  Liquid helium under negative pressure represents a unique possibility for
studying the macroscopic quantum nucleation phenomena in condensed media. We
analyze the quantum cavitation rate of single electron bubbles at low
temperatures down to absolute zero. The energy dissipation and sound emission
processes result in the different temperature behavior of quantum cavitation
rate in normal fluid $^3$He and superfluid $^4$He below the thermal-quantum
crossover temperature. The position of rapid nucleation line in the
temperature-pressure phase diagram is discussed as well.
