Seminarium Optyczne

A mobile impurity immersed into a degenerate Fermi gas is a paradigmatic problem in many-bodyphysics. Dressing of the quantum impurity by a cloud of particle-hole excitations of the environment leadsto formation of quasi-particles which are called polarons. The observations of these quasi-particles inexperiments with ultracold atomic gases or with two-dimensional monolayer semiconductors renewedinterest in the field of quantum impurities. The description of polaron physics in these systems was based onequilibrium theory or wave function techniques. However, a non-equilibrium treatment is needed whichwould include not only coherent quantum processes of quasi-particle formation but also time-dependentexternal drive or even pump and loss.In the talk I will describe our approach to non-equilibrium Fermi polaron physics. Based on non-equilibrium quantum field theory, we derived a kinetic equation that includes processes of polaron formationand external fields, and it allows for studying relaxation of polarons and their non-equilibrium distributions.In particular, in the context of ultracold atomic gases, we apply our theory of driven polarons to recentexperiments with ultracold atoms, where Rabi oscillations between a Fermi-polaron state and a non-interacting level were reported. We find a good quantitative agreement between our predictions and theavailable experimental data without any fitting parameter