Superfluids in a Stir

Charles Day

Charles Day

Matthew J. Davis, Kristian Helmerson

R. Citro, Anna Minguzzi, F. W. J. Hekking

We propose quantum stirring with a laser beam as a probe of superfluid behavior for a strongly interacting one-dimensional Bose gas confined to a ring. Within the Luttinger liquid theory framework, we calculate the fraction of stirred particles per period as a function of the stirring velocity, the interaction strength and the coupling between the stirring beam and the bosons. The fraction of stirred particles allows to probe superfluidity of the system. We find that it crosses over at a critical velocity, lower than the sound one, from a characteristic power law at high velocities to a constant at low velocities. Some experimental issues on quantum stirring in ring-trapped condensates are discussed.

R. Citro, Anna Minguzzi, F. W. J. Hekking

We propose quantum stirring with a laser beam as a probe of superfluidlike behavior for a strongly interacting one-dimensional Bose gas confined to a ring. Within the Luttinger liquid theory framework, we calculate the fraction of stirred particles per period as a function of the stirring velocity, the interaction strength, and the coupling between the stirring beam and the bosons. We show that the stirred fraction is never zero due to the presence of strong quantum fluctuations in one dimension, implying imperfect superfluid behavior under transport. Some experimental issues on quantum stirring in ring-trapped condensates are discussed.

Angela White, Nick P. Proukakis, Carlo F. Barenghi

We stir vortices into a trapped quasi two-dimensional atomic Bose-Einstein condensate by moving three laser stirrers. We apply stirring protocols introduced by Boyland et al. (2000), that efficiently build in topological chaos in classical fluids and are classified as Pseudo-Anosov stirring protocols. These are compared to their inefficient mixing counterparts, finite-order stirring protocols. We investigate if inefficient stirring protocols result in a more clustered distribution of vortices. The efficiency with which vortices are 'mixed' or distributed in a condensate is important for investigating dynamics of continuously forced quantum turbulence and the existence of the inverse cascade in turbulent two-dimensional superfluids.