Condensation of an instanton gas

The problem of instanton interactions is considered for the case of dissipative tunneling out of a metastable state. The complex ground-state energy is expressed in terms of the pressure of the interacting instanton gas evaluated at a purely imaginary fugacity. With the Yang-Lee theory it is shown that for sufficiently small barrier height a gas-liquid condensation occurs. As a consequence the decay rate becomes much smaller than the corresponding ideal gas result. This is compared with experiments on tunneling in strongly damped superconducting quantum-interference devices.