Direct Transition from Quantum Escape to a Phase Diffusion Regime in YBaCuO Biepitaxial Josephson Junctions

Abstract

Dissipation encodes the interaction of a quantum system with the environment and regulates the activation regimes of a Brownian particle. We have engineered grain boundary biepitaxial YBaCuO junctions to drive a direct transition from a quantum activated running state to a phase diffusion regime. The crossover to the quantum regime is tuned by the magnetic field and dissipation is described by a fully consistent set of junction parameters. To unravel phase dynamics in moderately damped systems is of general interest for advances in the comprehension of retrapping phenomena and in view of quantum hybrid technology.

Breakdown of the escape dynamics in Josephson junctions

“…The rate of decrease of σ above T * * turns to be a distinctive marker of the phase dynamics. In device C the slope of σ (T ) above T * * is much smaller when compared to those of JCTs A [40] and B and of all moderately damped JJs. The smooth decrease of σ for T > T * * cannot be described in terms of the intermediate dissipation regime, as evident from the numerical simulations reported in Fig.…”

“…In the MD regime the SCDs become narrower with increasing temperature for temperatures above T * , which is defined as the temperature at which σ (T ) is largest (in the case of JCT B, T * is about 1.0 K). This is often reported in the literature as the phase diffusion (PD) regime [18,[36][37][38]40], indicating a phase diffusive dynamics due to multiple escape and retrapping events in the washboard potential [sketched in Fig. 2(b)], or equivalently described in terms of thermal activation above a dissipation barrier [39].…”

“…The choice of the substrate affects the effective capacitance of the circuit the junction is embedded into [41]. As a consequence of this choice, for JCT B we observed the transition from TA to the PD regime, while for JCT A the TA regime is completely suppressed and we observed a direct transition from MQT to the PD regime [40]. We show below that the anomalous thermal behavior of high J c JCT C cannot be explained in terms of frequency-dependent damping or as a consequence of the shell circuit, and the numerical simulations of Fig.…”

“…Low values of I c [18,[36][37][38][39], especially in HTS d-wave junctions, where intrinsic sources contribute to dissipation [25,40], lead to the moderately damped (MD) regime (Q 1). In the MD regime the SCDs become narrower with increasing temperature for temperatures above T * , which is defined as the temperature at which σ (T ) is largest (in the case of JCT B, T * is about 1.0 K).…”

“…Below T * , SCDs obey the thermal activation (TA) regime. Upon further lowering the temperature the junction can eventually enter the macroscopic quantum tunneling regime [19][20][21]23,40] [see Fig. 1(b), JCT A].…”