OBSERVATION OF RESONANT-TUNNELING BETWEEN MACROSCOPICALLY DISTINCT QUANTUM LEVELS

We report the first observation of resonant tunneling of a system between two macroscopically distinct states: energy levels in different fluxoid wells of a weakly damped superconducting quantum interference device which differ in mean current by approximately 6 mu A. Near 50 mK, the tunneling rate Gamma(Phi(x)) from the metastable well vs applied flux Phi(x) is found to exhibit a series of local maxima where the levels (spaced by approximate to 1.9 K) in the two wells cross. The positions of these maxima agree well with the level crossings calculated using independently determined system parameters.