Influence of a mesoscopic bath on quantum coherence

Abstract

For a quantum double well system interacting with a mesoscopic bath, it is shown that a ``bath'' consisting of a single particle is sufficient to substantially reduce tunneling between the two wells. This is demonstrated by considering an ammonia molecule in the center of a ring; in addition to halving the maser line frequency, there is an increase in intensity by four orders of magnitude. The tunneling varies nonmonotonically with the number $N$ of electrons in the ring, reflecting the changing electronic correlations. Although the tunneling is reduced for small $N$, it turns around and grows to its free value for large $N$. This is shown to not violate Anderson's orthogonality theorem. Experimental implementations are discussed.