Linear Response of a Periodically Driven Thermal Dipolar Gas

We study the nonequilibrium dynamics of an ultracold, non-degenerate dipolar gas of ${}^{164}$Dy atoms in a cylindrically symmetric harmonic trap. To do so, we investigate the normal modes and linear response of the gas when driven by means of periodic modulations to the trap axial-frequency. We find that the resonant response of the gas depends strongly on the dipole alignment axis, owing to anisotropies in the differential cross section of the atoms. We employ the use of the method of averages as well as numerical Monte Carlo methods for our analysis. A striking result is that certain normal modes, termed “melting modes”, initiated in an anisotropic out-of-equilibrium configuration, relax to equilibrium without oscillating.