explore exotic fractional quantum phases.

cond-mat.str-el↗

arXiv2025

$\mathcal{PT}$-symmetric cavity magnomechanics with gain-assisted transparency and amplification

We investigate magnomechanically induced transparency in a parity-time-symmetric cavity magnomechanical system with traveling-field-induced non-Hermiticity. The setup consists of a microwave cavity mode coupled to magnons in a single-crystal yttrium iron garnet sphere, which in turn are hybridized with a vibrational mechanical mode through magnetostrictive interaction. In the Hermitian regime, strong photon-magnon coupling generates a single transparency window in the cavity transmission, which splits into a doublet when the magnon is coherently hybridized with the mechanical mode via magnomechanical coupling. This establishes a versatile platform in which the transparency spectrum can be engineered from single- to multi-window response using experimentally accessible, scaled magnomechanical interactions. When a non-Hermitian coupling is introduced, the system enters a parity-time-broken regime in which the transparency ceases to be purely passive and becomes gain assisted, leading to asymmetric transmission with amplification on one side of the resonance and enhanced absorption on the other. By tuning the cavity detuning, we convert magnomechanical transparency into Fano-type line shapes with strongly non-Lorentzian phase dispersion and map their deformation into asymmetric, gain-assisted Fano ridges in the joint space of probe and magnon detunings. Finally, we analyze the associated group delay and show that both slow- and fast-light behavior can be widely tuned by varying the photon-magnon and magnomechanical couplings together with the non-Hermitian strength, highlighting parity-time-symmetric cavity magnomechanics as a promising platform for reconfigurable quantum signal processing and enhanced sensing.

quant-ph↗

arXiv2025

Logarithmic light cone, slow entanglement growth, and quantum memory

Effective light cones, characterized by Lieb-Robinson bounds, emerge in nonrelativistic local quantum systems. Here, we present several analytical results derived from logarithmic light cones (LLCs). Possible origins of LLCs include the one-dimensional (1D) disordered XXZ model and a phenomenological model of many-body localization (MBL). In the LLC regime, we prove that, for arbitrary spatial dimensions and any initial pure state, entanglement growth is upper-bounded by logarithmic time with an additional subleading \emph{double-logarithmic} correction -- arising from a real asymptotic solution of the \emph{Lambert W} function -- valid up to the asymptotic time limit. In the context of the 1D disordered XXZ model, this result resolves the ambiguity in distinguishing between logarithmic and power-law fits of entanglement growth in numerical studies; we also propose a falsifiable phenomenological functional form for the entanglement growth that agrees with existing numerical results. We show that information scrambling is logarithmically slow in the LLC regime. Furthermore, we demonstrate that the LLC supports long-lived quantum memories -- quantum codes with macroscopic code distance and lifetimes that scale exponentially with system size -- under unitary time evolution. Our analytical results provide benchmarks for future numerical studies of the MBL regime at large time scales.

quant-ph↗

arXiv2025

Spin-Orbit Coupling-Driven Chirality Switching of Spin Waves in Altermagnets

Altermagnets host intrinsically chirality-splitting spin waves, which offer an ideal platform for chirality-based computing with low energy consumption and fast dynamics. However, achieving precise and efficient control over spin-wave chirality remains a challenge. Here, we propose a mechanism to switch the chirality of spin waves in altermagnets via electrically induced Rashba spin-orbit coupling (SOC), which is free of tuning external fields. For in-plane spin polarization, SOC introduces a splitting effect opposite to the altermagnetism, leading to spin inversion in the electronic energy bands and chirality reversal in the spin-wave dispersion. By tuning SOC strength, the chirality splitting of spin waves can be controllably modified, enabling chirality switching at fixed resonance conditions, which results in the reversal of transverse spin susceptibility. We further design an experimental setup based on an altermagnet/antiferromagnet heterostructure to realize this mechanism. Our work establish a pathway toward efficient electrical control of spin-wave chirality in altermagnets, facilitating the development of chirality-based spintronic devices.

cond-mat.mes-hall↗

arXiv2025

Non-Equilibrium Probing of Topological Supersolids in Spin-Orbit-Coupled Dipolar Condensates

A chiral supersolid is a quantum phase that simultaneously exhibits crystalline order, superfluidity, and topological spin texture, with spontaneously broken translational, U(1) gauge, and chiral symmetries. Here, we demonstrate a chiral supersolid with tunable non-equilibrium dynamics in a spin-orbit coupled dipolar Bose-Einstein condensate. By adjusting dipolar interaction and spin-orbit coupling, we uncover two distinct quantum phase transitions: (i) a first-order transition from a single skyrmion superfluid to a triangular meron supersolid, and (ii) a second-order transition from this superfluid to a square skyrmion supersolid. These phases are characterized by their lattice symmetries, nonclassical rotational inertia, and spin textures. Under parity-time symmetric dissipation, we predict phase-dependent damping of the current oscillations, directly linked to the superfluid fraction. The predicted chiral supersolid phase can be experimentally observed in ultracold magnetic atoms with spin-orbit coupling. Our results establish dipolar quantum gases as a platform for designing topological matter with spintronic functionality.

