Superfluidity and spin superfluidity in spinor Bose gases

TL;DR

This paper demonstrates that spinor Bose gases with a quadratic Zeeman effect can exhibit both superfluidity and spin superfluidity, analyzing their interplay and proposing experimental methods to observe and distinguish these phenomena.

Contribution

It introduces a unified hydrodynamic framework for spin and mass supercurrents and proposes experimental setups to detect spin superfluidity in spinor Bose gases.

Findings

Spin and mass supercurrents can coexist and are driven by their respective chemical potential gradients.

A stationary state with counterflowing supercurrents can be achieved, canceling mass transport.

The timescale for coherent superfluid dynamics is an order of magnitude faster than incoherent dynamics.

Abstract

We show that spinor Bose gases subject to a quadratic Zeeman effect exhibit coexisting superfluidity and spin superfluidity, and study the interplay between these two distinct types of superfluidity. To illustrate that the basic principles governing these two types of superfluidity are the same, we describe the magnetization and particle-density dynamics in a single hydrodynamic framework. In this description spin and mass supercurrents are driven by their respective chemical potential gradients. As an application, we propose an experimentally accessible stationary state, where the two types of supercurrents counterflow and cancel each other, thus resulting in no mass transport. Furthermore, we propose a straightforward setup to probe spin superfluidity by measuring the in-plane magnetization angle of the whole cloud of atoms. We verify the robustness of these findings by evaluating the four-magnon collision time, and find that the time scale for coherent (superfluid) dynamics is separated from that of the slower incoherent dynamics by one order of magnitude. Comparing the atom and magnon kinetics reveals that while the former can be hydrodynamic, the latter is typically collisionless under most experimental conditions. This implies that, while our zero-temperature hydrodynamic equations are a valid description of spin transport in Bose gases, a hydrodynamic description that treats both mass and spin transport at finite temperatures may not be readily feasible.