arXiv subjects

You-Qi Lu

Publications and source records attributed to You-Qi Lu.

4 recordsLinked to original sources

arXiv2026

Non-Hermiticity of an anomalous superradiant phase

We counterintuitively present a Hermitian squeezing-Dicke model as a minimal setting for non-Hermitian physics in many-body light-matter systems. It enables the realization of a non-Hermitian Hamiltonian of interest using a Hermitian quadratic bosonic system. Unlike previous dissipation-driven non-Hermitian mechanisms, effective parity-time ($\mathcal{PT}$) symmetry arises purely from squeezing and exchanges gainy and lossy eigenmodes. We identify non-Hermiticity of an anomalous superradiant phase for strong spins squeezing, exhibiting spontaneous breaking of the unique $\mathcal{PT}$ symmetry beyond $Z_2$ symmetries. Such exotic phase exhibits a complex excitation spectrum and undergoes a dynamical phase transition to a conventional superradiant phase at an exceptional point. An artificial magnetic field combined with the broken Hermiticity yields nonreciprocal dynamics with striking quantum amplification, exhibiting unidirectional enhanced transmission. Our Hermitian light-matter system offers an alternative pathway to exotic non-Hermitian physics and nonreciprocal quantum amplification.

quant-ph↗

arXiv2026

Anomalous topological superradiant phases

We present a novel set of light-matter topology realized by implementing a finite-component quantum Rabi array with a photonic analog of the Su-Schrieffer-Heeger (SSH) configuration. We demonstrate how complex light-matter couplings with species-dependent phases lead to the closure of superradiance-induced band gap in a manner that differs from that in the SSH model. We uncover an topological superradiant phase transition from a normal phase to a topological superradiant electromagnet phase, which is characterized both by a local order parameter and a global topological invariant. Novel superradiance-enhanced edge states emerge with significantly amplified excitations superior to those in topological normal phase. Strikingly, tuning light-atom coupling induces novel topological superradiant electric and magnetic phases, exhibiting chiral edge-mode excitation at opposite boundaries. Our proposed setup offers a tunable platform for topological quantum optics, advancing applications in topological superradiant lasers.

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arXiv2024

Quantum tricriticality and universal scaling in a tricritical quantum Rabi system

Quantum tricriticality, a unique form of high-order criticality, is expected to exhibit fascinating features including unconventional critical exponents and universal scaling laws. However, a quantum tricritical point (QTCP) is much harder to access, and the corresponding phenomena at tricriticality have rarely been investigated. In this study, we explore a tricritical quantum Rabi model, which incorporates a nontrivial parameter for adjusting the coupling ratio between a cavity and a three-level atom. The QTCP emerges at the intersection of a first- and second-order superradiant phase transitions according to Landau theory. By using finite-frequency scaling analyses for quantum fluctuations and the mean photon number, universal critical exponents differentiate the QTCP from the second-order critical point. We find that the phase transition at the tricritical point goes beyond the conventional second-order phase transition. Our work explores an interesting direction in the generalization of the well-known Rabi model for the study of higher-order critical points due to its high control and tunability.

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arXiv2021

Extended Dicke quantum battery with interatomic interactions and driving field

We investigate the charging process of quantum battery (QB) systems in an extended Dicke model with both atomic interactions and an external driving field. We focus on the effects of the atomic interaction and the external driving field on the charging performance of QB and find that the maximum stored energy of QB has a critical phenomenon. We analyze the critical behavior and obtain the analytical expression of the critical atomic interaction. The dependence of the maximum stored energy, the energy quantum fluctuations and the maximum charging power on the number $N$ of the two-level systems are also discussed. In particular, for the maximum charging power, we obtain the quantum advantage of the QB, which approximately satisfies a superlinear scaling relation $P_{max}\propto N^α$, where scaling exponent $α$ varies with the number $N$ of the two-level systems. In the ultra-strong coupling regime, the atomic interaction can lead to a faster battery charging, and the quantum advantage $α= 1.88$ can be achieved. While in the deep-strong coupling regime, the quantum advantage of the QB's maximum charging power is the same as that of the Dicke QB, i.e., $α=1.5$.

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