Influence of Dissipation on Quantum Coherence

A quantum mechanical particle which moves in a symmetric double-well potential, and whose interaction with the environment is described in the classical regime by a phenomenological friction coefficient η, is considered. It is shown that, provided ηq₀² exceeds a critical value of order unity (±q₀ are the locations of the potential minima), the mean rate of tunneling between the degenerate minima decreases with temperature, leading at $T=0$ to spontaneous symmetry breaking.