We have studied the transition between pure potential flow and turbulent flow around a quartz tuning fork resonator in superfluid ${}^4\mathrm{He}$ at millikelvin temperatures. Turbulent flow is identified by an additional drag force on the fork prongs due to the creation of quantized vortices. When driven at a constant driving force amplitude, the transition to turbulence causes an abrupt decrease in the velocity amplitude of the prongs. For a range of driving forces, continuous switching is observed between the two flow states. We have made a statistical study of the switching characteristics and of the lifetimes of the unstable states. We find a characteristic velocity $v^{☆}$ which separates quasistable turbulent flow at higher velocities and quasistable potential flow at lower velocities. We show that the potential-to-turbulent flow transition is driven by random processes involving remanent vortices pinned to the prongs.

• Received 11 February 2014
• Revised 15 April 2014

DOI:https://doi.org/10.1103/PhysRevB.89.214503

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Published by the American Physical Society