arXiv subjects

Qing-Dong Jiang

Publications and source records attributed to Qing-Dong Jiang.

At least 19 recordsLinked to original sources

arXiv2026

Distinct Spatiotemporal Dynamics of Thermoelectric Transport Across Superconducting Transition

We investigate the relaxation dynamics of heat transport in superconductors, shaped by the interplay of diffusion, nonlinearity, and magnetic fields. Focusing on regimes near the critical temperature Tc, we analyze two classes of relaxation diffusion equations that give rise to qualitatively distinct dynamics, which we denote as Type I (linear) and Type II (nonlinear). Type I relaxation, characteristic of the normal state above Tc, results in a steady and spatially uniform heat current governed by linear diffusion. By contrast, Type II relaxation, relevant below Tc, exhibits non steady dynamics marked by pronounced spatial inhomogeneities and an evolving pattern, in which an initially localized hot spot propagates transiently through the system. The striking distinction between these regimes underscores a fundamental shift in transport mechanisms across the superconducting phase transition and provides experimentally relevant predictions in light of emerging techniques for probing local dissipation.

cond-mat.supr-con↗

arXiv2026

No-Go Theorem and Routes towards Cavity-Enhanced Superconductivity

Recent experiments reporting cavity-vacuum-modified superconductivity raise a fundamental question: under what conditions can vacuum electromagnetic fluctuations increase a superconducting transition temperature? Starting from a Ginzburg--Landau theory minimally coupled to a quantized cavity mode, we derive the cavity-induced renormalization of the superconducting free energy. This correction comprises a positive diamagnetic contribution and a negative paramagnetic exchange contribution. We prove that, in a passive cavity, the latter cannot exceed the former, establishing a no-go theorem: within minimal cavity electrodynamics, vacuum fluctuations suppress, rather than enhance, superconductivity. We then identify two routes beyond this constraint, both involving additional collective degrees of freedom. In the collective-mode route, a cavity-active excitation amplifies the attractive paramagnetic contribution. In the competing-order route, the cavity weakens an order that competes with superconductivity, thereby indirectly enhancing superconductivity. Together, these results turn the no-go theorem into a practical design principle: cavity superconductivity enhancement requires an additional cavity-coupled material mode that either strengthens paramagnetic exchange or suppresses a competing order.

cond-mat.supr-con↗

arXiv2026

Multipolar Light-Matter Hamiltonians in Symmetry-Breaking Photonic Vacuums

We show that the conventional multipolar Hamiltonian is qualitatively modified when the photonic vacuum breaks inversion or time-reversal symmetry. By explicitly applying the Power-Zienau-Woolley transformation, we derive the resulting multipolar Hamiltonians for two idealized chiral photonic environments: a spatial-chiral vacuum, which breaks inversion symmetry, and a temporal-chiral vacuum, which breaks time-reversal symmetry. In the spatial-chiral case, the transformation generates an inversion-breaking self-energy, whereas in the temporal-chiral case it produces an additional Zeeman-like energy. Using a trapped hydrogen-like atom and a charged harmonic oscillator in cavities as minimal examples, we show that these symmetry-dependent terms lead to characteristic spectral shifts. Our work provides a general framework for describing light-matter interactions in chiral quantum electrodynamics and identifying the associated symmetry-dependent effects on cavity-embedded atoms, molecules, and quantum materials.

quant-ph↗

arXiv2026

A field theory approach to Breit-type Hamiltonians in gapped Dirac systems

We develop a path-integral-based field theory for deriving Breit-type low-energy Hamiltonians for gapped Dirac systems coupled to both vector and axial gauge fields. Treating the mass gap as the large energy scale, we integrate out the high-energy component of the Dirac spinor and obtain a canonical Schrödinger description for the remaining low-energy degrees of freedom. For the ordinary Dirac equation, our method reproduces the conventional Breit Hamiltonian order by order. In the presence of axial gauge fields, however, the resulting Hamiltonian contains additional vector-axial couplings that have no analogue in the traditional electromagnetic case. We illustrate the method using three- and two-dimensional Dirac models and discuss its relevance to gapped Weyl systems, where dynamical axial fields can generate distinctive low-energy transport signatures.