cond-mat.quant-gas↗

arXiv2025

Localization and Topology in Noncentrosymmetric Superconductors with Disorder

The celebrated Kitaev chain reveals a captivating phase diagram in the presence of various disorders, encompassing multifractal states and topological Anderson phases. In this work, we investigate the localization and topological properties of a dimerized topological noncentrosymmetric superconductor (NCS) under quasiperiodic and Anderson disorders. Using both global and local characterization methods, we identify energy-dependent transitions from ergodic to multifractal and localized states. Extended multifractal regimes emerge from the competition between dimerization, NCS order, and quasiperiodic modulation. This interplay causes localization to occur preferentially in different energy bands depending on the disorder strength, with the lowest bands exhibiting the highest sensitivity to parameter variations. We employ the real-space polarization method to compute the $\mathbb{Z}_2$ topological invariant, revealing alternating topological and trivial phases as the quasiperiodic potential increases, a behavior distinct from the typical topological Anderson phase diagram. Additionally, the topological states show remarkable robustness against Anderson disorder, providing new insights into topological phase stability in non-centrosymmetric systems. Finally, we propose a feasible experimental scheme based on superconducting Josephson junctions, where NCS-like behavior can be engineered via spatially modulated supercurrents. Our findings highlight the distinct roles of different disorder types in shaping localization and topology, providing insight into the engineering of Majorana zero modes and offering profound implications for topological quantum encryption schemes.

cond-mat.other↗

arXiv2025

Critical Behavior and Duality in Dimensionally Reduced Planar Chern-Simons Superconductors

Tha quantum electrodynamics of particles constrained to move on a plane is not a fully dimensionally reduced theory because the gauge fields through which they interact live in higher dimensions. By constraining the gauge field to the surface of the bulk, we obtain a fully reduced planar Abelian Chern-Simons Higgs model that can describe the vortex dynamics and second-order superconducting-normal phase transitions in planar Chern-Simons superconductors. Dual analyses performed before and after dimensional reduction yield the same Lagrangian for describing the vortex dynamics, indicating the self-consistency of our reduced theory. Compared to ordinary (2+1)-dimensional electrodynamics, we obtain anomalous fermion statistical vortices, consistent with results considering boundary effects. An additional electric charge constraint and different Chern-Simons parameter constraints are also found, which may help define a self-dual conformal field theory. Our renormalization group analysis shows that the quantized critical exponent depends on the Chern-Simons parameter. Quench disorder can bring more stable fixed points with different dynamical critical exponents. If we dimensionally reduce to a curved surface, our theory can also be extended to curved spacetimes, where geometric flow will be introduced and compete with vortex flow.

cond-mat.supr-con↗

arXiv2025

Exotic localization for the bound states in the non-reciprocal two-particle Hubbard model

We investigate the localization behavior of two-particle Hubbard model in the presence of non-reciprocal tunneling and non-Hermitian bound states can be obtained with strong repulsive interaction. Remarkably, the interaction induced bound state localization (BSL) can compete with non-Hermitian skin effect (NHSE) and give rise to diverse density profiles. Via the quantum scattering methods in the center of mass frame, the system can be mapped to an effective two dimensional (2D) lattice with the two-particle interaction contributing to a defective line. For the bound states of the largest eigen-energy, in contrast to the Hermitian cases, where the maximal localization center is pinned around the center of lattice, NHSE can lead to a faded diagonal line localization. For the unbound scattering states, unlike the single corner localization in the 2D Hatano-Nelson model, interaction can force the total localization to split into multiple centers. To make the system topological nontrivial, we further include terms taking the form of two-photon tunneling and the non-Hermitian photon bound pairs are also observed, which demonstrates a competition among NHSE, BSL and edge localization. Finally, we propose the experimental simulations via the platforms of electrical circuits. Our works shed light on the crossover study of quantum optics and non-Hermitian many body physics.

