  We present a microscopic open quantum systems theory of thermally-damped
vortex motion in oblate atomic superfluids that includes previously neglected
energy-damping interactions between superfluid and thermal atoms. This
mechanism couples strongly to vortex core motion and causes dissipation of
vortex energy due to mutual friction, as well as Brownian motion of vortices
due to thermal fluctuations. We derive an analytic expression for the
dimensionless mutual friction coefficient that gives excellent quantitative
agreement with experimentally measured values, without any fitted parameters.
Our work closes an existing two orders of magnitude gap between dissipation
theory and experiments, previously bridged by fitted parameters, and provides a
microscopic origin for the mutual friction and diffusion of quantized vortices
in two-dimensional atomic superfluids.