cond-mat.mes-hall↗

arXiv2026

Sound Induced Hall Currents in Weyl Exciton Insulators

Weyl semimetals exhibit anomalous transport controlled by their gapless chiral nodes, while gapped Weyl systems are often expected to lose such distinctive responses. Here we show that Weyl excitonic insulators instead host a new form of axial-field-driven transport that exists only in the massive phase. Starting from the low-energy Breit-type Hamiltonian for a gapped Weyl system coupled to strain-induced axial potentials, we develop a semiclassical wave-packet theory and identify a dissipative transverse current generated by a dynamical axial potential. This response is qualitatively distinct from both ordinary vector-potential transport in gapped systems and axial responses in gapless Weyl semimetals. Physically, it originates from a mass-induced Berry structure of the reconstructed Weyl bands, which becomes active when the system is driven out of equilibrium by a chiral chemical-potential imbalance. We show that transverse sound waves provide a natural route to generate the required dynamical axial field and estimate the resulting current for realistic material parameters. Our results reveal sound-induced Hall transport as a direct probe of Weyl excitonic order and provide a transport signature of interaction-generated mass in Weyl materials.

cond-mat.mes-hall↗

arXiv2026

Fermion-mediated Casimir effect on mesoscopic rings implementing non-Clifford SWAP$^α$ gates

The Casimir effect is typically governed by intrinsic material properties and lacks in situ tunability. We show that, in mesoscopic rings, both the magnitude and sign of the fermion-mediated Casimir interaction can be controlled via the Aharonov-Bohm effect. The resulting interplay between the Aharonov-Bohm phase and the Casimir interaction provides a route to engineer long-range interactions. In particular, this mechanism enables the implementation of non-Clifford SWAP$^α$ gates between spatially separated spin qubits, thereby reducing the overhead for universal quantum computation and quantum error correction in spin-qubit architectures.

cond-mat.mes-hall↗

arXiv2026

Quantum Hall Liquids Coupled to Dynamical Electromagnetism

We investigate the effect on a Quantum Hall (QH) liquid of its coupling to 3+1 dimensional dynamical electromagnetism, which renders the system gapless. We calculate both the Hall and longitudinal resistances, $ρ_H$ and $ρ_L$, in the context of a minimal model of the electromagnetic environment, with a small three dimensional conductivity ${\tildeσ}$, that allows for a counter-flow current. In the thermodynamic limit, we show that $ρ_H$ is quantized, while $ρ_L$ approaches a non-zero limit, $ρ_L \sim α\, R_K$, where $α$ and $R_K=2π/e^2$ are the fine structure and the Klitzing constant. In contrast, the QH conductance, $σ_H$, is smaller than the expected quantized value by a correction $\sim α^2/R_K$. The electromagnetic interaction also generates corrections of order $α^2$ to the quasiparticle charges and statistics, in a way that is consistent with general arguments based on gauge invariance. In addition, we present an intuitive argument that relates the flux attachment associated with the composite boson representation of the electron liquid to the empirically observed %persistence of approximate quantization of $ρ_H$, even in circumstances in which $ρ_L$, and the deviation of $σ_H$ from its quantized value, are substantial.

cond-mat.mes-hall↗

arXiv2026

Nonreciprocal perfect Coulomb drag in electron-hole bilayers: coherent exciton superflow as a diode

Distinguishing an exciton condensate from an excitonic gas or insulator remains a fundamental challenge, as both phases feature bound electron-hole pairs but differ only by the emergence of macroscopic phase coherence. Here, we theoretically propose that a spin-orbit-coupled bilayer system can host a finite-momentum exciton condensate exhibiting a nonreciprocal perfect Coulomb drag -- the coherent-exciton diode effect. This effect arises from the simultaneous breaking of inversion and time-reversal symmetries in the exciton condensate, resulting in direction-dependent critical counterflow currents. The resulting nonreciprocal perfect Coulomb drag provides a clear and unambiguous transport signature of phase-coherent exciton condensation, offering a powerful and experimentally accessible approach to identify, probe, and control exciton superfluidity in solid-state platforms.

cond-mat.mes-hall↗

arXiv2026

Vacuum Torque Without Anisotropy: Switchable Casimir Torque Between Altermagnets

Casimir torque is conventionally associated with explicit breaking of rotational symmetry, arising from material dielectric anisotropy, geometric asymmetry, or externally applied fields that themselves break rotational invariance. Here we demonstrate a fundamentally different mechanism: an axially symmetric magnetic field can generate a Casimir torque by inducing an axially asymmetric Casimir energy - and can even reverse the torque's sign. Focusing on two-dimensional altermagnets, we show that a magnetic field applied perpendicular to the plane - while preserving in-plane rotational symmetry - activates an orientation-dependent vacuum interaction through the combined crystalline symmetry $\mathrm{C_n T}$ inherent to altermagnetic order. The resulting torque emerges continuously and scales quadratically with the magnetic field strength. We further analyze its temperature and distance dependence, revealing scaling behaviors that are qualitatively different from those found in uniaxial bulk materials. Our results identify time-reversal symmetry breaking as a powerful route for engineering both the sign and strength of Casimir torque and establish altermagnets as an exciting platform for exploring phenomena driven by vacuum quantum fluctuations.

