Excitation Spectra of Bose–Einstein Condensates in Optical Lattice

Abstract

The excitation spectra of Bose–Einstein condensates are investigated in a three-dimensional optical lattice by the Bogoliubov theory considering the original sinusoidal potential for the optical lattice. When the lattice potential becomes high, the excitations show softening at large wavelengths, suggesting the breakdown of superfluidity. We also study the filling and interaction dependences of the properties of the excitation spectra and one-dimensional lattice case.