quant-ph↗

arXiv2024

Bounded light cone and robust topological order out of equilibrium

The ground state degeneracy of topologically ordered gapped Hamiltonians is the bedrock for self-correcting quantum memories, which are unfortunately not stable away from equilibrium even at zero temperature. This plague precludes practical robust self-correction since stability at zero temperature is a prerequisite for finite-temperature robustness. In this work, we show that the emergence of a bounded light cone renders the unitary time evolution a quasi-adiabatic continuation that preserves topological order, with the initial ground space retaining its macroscopic distance at all times as a quantum code. We also show how bounded light cones can emerge through suitable perturbations in Kitaev's toric code and honeycomb model. Our results suggest that topological orders and self-correcting quantum memories can be dynamically robust at zero temperature.

quant-ph↗

arXiv2024

Highly Scalable Quantum Router with Frequency-Independent Scattering Spectra

Optical quantum routers play a crucial role in quantum networks and have been extensively studied in both theory and experiment, leading to significant advancements in their performance. However, these routers impose stringent requirements for achieving desired routing results, as the incident photon frequency must be in strict resonance with one or several specific frequencies. To address this challenge, we propose an efficient quantum router scheme composed of semi-infinite coupled-resonator waveguide (CRW) and a giant atom. The single-channel router scheme enables stable output with 100% transfer rate over the entire energy band of the CRW. Leveraging this intriguing result, we further propose a multi-channel router scheme that possesses high stability and universality, while also being capable of performing various functionalities. The complete physical explanation of the underlying mechanism for this intriguing result is also presented. We hope that quantum router with output results unaffected by the frequency of the incoming information carriers presents a more reliable solution for the implementation of quantum networks.

quant-ph↗

arXiv2024

Spontaneous polarized phase transitions and symmetry breaking of an ultracold atomic ensemble in a Raman-assisted cavity

We investigate the ground-state properties and quantum phase transitions of an ensemble consisting of $N$ four-level atoms within an optical cavity coupled to the single cavity mode and external laser fields. The system is described by an extended imbalanced Dicke model, in which the co- and counterrotating coupling terms are allowed to have different coupling strengths. Some novel polarized phases characterized by the phase differences between the cavity field or the atomic spin excitation and the Raman laser are found analytically. Meanwhile, the full phase diagram and quantum phase transitions are also revealed. Finally, the breaking or restoration of the intrinsic symmetry in this system is addressed. It is found that besides the continuous $U(1)$ and discrete $\mathbb{Z}_2$ symmetries, the system also exhibits two reflection symmetries $σ_v$s, a central symmetry $C_2$ in the abstract position-momentum representation, and a discrete reflection parity-time ($\mathcal{PT}$) symmetry, a parameter exchange symmetry $\mathcal{T}_\mathrm{ex}$ in the parameters space. These additional symmetries are governed by two Coxeter groups.

quant-ph↗

arXiv2024

Two-dimensional topological effect in a transmon qubit array with tunable couplings

We investigate a square-lattice architecture of superconducting transmon qubits with inter-qubit interactions mediated by inductive couplers. Therein, the inductive couling between the qubit and couplers is suggested to be designed into the gradiometer form to intigimate the flux noise orginating from the environment. Via periodically modulating the couplers,the Abelian gauge potential, termed effective magnetic flux, can be synthesized artificially, making the system an excellent platform for simulating two-dimensional topological physics. In the simplest two-dimensional model, the double (or three-leg) ladder, the staggered vortex-Meissner phase transition different from that in the two-leg ladder can be found in the single-particle ground state as the effective magnetic flux varies. Besides, the large coupling ratio between the interleg and intraleg coupling strengths also makes the chiral current resemble squeezed sinusoidal functions. If the row number is further increased, the topological band structure anticipated at massive rows begins to occur even for a relatively small number of rows (ten or so for the considered parameters). This heralds a small circuit scale to observe the topological band. The edge state in the band gap is determined by the topological Chern number and can be calculated through integrating the Berry curvature with respect to the first Brillouin zone. Besides, we present a systematic method on how to measure the topological band structure based on time- and space-domain Frourier transformation of the wave function after properly excited. The result offers an avenue for simulating two-dimensional topological physics on the state-of-the-art superconducting quantum chips.

quant-ph↗

arXiv2024

Strange metal at the Lifshitz transition

Strange metal behavior is widely observed in cuprates, ruthenates, and twisted bilayer graphene. We study quantum critical transport at a two-dimensional Lifshitz transition, where the Fermi surface hosts a van Hove singularity and changes from convex to concave. Self-consistently solving the fermion-boson coupled system, we demonstrate a linear-in-$1/\omega$ optical conductivity driven by the interplay between impurity and critical scattering. The resistivity exhibits a persistent linear-in-$T$ in the quantum critical regime down to $T\rightarrow 0$. Spatially fluctuating Yukawa interaction further extends the linear-in-$T$ regime, providing a unified mechanism for strange metallic transport at the Lifshitz transition.

cond-mat.str-el↗