Seminarium Optyczne

I will present our latest experimental results on driven box-trapped two-dimensional Bose gases.We have observed first and second sound in the system, which is the first such observation in aBerezinskii-Kosterlitz-Thouless (BKT) superfluid. Measurement of the two sound speeds allows theextraction of the superfluid density as a function of temperature, which agrees with the expected universaljump of the superfluid phase-space density at the transition point.In the second part of my talk, I will focus on a strongly driven gas in which a direct turbulent cascadeemerges. Starting from the microscopic dynamics of the discrete low-lying quantum states of the system, wehave observed two key phenomena conceptually associated with the development of turbulence – theemergence of statistical isotropy under anisotropic forcing, and the spatio-temporal scaling of themomentum spectrum.