Rotational quantum friction in superfluids: Radiation from object rotating in superfluid vacuum

The friction experienced by a body rotating in a superfluid liquid at T=0 is discussed. The effect is analogous to the amplification of electromagnetic radiation and spontaneous emission by a body or black hole rotating in the quantum vacuum, first discussed by Zel'dovich and Starobinsky. The friction is caused by the interaction of the part of the liquid which is rigidly connected with the rotating body and thus represents a comoving detector, with the "Minkowski'' superfluid vacuum outside the body. The emission process is the quantum tunneling of quasiparticles from the detector to the ergoregion, where the energy of quasiparticles is negative in the rotating frame. This quantum rotational friction caused by the emission of quasiparticles is estimated for phonons and rotons in superfluid He-4 and for Bogoliubov fermions in superfluid He-3. (C) 1999 American Institute of Physics. [S0021-3640(99)00104-8].