Josephson Junction Tuning Described by Depinning Physics

Abstract

Superconducting quantum computers leverage superconducting qubits, systems with well-defined energy levels, the spacing of which is determined by the properties of embedded Josephson junctions. Indeterminacy of Josephson junction manufacturing limits large-scale superconducting circuits; however, junction-by-junction tuning affords the possibility of an order of magnitude improvement of determinacy—although the origin of this tuning effect is uncertain. Understanding how tuning techniques may physically modify the tunnel barrier of a Josephson junction is important and will enable these techniques to be optimized. We develop a model of junction tuning based on depinning theory to interpret a phase diagram of the tuning rate. We extract the dependence on temperature, time-varying voltages, and oscillation frequency. Comparing the effect of junction tuning on room-temperature I−V’s, electrical breakdown, and frequency of higher-energy levels of transmon qubits indicates that the tuning process leaves the barrier thickness unchanged but modifies its composition.

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