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Optical Lattice Modulation Spectroscopy for Spin-orbit Coupled Bosons

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.