Decay of the Zero-Voltage State in Small-Area, High-Current-Density Josephson Junctions

We have measured the distribution in current for the onset of voltage in small-area Josephson junctions for temperatures down to \ensuremath{\sim}1.6 K. The lifetime of the $〈V〉=0$ state for our highest current density junctions becomes temperature independent for ${k}_{\mathrm{B}}T\ensuremath{\lesssim}\frac{\ensuremath{\hbar}{\ensuremath{\omega}}_{0}}{20}$, a $T$ much less than the WKB prediction (${\ensuremath{\omega}}_{0}$ is the junction resonant frequency). This is consistent with the Caldeira-Leggett theory, which includes damping effects on the quantum tunneling rate.

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