| Abstract: |
| Since that pioneering time, the use of electromechanical probes to test the quantum features of superfluidity has been the workhorse of ultra--low--temperature research. Superfluids exert forces on objects through added mass, normal--fluid drag, mutual friction with vortices, and emission of excitations (phonons and rotons). Electromechanical resonators such as torsional oscillators, vibrating wires, quartz tuning forks, and other microelectromechanical devices (MEMS), because of changes in frequency, damping, and electrical response, provide very sensitive signatures of superfluid flow, quasiparticles, and broken symmetries. However, most of these probes suffer from boundary effects, as they must be attached to the walls of experimental cells. Moreover, the type of motion they allow one to explore is limited mainly to oscillatory motion. Thus, the search began for a dynamical, non--contact electromechanical probe that would allow one to separate intrinsic mechanical losses from fluid--induced ones. These requirements naturally lead to levitation. A levitated object has no mechanical suspension, so there are no clamping losses. However, controlling the dynamics of a levitated object poses additional challenges that we will analyse. |
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