Optical Lattice Modulation Spectroscopy for Spin-orbit Coupled Bosons

TL;DR

This paper proposes an optical lattice modulation spectroscopy method to detect and distinguish superfluid and Mott insulator phases, as well as different superfluid phases, in spin-orbit coupled bosonic systems.

Contribution

It introduces a novel spectroscopy technique to identify quantum phases and excitations in spin-orbit coupled bosons in optical lattices.

Findings

Distinct momentum distribution patterns differentiate phases.

Spectroscopy can identify Goldstone and Higgs modes.

Method distinguishes zero-momentum and twisted superfluid phases.

Abstract

Interacting bosons with two "spin'' states in a lattice show novel superfluid-insulator phase transitions in the presence of spin-orbit coupling. Depending on the parameter regime, bosons in the superfluid phase can condense to either a zero momentum state or to one or multiple states with finite momentum, leading to an unconventional superfluid phase. We study the response of such a system to modulation of the optical lattice potential. We show that the change in momentum distribution after lattice modulation shows distinct patterns in the Mott and the superfluid phase and these patterns can be used to detect these phases and the quantum phase transition between them. Further, the momentum resolved optical modulation spectroscopy can identify both the gapless (Goldstone) gapped amplitude (Higgs) mode of the superfluid phase and clearly distinguish between the superfluid phases with a zero momentum condensate and a twisted superfluid phase by looking at the location of these modes in the Brillouin zone. We discuss experiments which can test our theory.