Achieving the Threshold Regime with an Overscreened Josephson Junction

We demonstrate that by utilizing an overscreened Josephson junction as a noise detector it is possible to achieve the threshold regime, whereby the tails of the fluctuating current distribution are measured. This situation is realized by placing the Josephson junction and mesoscopic conductor in an external circuit with very low impedance. In the underdamped limit, overscreening the junction inhibits the energy diffusion in the junction, effectively creating a tunable activation barrier to the dissipative state. As a result, the activation rate is qualitatively different from the Arrhenius form.

Figure 1

The negative logarithm of the escape rate is plotted versus dimensionless barrier height $\Delta U/E_C$ for various values of the threshold parameter $\mathcal{P}$. The solid lines correspond to Poissonian noise, while the dashed line corresponds to a QPC with transparency $\mathcal{T}=0.06$. Inset: Simplified electrical circuit for the Josephson junction (JJ, marked with an $\mathsf{X}$) threshold detector of the noisy mesoscopic system.