arXiv subjects

Xiong-jun Liu

Publications and source records attributed to Xiong-jun Liu.

6 recordsLinked to original sources

arXiv2026

Experimental engineering of Floquet topological phases in a one-dimensional optical lattice

Periodic driving enables realization of topological phases without static counterparts. We experimentally realize and detect a one-dimensional anomalous Floquet topological phase in an optical lattice, using multi-frequency control to manipulate the relative sign structure of the gap windings $(W_0,W_\pi)$ associated with the $0$ and $\pi$ quasienergy gaps. We develop a lattice-depth modulation scheme that induces staggered nearest-neighbor $s$-$p$ orbital couplings and realize a minimal nontrivial Floquet topology under single-tone driving. Introducing a second tone, its relative phase controls the effective coupling signs in the $0$ and $\pi$ gaps, thereby tuning the corresponding windings to add and produce a high-winding phase or to cancel while retaining nontrivial gap indices. We read out $(W_0,W_\pi)$ with a band-inversion-surface (BIS)-resolved Ramsey protocol assisted by lattice-position shaking, which measures relative Floquet phases on the BISs. Controlled quenches further confirm phase-dependent band modifications even at quasimomenta far from resonance. These results establish multi-frequency control with a tunable relative phase as a quantitative route to engineering anomalous Floquet topology, and demonstrate phase-coherent coexistence of distinct drive modalities.

cond-mat.quant-gas↗

arXiv2025

A Radio-Frequency Emitter Design for the Low-Frequency Regime in Atomic Experiments

Radio-frequency (RF) control is a key technique in cold atom experiments. We present a compact and efficient RF circuit based on a capacitive transformer network, where a low-frequency coil operating up to 30MHz serves as both an intrinsic inductor and a power-sharing element. The design enables high current delivery and flexible impedance matching across a wide frequency range. We integrate both broadband and narrowband RF networks into a unified configuration that overcomes the geometric constraints imposed by the metallic chamber. In evaporative cooling, the broadband network allows a reduction of the applied RF input power from 14.7dBW to -3.5dBW, owing to its non-zero coil current even at ultra-low frequencies. This feature enables the Bose-Fermi mixture to be cooled below 10{\mu}K. In a Landau-Zener protocol, the coil driven by the narrowband network transfers 80% of rubidium atoms from |F = 2,mF = 2> to |2,-2> in 1 millisecond, achieving a Rabi frequency of approximately 9 kHz at an input power of 0.1dBW.

physics.atom-ph↗

arXiv2021

Duality between two generalized Aubry-Andre models with exact mobility edges

A mobility edge (ME) in energy separating extended from localized states is a central concept in understanding various fundamental phenomena like the metal-insulator transition in disordered systems. In one-dimensional quasiperiodic systems, there exist a few models with exact MEs, and these models are beneficial to provide exact understanding of ME physics. Here we investigate two widely studied models including exact MEs, one with an exponential hopping and one with a special form of incommensurate on-site potential. We analytically prove that the two models are mutually dual, and further give the numerical verification by calculating the inverse participation ratio and Husimi function. The exact MEs of the two models are also obtained by calculating the localization lengths and using the duality relations. Our result may provide insight into realizing and observing exact MEs in both theory and experiment.

cond-mat.dis-nn↗

arXiv2021

Many-body critical phase: extended and nonthermal

The transition between ergodic phase and many-body localization (MBL) phase lies at the heart in understanding quantum thermalization of many-body systems. Here we predict a many-body critical phase in the one-dimensional extended Aubry-André-Harper-Hubbard model, which is different from both the ergodic phase and MBL phase, implying that the quantum system hosts three different fundamental phases. It is shown that the level statistics in the many-body critical phase are well characterized by the so-called critical statistics, and the wave functions in this phase generally exhibit a multifractal behavior. We further study the half-chain entanglement entropy (EE) and thermalization properties by exact diagonalization, which show that the EE in this critical phase manifest a volume law EE scaling while the many-body states violate the eigenstate thermalization hypothesis. This work unveils a novel many-body phase which is extended but non-ergodic.

cond-mat.dis-nn↗

arXiv2019

Localization driven superradiant instability

The prominent Dicke superradiant phase arises from coupling an ensemble of atoms to cavity optical field when external optical pumping exceeds a threshold strength. Here we report a prediction of the superrandiant instability driven by Anderson localization, realized with a hybrid system of Dicke and Aubry-Andre (DAA) model for bosons trapped in a one-dimensional (1D) quasiperiodic optical lattice and coupled to a cavity. Our central finding is that for bosons condensed in localized phase given by the DAA model, the resonant superradiant scattering is induced, for which the critical optical pumping of superradiant phase transition approaches zero, giving an instability driven by Anderson localization. The superradiant phase for the DAA model with or without a mobility edge is investigated, showing that the localization driven superradiant instability is in sharp contrast to the superradiance as widely observed for Bose condensate in extended states, and should be insensitive to temperature of the system. This study unveils an insightful effect of localization on the Dicke superradiance, and is well accessible based on the current experiments.

cond-mat.quant-gas↗

arXiv2017

New Group V Elemental Bilayers: A Tunable Structure Model with 4,6,8-atom Rings

Two-dimensional (2D) group V elemental materials have attracted widespread attention due to their nonzero band gap while displaying high electron mobility. Using first-principles calculations, we propose a series of new elemental bilayers with group V elements (Bi, Sb, As). Our study reveals the dynamical stability of 4, 6, and 8-atom ring structures, demonstrating their possible coexistence in such bilayer systems. The proposed structures for Sb and As are large-gap semiconductors that are potentially interesting for applications in future nanodevices. The Bi structures have nontrivial topological properties with a large and direct nontrivial band gap. The nontrivial gap is shown to arise from a band inversion at the Brillouin zone center due to the strong intrinsic spin-orbit coupling (SOC) in Bi atoms. Moreover, we demonstrate the possibility to tune the properties of these materials by enhancing the ratio of 6-atom rings to 4 and 8-atom rings, which results in wider nontrivial band gaps and lower formation energies.

cond-mat.mtrl-sci↗