Time: 1pm AEST - Melbourne, Sydney, Canberra, Brisbane; 3pm NZST

Speaker: Dr Jia Wang
Affiliation: Swinburne University of Technology


We investigate the system of a heavy impurity embedded in a paired two-component Fermi gas at the crossover from a Bose-Einstein condensate (BEC) to a Bardeen-Cooper-Schrieffer (BCS) superfluid. We describe the Fermi superfluid through the conventional Bardeen-Cooper-Schrieffer (BCS) theory and investigate the role of the pairing gap. We calculate the system's Ramsey response and radio-frequency spectroscopy by extending the functional determinant approach (FDA), an in-principal exact numerical approach. 
In a non-interacting ideal Fermi gas, a mobile impurity typically couples with a few particle-hole pairs and forms a celebrated quasiparticle: a polaron. In contrast, an infinitely heavy (or static) impurity can excite many particle-hole pairs close to the Fermi surfaces without costing recoil energy, leading to the occurrence of the well-known phenomenon: Anderson's orthogonality catastrophe (OC). OC means that the many-particle states with and without impurity become orthogonal, giving vanishing quasiparticle residues. 
In a BCS superfluid, the pairing gap plays the same role as recoiling energy to suppress the excitation of multiple particle-hole pairs and prevent the OC. Consequently, using FDA, we can rigorously confirm the remarkable features such as dark continuum, molecule-hole continuum, and repulsive polaron. In addition, for a magnetic impurity scattering at finite temperature, we predict additional resonances related to the subgap Yu-Shiba-Rusinov bound state, whose positions can be used to measure the superfluid pairing gap. We surprisingly find undamped repulsive polarons for a nonmagnetic scattering at zero temperature. These exact results might be readily observed in quantum gas experiments with mixtures of two different species of atoms that have a large-mass ratio.

About Australia - New Zealand Cold Atom Seminars

This new initiative hosts a seminar once a month for the Australia – New Zealand cold atom research community.  The purpose is to encourage and facilitate ongoing discussions and collaboration in the local community.  Talks should be less than 40 minutes in length to allow ample time for questions and discussion.

Seminars will be held on the last Friday of the month (except for December) at 1pm Melbourne time (which is normally 3pm New Zealand time).  While the primary format is online via Zoom, various institutions will host the seminar in local seminar rooms.  The Zoom link is https://uqz.zoom.us/j/88604569495

You can sign up for announcements for the seminars at this webpage:

Seminars are recorded, and past seminars can be accessed from this web page.

Contact Matthew Davis mdavis@physics.uq.edu.au for further information.



Physics Annexe (06)
407 (or via Zoom https://uqz.zoom.us/j/88604569495)