Quantum Cherenkov Transition in Bose Polaron Systems

We study the behavior of a finite-momentum impurity immersed in a weakly interacting Bose-Einstein condensate (BEC) of ultra-cold atoms near an interspecies Feshbach resonance. Using the time-dependent variational approach and a non-Gaussian transformation, we study both ground state properties and quench dynamics of the system after a sudden immersion of the impurity into the BEC. While in the subsonic regime dynamics corresponds to relaxation into the quasiparticle state, in the supersonic regime we observe rapid emission of Cherenkov phonons. This phenomenon manifests in several ways during real-time dynamics of the system and showcases a rich interplay between polaronic physics and Cherenkov physics. We see qualitatively different long-time behavior of average impurity speed and Loschimdt echo depending on the impurity-boson interaction strength. Aspects of the discussed dynamical behavior can be probed in experimental protocols.