Vortex dynamics in superfluids governed by an interacting gauge theory

Abstract

We study the dynamics of a vortex in a quasi two-dimensional Bose gas consisting of light-matter coupled atoms forming two-component pseudo spins. The gas is subject to a density dependent gauge potential, hence governed by an interacting gauge theory, which stems from a collisionally induced detuning between the incident laser frequency and the atomic energy levels. This provides a backaction between the synthetic gauge potential and the matter field. A Lagrangian approach is used to derive an expression for the force acting on a vortex in such a gas. We discuss the similarities between this force and the one predicted by Iordanskii, Lifshitz and Pitaevskii when scattering between a superfluid vortex and the thermal component is taken into account. the preferred environment for investigating turbulence phenomena. The study of the dynamics of quantised vortices represented the first step to this aim. The experimental realisation of BEC of alkali atoms in 1995 [10,11], gave a significant boost in this direction. Because of the unprecedented control and access to physical parameters of the atomic cloud, these systems have provided an excellent experimental environment for studying the dynamics of quantised vortices and their properties in general [12][13][14].Particular attention has been drawn to the problem of Magnus like transverse forces in quantum fluids. These forces, first predicted in classical hydrodynamics, are orthogonal to the relative motion between an object, carrying a flow of circulation, and the fluid in which it is immersed. The forces at play in this situation, and their derivation, has not been without controversy. At the heart of this debate, is the dual nature of a quantum fluid at finite temperature, where it consists of a superfluid and a normal component of thermally excited quasiparticles. According to this two-fluid model, different transverse forces acting on a vortex should in principle be expected. Whereas there is a wide consensus on the existence of a superfluid Magnus force, which can be considered the analogue of the effect predicted by the Kutta-Joukowski theorem for an inviscid classical fluid, the existence of a thermal Magnus force is still the object of some debate. Such forces was theoretically predicted by Lifshitz and Pitaevskii [15] and Iordanskii [16,17], who showed that this type of force is a consequence of the interaction between a vortex and the roton and phonon quasi-particles respectively.Recently Ao and Thouless [18,19] contested the existence of any thermal Magnus force. Deircan et al [20] arrived at the same conclusion analysing the phonon scattering by a vortex using a hydrodynamical approach. These results have been confuted by Sonin [21][22][23], who argued it is incorrect ignoring particular properties of the Born cross-section at small angles, which if included, results in a thermal transverse force. More recently a comprehensive study by Flaig and Fischer [24] also confirms the existence of a transverse force acting on a vortex, where any singularities wer...

Synthetic flux attachment

“…In the following, we extend the treatment of Refs. [35,60,61,65] to include long-range interactions and nonzero detuning.…”

“…More importantly, what are they useful for, and are there any physical systems where these are present? So far, density-dependent gauge fields have been used in the context of pseudolinear "anyons" [48,56,57], as a mechanism to induce frustration on a lattice [58], and in condensates with exotic phenomenology [59][60][61][62][63][64][65][66].…”

Non-integrable dynamics of matter-wave solitons in a density-dependent gauge theory

“…This has led to the realization of vortex states [34] as well as spin-orbit coupling [35]. Interest was recently focused on schemes for generating gauge potentials with an effective back-action between the matter and the gauge potential [36,37], which leads to a number of novel phenomena, including the violation of the Kohn's theorem [38,39], and unconventional vortex dynamics [40,41]. Very recently, the first experimental realization of a dynamical gauge theory in a trapped ion system was shown [42] .…”

On the hydrodynamics of nonlinear gauge-coupled quantum fluids

“…where Ω is the Rabi frequency characterising the lightmatter coupling and φ is the phase of the laser field. By assuming that the N -body wavefunction is a product of N identical single-particle wavefunctions, we obtain [39] a meanfield Lagrangian in the form of equation 1, wherê H M F acts on the two-component macroscopic wavefunction, ψ, aŝ…”