Josephson tunnel junctions with nonlinear damping for RSFQ-qubit circuit applications

TL;DR

This paper introduces a novel nonlinear damping approach using S-I-N structures to improve Josephson junctions, enhancing their suitability for qubit readout and control by reducing noise and hysteresis.

Contribution

It demonstrates that S-I-N shunting modifies Josephson dynamics, enabling non-hysteretic behavior and low noise, which is beneficial for quantum computing applications.

Findings

S-I-N shunting significantly alters Josephson dynamics.

The junctions exhibit non-hysteretic I-V characteristics at low temperatures.

Reduced damping and noise improve qubit readout and control.

Abstract

We demonstrate that shunting of Superconductor-Insulator-Superconductor Josephson junctions by Superconductor-Insulator-Normal metal (S-I-N) structures having pronounced non-linear I-V characteristics can remarkably modify the Josephson dynamics. In the regime of Josephson generation the phase behaves as an overdamped coordinate, while in the superconducting state the damping and current noise are strikingly small, that is vitally important for application of such junctions for readout and control of Josephson qubits. Superconducting Nb/AlO${_x}$/Nb junction shunted by Nb/AlO${_x}$/AuPd junction of S-I-N type was fabricated and, in agreement with our model, exhibited non-hysteretic I-V characteristics at temperatures down to at least 1.4 K.