Superfluid drag in the two-component Bose-Hubbard model

Abstract

In multicomponent superfluids and superconductors, co-and counter-flows of components have in general different properties. It was discussed in 1975 by Andreev and Bashkin, in the context of He 3 /He 4 superfluid mixtures, that inter-particle interactions produce a dissipationless drag. The drag can be understood as a superflow of one component induced by phase gradients of the other component. Importantly the drag can be both positive (entrainment) and negative (counter-flow). The effect is known to be of crucial importance for many properties of diverse physical systems ranging from the dynamics of neutron stars, rotational responses of Bose mixtures of ultra-cold atoms to magnetic responses of multicomponent superconductors. Although there exists a substantial literature that includes the drag interaction phenomenologically, much fewer regimes are covered by quantitative studies of the microscopic origin of the drag and its dependence on microscopic parameters. Here we study the microscopic origin and strength of the drag interaction in a quantum system of two-component bosons on a lattice with short-range interaction. By performing quantum Monte-Carlo simulations of a two-component Bose-Hubbard model we obtain dependencies of the drag strength on the boson-boson interactions and properties of the optical lattice. Of particular interest are the strongly-correlated regimes where the ratio of co-flow and counter-flow superfluid stiffnesses can diverge, corresponding to the case of saturated drag.

Dual-species Bose-Einstein condensate of K41 and Rb87 in a hybrid trap

“…Within an experimental cycle of less than 20 s, we produce stable dual-species BECs with more than 10 5 atoms and tunable species population imbalance. This result represents a convenient starting point for future studies on mass-imbalanced superfluid mixtures with tunable interactions which are expected to exhibit exotic phenomena such as the formation of unusual vortex structures [56,57], self-bound states [58] and non-dissipative drag effects [1,[59][60][61][62].…”

Superfluid drag in multicomponent Bose-Einstein condensates on a square optical lattice

“…The winding number W i is a a topological quantity, for a system with periodic spatial boundary conditions, counting the net number of times the particle trajectories wind around the system in direction i. In the multicomponent case, following the derivation of Ref [23], the drag is given by…”

Dissipationless Vector Drag--Superfluid Spin Hall Effect

“…In the condensed matter context, the effect became of great interest with the advent of optical lattices, which allow for a precise control of strongly correlated superfluids [14,15]. The strength of the Andreev-Bashkin drag is controlled by the optical lattice parameters in combination with on-site interactions [16]. It was shown that the effect, in relative terms, can be arbitrarily strong and that the Andreev-Bashkin drag-coefficient ρ ab can also become negative.…”

“…In the latter case, one deals with a counterflow, where the flow of one component generates a mass flow of the other component in the opposite direc-tion [8][9][10][11]. It was pointed out that the effect should lead to formation of new superfluid states where only dissipationless co-flow (paired superfluids) or only counterflow (supercounterfluids) can exist [8][9][10][11][12][13][16][17][18]. At the same time even relatively weak drag substantially changes rotational responses [19,20].…”