Quantum phases and spectrum of collective modes in a spin-1 BEC with spin-orbital-angular-momentum coupling

TL;DR

This paper studies the low-energy excitations and phase structure of spin-1 Bose-Einstein condensates with spin-orbital-angular-momentum coupling, revealing phase transitions, hybridized modes, and dynamical behaviors.

Contribution

It provides the first detailed analysis of collective modes and phase boundaries in SOAM-coupled spin-1 BECs, including vortex states and excitation spectra.

Findings

Discontinuous changes in angular momentum and magnetization at phase boundaries.

Hybridization of spin and density modes in the excitation spectrum.

Confirmation of spectrum features through dynamical evolution and variational analysis.

Abstract

Motivated by the recent experiments [Chen et al., Phys. Rev. Lett 121, 113204 (2018), Chen et al., Phys. Rev. Lett. 121, 250401 (2018)], we investigate the low-lying excitation spectrum of the ground-state phases of spin-orbital-angular-momentum-coupled (SOAM-coupled) spin-1 condensates.At vanishing detuning, a ferromagnetic SOAM-coupled spin-1 BEC can have two ground-state phases, namely coreless and polar-core vortex states, whereas an antiferromagnetic BEC supports only polar-core vortex solution. The angular momentum per particle, longitudinal magnetization, and excitation frequencies display discontinuities across the phase boundary between the coreless vortex and polar-core vortex phases. The low-lying excitation spectrum evaluated by solving the Bogoliubov-de-Gennes equations is marked by avoided crossings and hence the hybridization of the spin and density channels. The spectrum is further confirmed by the dynamical evolution of the ground state subjected to a perturbation suitable to excite a density or a spin mode and a variational analysis for the density-breathing mode.