quant-ph↗

arXiv2025

Harnessing Vacuum Fluctuations to Shape Electronic and Photonic Behavior

Vacuum quantum fluctuations are an inescapable and fundamental feature of modern physics. By integrating cavity-enhanced or surface-modified vacuum quantum fluctuations with low-dimensional materials, a new paradigm-vacuumronics-emerges, enabling unprecedented control over both material properties and photonic responses at the micro- and nanoscale. This synergy opens novel pathways for engineering quantum light-matter interactions, advancing applications in quantum photonics, nanoscale optoelectronics, and quantum material design.

cond-mat.mes-hall↗

arXiv2025

Cavity-Vacuum-Induced Chiral Spin Liquids in Kagome Lattices: Tuning and Probing Topological Quantum Phases via Cavity Quantum Electrodynamics

Topological phases in frustrated quantum magnetic systems have captivated researchers for decades, with the chiral spin liquid (CSL) standing out as one of the most compelling examples. Featured by long-range entanglement, topological order, and exotic fractional excitations, the CSL has inspired extensive exploration for practical realizations. In this work, we demonstrate that CSLs can emerge in a kagome lattice driven by vacuum quantum fluctuations over the non-interacting vacuum within a single-mode gyrotropic cavity. The gyrotropic cavity imprints quantum fluctuations with time-reversal symmetry breaking and stabilizes a robust CSL phase without external laser excitation. Moreover, we identify experimentally accessible observables -- such as average photon number and transport properties -- that reveal connections between photon dynamics and the emergent chiral order. Our findings establish a novel pathway for creating, controlling, and probing topological and symmetry-breaking quantum phases in strongly correlated systems.

cond-mat.str-el↗

arXiv2025

Searching Repulsive Casimir Forces Between Magneto-Electric Materials

The Casimir effect, arising from vacuum quantum fluctuations, plays a fundamental role in the development of modern quantum electrodynamics. In parallel, the field of condensed matter has flourished through the discovery of various materials exhibiting broken symmetries, often connected to topology and characterized by magneto-electric coupling. To enhance the comprehension of the role of parity symmetry and time-reversal symmetry in determining the sign of the Casimir force, we calculate the Casimir forces between magneto-electric materials and obtain a phase diagram governing the sign of symmetry-breaking-induced Casimir forces. We also investigate how the force phase diagram varies with the separation distances between the objects. Our results contribute to a better understanding of the sign of the Casimir force, a subject bearing both theoretical interest and practical significance.

quant-ph↗

arXiv2025

Angular Momentum-Dependent Spectral Shift in Chiral Vacuum Cavities

Based on a hybrid light-matter unitary transformation for cavity quantum electrodynamics, we investigate the spectral shift of an atom induced by quantum fluctuations in a chiral vacuum cavity. Remarkably, we find an intriguing angular momentum-dependent shift in the spectra of bound states. Our approach shows promise in going beyond traditional perturbative methods and demonstrates effectiveness even in the strong-coupling limit, as evidenced by our numerical benchmarks in the case of a two-dimensional quantum harmonic oscillator. In addition, we establish a cavity-interaction picture for calculating the chiral vacuum Rabi oscillation in the strong-coupling limit for a generic central potential. The anomalous spectral shift revealed in this study possesses both fundamental and practical significance and could be readily observed in experiments.

quant-ph↗

arXiv2025

Quantum Hall effect in a chiral cavity

We investigate the influence of quantum fluctuations in a chiral cavity on the quantum Hall (QH) state, extending previous studies of QH liquids in linearly polarized cavities. Using the Schrieffer-Wolff transformation for perturbative cavity-matter interaction, we identify the system's normal modes, which correspond to the elementary excitations of the dressed electrons and photons. In contrast to the linear case, we find that the chiral cavity modifies the Kohn mode frequency by a contribution proportional to the cyclotron frequency, which can be interpreted as a renormalization of the magnetic field by cavity fluctuations. We show that the AC conductivities display cavity-induced corrections, including an isotropic quantum reactance effect and a rotating total-current response under applied AC fields. These findings are also derived from a hydrodynamic approach, which extends their validity to fractional quantum Hall states. Finally, we examine the role of finite cavity quality factor and find that while photon losses introduce resistive contributions to the impedance, these vanish in the DC limit. Our results provide insights into the interplay between quantum Hall states and chiral cavities, with significant implications for material engineering and cavity-induced topological effects.

