  We discuss the friction experienced by the body rotating in superfluid liquid
at T=0. The effect is analogous to the amplification of electromagnetic
radiation and spontaneous emission by the body or black hole rotating in
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 the comoving detector, with the
"Minkowski" 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 4He and for Bogoliubov fermions in superfluid
3He.
