Quasiparticle relaxation of superconducting qubits in the presence of flux

TL;DR

This paper develops a flux-dependent theory of quasiparticle tunneling in superconducting qubits, providing estimates for decay rates and a new method to measure junction admittance, crucial for improving qubit coherence.

Contribution

It introduces a general flux-dependent decay rate model for quasiparticles in superconducting qubits, applicable to various quasiparticle distributions and useful for quantum circuit optimization.

Findings

Decay rate depends on magnetic flux and quasiparticle distribution.

Provides estimates for decay rates in practical quantum circuits.

Suggests a new method to measure phase-dependent admittance of Josephson junctions.

Abstract

Quasiparticle tunneling across a Josephson junction sets a limit for the lifetime of a superconducting qubit state. We develop a general theory of the corresponding decay rate in a qubit controlled by a magnetic flux. The flux affects quasiparticles tunneling amplitudes, thus making the decay rate flux-dependent. The theory is applicable for an arbitrary quasiparticle distribution. It provides estimates for the rates in practically important quantum circuits and also offers a new way of measuring the phase-dependent admittance of a Josephson junction.