Environmentally Activated Tunneling Events in a Hybrid Single-Electron Box

TL;DR

This study investigates how external electromagnetic environments influence tunneling events in hybrid single-electron boxes, revealing environmental activation effects, saturation of tunneling rates at low temperatures, and implications for device performance and accuracy.

Contribution

It demonstrates the impact of dissipative electromagnetic environments on tunneling behavior and shows how capacitive shunting can suppress unwanted tunneling rates, advancing understanding of device limitations.

Findings

Anomalous Coulomb step broadening with decreasing temperature.

Saturation of tunneling rates at low temperatures.

Capacitive shunt reduces tunneling rate saturation by over an order of magnitude.

Abstract

We have measured individual tunneling events and Coulomb step shapes in single-electron boxes with opaque superconductor-normal metal tunnel junctions. We observe anomalous broadening of the Coulomb step with decreasing temperature in a manner that is consistent with activation of first-order tunneling events by an external dissipative electromagnetic environment. We demonstrate that the rates for energetically unfavourable tunneling events saturate to finite values at low temperatures, and that the saturation level can be suppressed by more than an order of magnitude by a capacitive shunt near the device. The findings are important in assessing the performance limits of any single-electronic device. In particular, master equation based simulations show that the electromagnetic environment realized in the capacitively shunted devices allows for a metrologically accurate charge pump based on hybrid tunnnel junctions.