Vortex lattices in binary Bose-Einstein condensates: Collective modes, quantum fluctuations, and intercomponent entanglement

TL;DR

This paper develops an effective field theory for binary Bose-Einstein condensates under synthetic magnetic fields, analyzing collective modes, quantum fluctuations, and entanglement, revealing how intercomponent interactions influence vortex lattice phases and entanglement properties.

Contribution

The study introduces renormalized coupling constants into an effective field theory, linking excitation spectra and entanglement characteristics under different magnetic field configurations.

Findings

Low-energy spectra are related by rescaling with renormalized constants.

Entanglement is stronger in parallel fields for repulsion and in antiparallel fields for attraction.

Quantum fluctuations significantly shift vortex lattice phase boundaries.

Abstract

We study binary Bose-Einstein condensates subject to synthetic magnetic fields in mutually parallel or antiparallel directions. Within the mean-field theory, the two types of fields have been shown to give the same vortex-lattice phase diagram. We develop an improved effective field theory to study properties of collective modes and ground-state intercomponent entanglement. Here, we point out the importance of introducing renormalized coupling constants for coarse-grained densities. We show that the low-energy excitation spectra for the two kindsof fields are related to each other by suitable rescaling using the renormalized constants. By calculating the entanglement entropy, we find that for an intercomponent repulsion (attraction), the two components are more strongly entangled in the case of parallel (antiparallel) fields, in qualitative agreement with recent studies for a quantum (spin) Hall regime. We also find that the entanglement spectrum exhibits an anomalous square-root dispersion relation, which leads to a subleading logarithmic term in the entanglement entropy. All of these are confirmed by numerical calculations based on the Bogoliubov theory with the lowest-Landau-level approximation. Finally, we investigate the effects of quantum fluctuations on the phase diagrams by calculating the correction to the ground-state energy due to zero-point fluctuations in the Bogoliubov theory. We find that the boundaries between rhombic-, square-, and rectangular-lattice phases shift appreciably with a decrease in the filling factor.