Time-Resolved Measurement of Dissipation-Induced Decoherence in a Josephson Junction

We determined the dissipation-induced decoherence time (DIDT) of a super-conducting Josephson tunnel junction by time-resolved measurements of its escape dynamics. Double-exponential behavior of the time-dependent escape probability was observed, suggesting the occurrence of a two-level decay-tunneling process in which energy relaxation from the excited to the ground level significantly affects the escape dynamics of the system. The observation of temporal double-exponential dependence enables direct measurements of the DIDT, a property critical to the study of quantum dynamics and the realization of macroscopic quantum coherence and quantum computing. We found that the DIDT was$\tau_d > 11\>\mu_s$at T = 0.55 K, demonstrating good prospects for implementing quantum computing with Josephson devices.