Excitations of Bose-Einstein condensates in optical lattices

TL;DR

This paper investigates excitations in Bose-Einstein condensates within optical lattices near the superfluid-insulator transition, proposing a robust local diagnostic based on atom number variance that aligns with experimental observations.

Contribution

It introduces a new diagnostic method using atom number variance to study excitations and coherence changes in optical lattice systems, applicable across various lattice fillings.

Findings

Number variance increases indicate excitations and coherence loss.

Results agree with recent experimental data.

Spectral features vary with perturbation duration, revealing atom dynamics.

Abstract

In this paper we examine the excitations observable in atoms confined in an optical lattice around the superfluid-insulator transition. We use increases in the number variance of atoms, subsequent to tilting the lattice as the primary diagnostic of excitations in the lattice. We show that this locally determined quantity should be a robust indicator of coherence changes in the atoms observed in recent experiments. This was found to hold for commensurate or non-commensurate fillings of the lattice, implying our results will hold for a wide range of physical cases. Our results are in good agreement with the quantitative factors of recent experiments. We do, howevers, find extra features in the excitation spectra. The variation of the spectra with the duration of the perturbation also turns out to be an interesting diagnostic of atom dynamics.