Turbulence is a multi-scale phenomenon, found in systems ranging from non-linear optics to the dynamics of the early universe. While turbulence escapes a complete microscopic understanding it is commonly associated with cascades, transporting system-specific conserved quantities, across different length scales.
Here, we employ a two-dimensional and homogenous ultracold Bose gas – a system with a high degree of experimental tunability – to study wave turbulence. A time-varying magnetic field gradient is used to excite a longest wavelength phonon mode, which under strong driving forms a direct energy cascade from low wavenumbers to high wavenumbers, where the dissipation scale lies. Using complimentary techniques, the system is probed on all length and time scales providing a view from individual quantum states to the full momentum distribution. We reveal two major theoretical cornerstones of turbulence formation: the establishment of the isotropic direct cascade, characterised by a power law, under anisotropic forcing; and the spatiotemporal scaling of the momentum distribution at times before any energy dissipation.
Rather than simply driving the longest wavelength mode, we are also able to excite shorter wavelength modes lying at intermediate wavenumbers using a Digital Micromirror Device. In this scenario, a dual system of two cascades where energy propagates to higher wavenumbers and particle number to lower wavenumbers is expected.
|Presenter name||Andrey Karailiev|
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