Observation of Resonant Tunneling between Macroscopically Distinct Quantum Levels

Abstract

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 \ensuremath{\mu}A. Near 50 mK, the tunneling rate $\ensuremath{\gamma}({\ensuremath{\Phi}}_{x})$ from the metastable well vs applied flux ${\ensuremath{\Phi}}_{x}$ is found to exhibit a series of local maxima where the levels (spaced by $\ensuremath{\approx}1.9$ K) in the two wells cross. The positions of these maxima agree well with the level crossings calculated using independently determined system parameters.