Counterflow and paired superfluidity in one-dimensional Bose mixtures in optical lattices

TL;DR

This paper investigates quantum phases of one-dimensional Bose mixtures in optical lattices, identifying superfluid and charge density wave phases, and proposes experimental detection methods using time-of-flight images, structure factors, Feshbach ramps, and Bragg spectroscopy.

Contribution

It combines Tomonaga-Luttinger liquid theory and TEBD simulations to map phase boundaries and suggests experimental techniques to detect paired and counterflow superfluid phases.

Findings

Identification of paired and counterflow superfluid phases.

Coexistence of superfluid and charge density wave order.

Experimental protocols for phase detection

Abstract

We study the quantum phases of mixtures of ultra-cold bosonic atoms held in an optical lattice that confines motion or hopping to one spatial dimension. The phases are found by using Tomonaga-Luttinger liquid theory as well as the numerical method of time evolving block decimation (TEBD). We consider a binary mixture with repulsive intra-species interactions, and either repulsive or attractive inter-species interaction. For a homogeneous system, we find paired- and counterflow-superfluid phases at different filling and hopping energies. We also predict parameter regions in which these types of superfluid order coexist with charge density wave order. We show that the Tomonaga-Luttinger liquid theory and TEBD qualitatively agree on the location of the phase boundary to superfluidity. We then describe how these phases are modified and can be detected when an additional harmonic trap is present. In particular, we show how experimentally measurable quantities, such as time-of-flight images and the structure factor, can be used to distinguish the quantum phases. Finally, we suggest applying a Feshbach ramp to detect the paired superfluid state, and a $\pi/2$ pulse followed by Bragg spectroscopy to detect the counterflow superfluid phase.