arXiv subjects

Yuan-Hong Chen

Publications and source records attributed to Yuan-Hong Chen.

4 recordsLinked to original sources

arXiv2026

Tuning Density and Spin Ordering of Degenerate Fermi Gases in an Optical Cavity

We investigate a spin-degenerate Fermi gas coupled to a high-finesse optical cavity, where the competition between scalar and vectorial couplings is controlled by the relative polarization angle of the pump and cavity fields. We find that the phase transition threshold is synergistically determined by the scalar-vectorial coupling weight and Pauli blocking, with the latter dictating the critical pump lattice depth required for the onset of superradiance. For a two-component Fermi gas with opposite spins, the population ratio drives two distinct types of phase transitions corresponding to real-space phase separation: continuous and discontinuous. Nevertheless, the boundary of the phase transition remains fundamentally governed by the scalar-vectorial coupling competition. We clarify the impact of the relative polarization angle on phase transitions of the system; these results also apply to bosonic systems. Our results provide valuable theoretical insights for future experimental realizations.

cond-mat.quant-gas↗

arXiv2025

Unified Field-integral Thermodynamics of Bose Mixtures: Stability and Critical Behavior

We establish a unified thermodynamic framework for Bose mixtures at finite temperatures based on the functional field integral, within which the decision on whether to discard the anomalous densities, when determining the density configuration and stability matrix, yields distinct theories. Beyond the existing Hartree-Fock approximation and Ota-Giorgini-Stringari theory, retaining the anomalous densities throughout will provide a completely self-consistent thermodynamic description, requiring the combination of the Hartree-Fock-Bogoliubov approximation and the representative statistical ensemble. Comparing three approaches for predicting magnetic susceptibility, we highlight the role of anomalous densities in stabilizing superfluid mixtures. We further unveil that Feshbach coupling can either expand the regime of atomic and molecular superfluids, or induce a phase transition to a pure molecular superfluid, depending on their density ratio. Importantly, we show that thermal fluctuations will trigger a phase transition from stable to unstable mixtures, where anomalous densities can serve as distinct signatures for experimental observation.

cond-mat.quant-gas↗

arXiv2025

Theoretical Exploration of Phase Transitions in a Cavity-BEC System with Two Crossed Optical Pumps

We consider a Bose-Einstein condensation (BEC) inside an optical cavity and two crossed coherent pump fields. We determine the phase boundary separating the normal superfluid phase and the superradiance phase, perturbatively. In the regime of negative cavity detuning, we map out the phase diagrams both for an attractive and a repulsive optical lattice. It turns out that the situation is quite different in two cases. Specifically, in the case of attractive lattice, if a system is in the superradiant phase with one pump laser, adding another pump does not drive the system out of the superradiance phase. While for the repulsive lattice, increasing another pump potential have suppressive effects on the superradiance. We also find that, in the case of attractive lattice, equally increasing two pump lattice potentials can induce a transition from the normal phase to the superradiance phase. In stark contrast, for the repulsive lattice, the system will remain in the normal phase as the pump depths are tuned within a wide range, independent of the cavity detuning and the decay rate.

cond-mat.quant-gas↗

arXiv2024

Quantum Triticality of Bosonic Atomic-Molecular Mixtures with Feshbach Coupling

We develop a functional integral formulation for a homogeneous bosonic atomic-molecular mixture with Feshbach coupling in three-spatial dimensions. Taking phase stability into account, we establish a rich ground-state phase diagram, which features three regions: molecular superfluid (MSF), atomic-molecular superfluid (AMSF), and phase separation (PS). The system can accommodate up to two tricritical points where the three regions meet, with one tricritical point being intrinsic and the other being conditional. Strikingly, we show that the sound velocity vanishes as the AMSF phase touches on the border of phase separation lines. We find that quantum fluctuations correction to the ground-state energy and quantum depletion of the condensates vary nonmonotonically with Feshbach coupling strength as well as molecular percentage. Correlation functions such as pairing amplitudes, density structure factor and spin density structure factor show characteristic behaviors when the system crosses phase transitions. Our work paves the way for future advancement toward understanding salient physics of atom-molecular mixtures.

cond-mat.quant-gas↗