Group Seminar at MPQ: Dynamics of a driven homogeneous Bose gas from first and second sound to wave turbulence
Timon Hilker, Cambridge
Herbert-Walther lecture hall
Monday, March 2nd, 10:00am
Homogeneous quantum gases are an ideal platform to investigate out-of-equilibrium processes in real time. We continuously drive the lowest spatial mode of a box-trapped Bose gas and study the response of system ranging from density waves in linear response, via purely non-linear damping of the fundamental mode, to the turbulent cascades for strong drive. At finite temperatures, we reach sufficiently hydrodynamic conditions to observe both first and second sound confirming the weakly interacting limit of Landau's two-fluid model. For stronger sound waves, higher modes of the gas are excited via collisions leading to non-linear damping and 3rd-harmonics generation. This can be seen as the onset of a cascade front propagating to higher and higher momenta up to the energy of the trap depth, where particles are lost. We measure the resulting quasi-stationary turbulent state, which is characterized by a power-law distribution in k-space connecting the long wavelength of the drive to the microscopic scale of the dissipation via a constant particle and energy flux.