Abstract
Coherently coupled two-component Bose-Einstein condensates (BEC) exhibit vortex confinement resembling quark confinement in Quantum Chromo Dynamics (QCD). Fractionally quantized vortices winding only in one of two components are attached by solitons, and they cannot stably exist alone. Possible stable states are "hadrons" either of mesonic type, i.e., molecules made of a vortex and anti-vortex in the same component connected by a soliton, or of baryonic type, i.e., molecules made of two vortices winding in two different components connected by a soliton. Mesonic molecules move straight with a constant velocity while baryonic molecules rotate. We numerically simulate collision dynamics of mesonic and baryonic molecules and find that the molecules swap a partner in collisions in general like chemical and nuclear reactions, summarize all collisions as vortex reactions, and describe those by Feynman diagrams. We find a selection rule for final states after collisions of vortex molecules, analogous to that for collisions of hadrons in QCD.
Highlights
Ultracold atomic gases are experimentally controllable systems offering setups to simulate various problems in physics [1,2,3]
They allow vortex molecules, fractionally quantized vortices confined by solitons [8], which are suggested to share several properties with confinement phenomena of quantum chromodynamics (QCD), a theory of the strong interaction consisting of quarks and gluons
In order to further understand the similarities between Bose-Einstein condensates (BEC) and QCD, we focus on the few-body dynamics of vortex molecules, more precisely their collisions, in contrast to previous works focusing on dynamics of either single molecules [14,15,16] or many molecules describing vortex lattices [12] or the Berezinskii-Kosterlitz-Thouless transition [17]
Summary
Ultracold atomic gases are experimentally controllable systems offering setups to simulate various problems in physics [1,2,3]. Coherently coupled two-component BECs realized by the JILA group [6,7] are one interesting system for understanding high-energy physics; when each component is a different hyperfine state of the same atom, one can introduce a Rabi (Josephson) coupling between them They allow vortex molecules, fractionally quantized vortices confined by solitons (linearly extended objects) [8], which are suggested to share several properties with confinement phenomena of quantum chromodynamics (QCD), a theory of the strong interaction consisting of quarks and gluons. There are two possibilities for the soliton to select the vortices in a pair on its two endpoints: Either a vortex and an antivortex in the same component such as u and u (d and d ) or vortices in different species such as u and d (uand d ) We have called the former a mesonic vortex molecule and the latter a baryonic vortex molecule in analogy with QCD.
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