Scale-invariant fluxes are the defining property of turbulent cascades, but their direct measurement is a notorious problem. Here we perform such a measurement for a direct energy cascade in a turbulent quantum gas. Using a time-periodic force, we inject energy at a large lengthscale and generate a cascade in a uniformly-trapped Bose gas. The adjustable trap depth provides a high-momentum cutoff $k_{\textrm{D}}$ , which realises a synthetic dissipation scale. This gives us direct access to the particle flux across a momentum shell of radius $k_{\textrm{D}}$ , and the tunability of $k_{\textrm{D}}$ allows for a clear demonstration of the zeroth law of turbulence. Moreover, our time-resolved measurements give unique access to the pre-steady-state dynamics, when the cascade front propagates in momentum space.Scale-invariant fluxes are the defining property of turbulent cascades, but their direct measurement is a notorious problem. Here we perform such a measurement for a direct energy cascade in a turbulent quantum gas. Using a time-periodic force, we inject energy at a large lengthscale and generate a cascade in a uniformly-trapped Bose gas. The adjustable trap depth provides a high-momentum cutoff $k_{\textrm{D}}$, which realises a synthetic dissipation scale. This gives us direct access to the particle flux across a momentum shell of radius $k_{\textrm{D}}$, and the tunability of $k_{\textrm{D}}$ allows for a clear demonstration of the zeroth law of turbulence. Moreover, our time-resolved measurements give unique access to the pre-steady-state dynamics, when the cascade front propagates in momentum space.

Jan 15, 201918 citations

Synthetic dissipation and cascade fluxes in a turbulent quantum gas

Nir Navon, Christoph Eigen, Jinyi Zhang +6 more

Down and down the energy cascade Injecting energy into a turbulent system at large length scales results in the energy cascading down and eventually dissipating at a characteristic small length scale. In conventional fluids, this small scale is set by fluid viscosity. Navon et al. studied the turbulence energy cascade in a quantum gas, a Bose-Einstein condensate of rubidium-87 atoms held in a uniform trap. Dissipation occurred by atoms escaping from the trap at a scale that could be tuned by varying the height of the trapping potential. Thanks to the flexibility of their setup, the researchers were able to study both the steady state, in which energy is injected at the same rate it is dissipated, and the transient regime preceding the steady state. Science , this issue p. 382Down and down the energy cascade Injecting energy into a turbulent system at large length scales results in the energy cascading down and eventually dissipating at a characteristic small length scale. In conventional fluids, this small scale is set by fluid viscosity. Navon et al. studied the turbulence energy cascade in a quantum gas, a Bose-Einstein condensate of rubidium-87 atoms held in a uniform trap. Dissipation occurred by atoms escaping from the trap at a scale that could be tuned by varying the height of the trapping potential. Thanks to the flexibility of their setup, the researchers were able to study both the steady state, in which energy is injected at the same rate it is dissipated, and the transient regime preceding the steady state. Science , this issue p. 382

arXiv:1807.07564ScienceOct 3, 201982 citations

Turbulence in a quantum gas

Brian P. Anderson

NatureNov 1, 20165 citations

k_{\textrm{D}}

, which realises a synthetic dissipation scale. This gives us direct access to the particle flux across a momentum shell of radius

k_{\textrm{D}}

, and the tunability of

k_{\textrm{D}}

allows for a clear demonstration of the zeroth law of turbulence. Moreover, our time-resolved measurements give unique access to the pre-steady-state dynamics, when the cascade front propagates in momentum space.