2018/05/31 by Weizhe Edward Liu, Jesper Levinsen, Meera M. Parish · 1 citation
Physics and Astronomy · #cond-mat.quant-gas #quant-ph
paper · pdf · doi:10.1103/physrevlett.122.205301
published as Phys. Rev. Lett. 122, 205301 (2019) · 4 pages of main text with a 5-page supplementary material (SM); 2 figures in the main text and another 3 in the SM
arxiv created 2019/05/21 · arxiv updated 2019/05/29
We present a general variational principle for the dynamics of impurity particles immersed in a quantum-mechanical medium. By working within the Heisenberg picture and constructing approximate time-dependent impurity operators, we can take the medium to be in any mixed state, such as a thermal state. Our variational method is consistent with all conservation laws and, in certain cases, it is equivalent to a finite-temperature Green's function approach. As a demonstration of our method, we consider the dynamics of heavy impurities that have suddenly been introduced into a Fermi gas at finite temperature. Using approximate time-dependent impurity operators involving only one particle-hole excitation of the Fermi sea, we find that we can successfully model the results of recent Ramsey interference experiments on 40K atoms in a 6Li Fermi gas [M.~Cetina et al., Science 354, 96 (2016)]. We also show that our approximation agrees well with the exact solution for the Ramsey response of a fixed impurity at finite temperature. Our approach paves the way for the investigation of impurities with dynamical degrees of freedom in arbitrary quantum-mechanical mediums.