Optical lattice influenced geometry of quasi-2D binary condensates and quasiparticle spectra

TL;DR

This paper investigates how optical lattices affect the geometry and quasiparticle spectra of two-species Bose-Einstein condensates, revealing unique spectral behaviors during phase separation.

Contribution

It introduces a detailed analysis of quasiparticle spectra and ground state geometry of TBECs in optical lattices using coupled nonlinear equations and HFB theory.

Findings

Quasiparticle energies soften near phase separation

Energies harden after phase separation occurs

Mode degeneracies are lifted post phase separation

Abstract

We explore the collective excitations of optical lattices filled with two-species Bose-Einstein condensates (TBECs). We use a set of coupled discrete nonlinear Schr\"odinger equations to describe the system, and employ Hartree-Fock-Bogoliubov (HFB) theory with the Popov approximation to analyze the quasiparticle spectra at zero temperature. The ground state geometry, evolution of quasiparticle energies, structure of quasiparticle amplitudes, and dispersion relations are examined in detail. The trends observed are in stark contrast to the case of TBECs only with a harmonic confining potential. One key observation is the quasiparticle energies are softened as the system is tuned towards phase separation, but harden after phase separation and mode degeneracies are lifted.