Quantum impurities: from mobile Josephson junctions to depletons

Abstract

We overview the main features of mobile impurities moving in one-dimensional superfluid backgrounds by modeling it as a mobile Josephson junction, which leads naturally to the periodic dispersion of the impurity. The dissipation processes, such as radiative friction and quantum viscosity, are shown to result from the interaction of the collective phase difference with the background phonons. We develop a more realistic depleton model of an impurity-hole bound state that provides a number of exact results interpolating between the semiclassical weakly interacting picture and the strongly interacting Tonks-Girardeau regime. We also discuss the physics of a trapped impurity, relevant to current experiments with ultra cold atoms. Recently the field has received growing attention due to advances in cold atom experiments. Through a number of techniques it became possible to place various impurity atoms in Bose-Einstein condensates (BEC) of alkali atoms, manipulate their mutual scattering strength and apply forces selectively to the impurity atoms. The Cambridge group [15] has used microwave pulses to flip the hyperfine state of a few spatially localized atoms in the BEC of magnetically levitated 87 Rb, turning them into mobile impurities. The impurities, created in the hyperfine m F =0 state, were then accelerated through the BEC by the gravitational force, not compensated by

Many-body quantum dynamics and induced correlations of Bose polarons

“…However, the non-equilibrium dynamics of impurities is far less explored and is expected to be dominated by correlation effects which build up in the course of the evolution [34-36, 39, 42-45]. Existing examples include the observation of self-trapping phenomena [46,47], formation of dark-bright solitons [6,42], impurity transport in optical lattices [48][49][50][51], orthogonality catastrophe events [35,52], injection of a moving impurity into a gas of Tonks-Girardeau bosons [53][54][55][56][57][58][59][60] and the relaxation dynamics of impurities [45,61,62]. Besides these investigations, which have enabled a basic description of the quasiparticle states in different interaction regimes, a number of important questions remain open and a full theoretical understanding of the dynamics specifically of Bose polarons is still far from complete.…”

Dissipative correlated dynamics of a moving impurity immersed in a Bose–Einstein condensate

“…While the majority of these investigations have been mainly focused on the equilibrium properties of the emergent quasiparticles, the dynamics of impurities is far less explored. In this context notable examples include the observation of self-trapping phenomena [46,47], orthogonality catastrophe events [24], generation of dark-bright solitons [15,26], transport properties of impurities in optical lattices [48,49] as well as collisional aspects [50][51][52] of an impurity injected into a gas of Tonks-Girardeau bosons [53][54][55][56][57][58][59][60].…”

Interaction-induced Bloch oscillation in a harmonically trapped and fermionized quantum gas in one dimension

“…In Ref. [8] and earlier theories [9][10][11], this phenomenon was attributed to the Bragg scattering with bosons at the edge of an emergent Brillouin zone, which causes the impurity momentum to change by twice the Fermi momentum of bosons with no energy cost.…”