Theory of quantum nucleation of bubbles in liquid helium

We calculate the rate at which bubbles form by quantum tunneling in liquid helium-3 and helium-4 at negative pressure. We find that quantum tunneling should be observable at temperatures below about 0.1 K in helium-3 and 0.2 K in helium-4, and at pressures close to the critical negative pressure at which the liquid becomes unstable against long wavelength density fluctuations.