QUANTUM FLUCTUATIONS IN FINITE SIZE JOSEPHSON-JUNCTIONS

An effective Josephson coupling energy for a one-dimensional Josephson junction is renormalized due to quantum fluctuations of the phase difference. In a long junction at T --> 0 a Kosterlitz-Thouless phase transition takes place. The state with a logarithmically divergent phase-phase correlation function shows a nontrivial combination of phase disorder on a junction surface with phase order in the bulk. For finite size junctions the renormalized value of the Josephson coupling energy turns out to be strongly suppressed for small Josephson-to-charging energy ratio. The implications of this effect for Bloch oscillations are discussed.