Tuning Tunneling Resistance of Josephson Junctions for Precise Qubit Control

Abstract

Superconducting qubits are leading candidates in the race to build a quantum computer that is capable of realizing computations beyond the reach of modern supercomputers. To build scalable systems of superconducting qubits, it is essential to achieve precise control of qubit frequencies to a level not yet reachable by fabrication. The most commonly employed method to set qubit frequency post-fabrication is by using fluxtunable qubits, but adding flux-bias lines could introduce additional noise channels. This report presents progress towards using current to adjust the tunneling resistance of Josephson junctions and tune qubit frequencies. It is observed that under constant DC current, the junctions first show slow increase in resistance, then fast decrease in resistance until reaching complete breakdown, and both processes could be used for tuning. The mechanisms behind the two processes are explored in detail, and the accuracy and practicality of both tuning directions are characterized. Further work will be done improve the tuning accuracy in both directions.