Dynamics of finite momentum Bose polarons
Name
1124958155-MIT.pdf
Size
4.17 MB
Format
Adobe PDF
Checksum (MD5)
602e750c9e6d4e8427cc1d2e24cb7da8
Author(s)
Seetharam, Kushal.
Advisor(s)
Eugene Demler.
Date Issued
2019
Publisher
Massachusetts Institute of Technology
Abstract
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, we study both ground state properties and quench dynamics of the system after a sudden immersion of the impurity into the BEC. We find evidence of a ground state phase transition when the impurity has a velocity greater than that of the sound velocity (Landau critical velocity) associated with Bogoliubov quasiparticle excitations of the BEC. As we cross from the subsonic regime to the supersonic regime, we get a breakdown of the polaron quasiparticle description of the system, emission of Cherenkov phonons, and a sound-like dispersion of the system. This phase transition manifests in several ways during real-time dynamics of the system and showcases a rich interplay between polaronic physics and Cherenkov physics. One key signature, dissipation in the the supersonic regime, can be seen in experimental protocols where the impurity and BEC are made to move relative to each other through an external force. We suggest one such experimental protocol to measure the polaron's effective mass as long as the impurities are subsonic. While the measurement scheme becomes error-prone due to dissipation when the impurities are allowed to become supersonic, this sensitivity suggests a way to experimentally probe the Cherenkov physics of supersonic impurities immersed in a BEC.
Description
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2019
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 30-31).
Subjects
Electrical Engineering and Computer Science.
MIT Department
Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science
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