Spectral function of the Fermi polaron with auxiliary-field Monte Carlo

The Fermi polaron is a paradigmatic system that describes a mobile impurity interacting with a spin-polarized medium. This system has been realized experimentally in spin-imbalanced ultracold Fermi gases. The Fermi polaron problem is of particular interest due to the host of quasiparticle excitations: the attractive polaron, a molecular dimer, and the repulsive polaron. In order to probe these excitations, we use the auxiliary-field quantum Monte Carlo method in the canonical ensemble on a discrete lattice to calculate the imaginary-time Green's function for the polaron problem. The determination of the spectral function from the imaginary-time Green's function is an ill-defined inverse problem that requires a numerical analytic continuation and is carried out by the maximum-entropy method. Our studies are focused on the strongly correlated regime between unitarity and the polaron-dimer transition. We show results for the spectral function at finite lattice filling factor and discuss signatures of the quasiparticle excitations. We also show preliminary results in the continuum limit.