cond-mat.mes-hall↗

arXiv2025

Non-Hermitian wave-packet dynamics and its realization within a non-Hermitian chiral cavity

Topological wave-packet dynamics provide a powerful framework for studying quantum transport in topological materials. However, extending this approach to non-Hermitian quantum systems presents several important challenges, primarily due to ambiguities in defining the Berry phase and the non-unitary evolution of the wave-packets when $\mathcal{P}\mathcal{T}$ symmetry is broken. In this work, we adopt the complex Berry phase definition using the bi-orthogonal formalism and derive the semiclassical equations of motion (EOM) for a wave-packet in a non-Hermitian topological system. Interestingly, we find that the complex Berry curvature introduces both an anomalous velocity and an anomalous force into the semiclassical EOM. To validate the derived EOM, we design a non-Hermitian Haldane model featuring non-reciprocal next-nearest-neighbor (NNN) hopping, where the imbalance in the NNN hopping amplitudes gives rise to an emergent `complex chirality'. We reveal that the real and imaginary components of the complex chirality dictate the signs of both the real and imaginary parts of the complex Berry curvature, as well as the direction and dissipation rate of the edge states. Our analytical findings are confirmed by direct numerical simulations of the wave-packet dynamics. Finally, we suggest a potential experimental realization of this complex Haldane model using a non-Hermitian optical chiral cavity, providing a promising platform for testing our theoretical predictions.

cond-mat.mes-hall↗

arXiv2025

Cavity Quantum Hall Hydrodynamics

Motivated by recent experiments, we study the coupling of quantum Hall (QH) hydrodynamics to quantum electrodynamics (QED) within a resonance cavity. In agreement with experimental observations, we find that the Hall conductivity remains unchanged. However, the coupling to the cavity induces a second-order quantum reactance effect, contributing distinctly to the longitudinal AC conductivity. This effect arises from the exchange of energy between the QH fluid and cavity photons. Beyond the topological response, we show that the cavity couples to collective excitations, resulting in a shift of the Kohn mode frequency. Our methods are broadly applicable to both integral and fractional QH liquids, and our results offer a universal perspective on the protection of topological properties against long-range interactions induced by electromagnetic cavity modes.

cond-mat.mes-hall↗

arXiv2024

Engineering Ponderomotive Potential for Realizing $π$ and $π/2$ Bosonic Josephson Junctions

We study the ponderomotive potential of a bosonic Josephson junction periodically modulated by a high-frequency electromagnetic field. Within the small population difference approximation, the ponderomotive drive induces the well-known Kapitza pendulum effect, stabilizing a $π$-phase mode. We discuss the parameter dependence of the dynamical transition from macroscopic quantum self-trapping to $π$-Josephson oscillations. Furthermore, we examine the situation where the small population difference approximation fails. In this case, an essential momentum-shortening effect emerges, leading to a stabilized $π/2$-phase mode under certain conditions. By mapping this to a classical pendulum scenario, we highlight the uniqueness and limitations of the $π/2$-phase mode in bosonic Josephson junctions.

cond-mat.quant-gas↗

arXiv2024

Geometry Dynamics in Chiral Superfluids

We investigate the geometric response of chiral superfluids when coupled to a dynamic background geometry. We find that geometry fluctuations, represented by the flexural mode, interact with the superfluid phase fluctuations (the Goldstone mode). Starting from a minimally coupled theory, we derive the equilibrium conditions for a static background defined by supercurrent, curvature, and tension, and then obtain linearized equations for the propagation of the Goldstone and flexural modes. The equations reveal distinctive chirality-dependent effects in the propagation of the flexural mode. Specifically, a background supercurrent induces a chiral drag effect, localizing flexural waves at the superfluid boundary, while background curvature introduces anisotropic corrections to the superfluid phase and group velocities, as well as a tension in the flexural mode dispersion. Furthermore, curvature couples flexural and phase modes into dressed excitations, with tilted Dirac cones along the principal curvature directions. These effects provide dynamical signatures of the formation of a chiral condensate, and can be tuned by manipulating the background geometry.

cond-mat.quant-gas↗