Decoherence in Josephson Qubits from Junction Resonances

TL;DR

This paper identifies spurious microwave resonators caused by two-level states in junction barriers as a key decoherence source in Josephson qubits, suggesting material improvements to enhance coherence.

Contribution

It demonstrates the impact of junction barrier two-level states on qubit coherence and highlights the importance of materials research to mitigate these resonances.

Findings

Rabi oscillations observed in an improved phase qubit

Resonators degrade coherence amplitude

Resonators originate from critical current fluctuations

Abstract

Although Josephson junction qubits show great promise for quantum computing, the origin of dominant decoherence mechanisms remains unknown. We report Rabi oscillations for an improved phase qubit, and show that their coherence amplitude is significantly degraded by spurious microwave resonators. These resonators arise from changes in the junction critical current produced by two-level states in the tunnel barrier. The discovery of these high frequency resonators impacts the future of all Josephson qubits as well as existing Josephson technologies. We predict that removing or reducing these resonators through materials research will improve the coherence of all Josephson qubits.