Dephasing due to quasiparticle tunneling in fluxonium qubits: a phenomenological approach

TL;DR

This paper investigates quasiparticle tunneling-induced dephasing in fluxonium qubits, proposing a phenomenological model linking heat currents and temperature gradients to qubit stability, and finds that dephasing time improves with increased inductance.

Contribution

It introduces a phenomenological approach to understand quasiparticle tunneling dephasing in fluxonium qubits, emphasizing heat currents and device parameters affecting coherence.

Findings

Dephasing time is insensitive to the number of junctions in the superinductance.

Dephasing time increases quadratically with the shunt-inductance.

The model links heat currents and temperature gradients to qubit dephasing.

Abstract

The fluxonium qubit has arisen as one of the most promising candidate devices for implementing quantum information in superconducting devices, since it is both insensitive to charge noise (like flux qubits) and insensitive to flux noise (like charge qubits). Here, we investigate the stability of the quantum information to quasiparticle tunneling through a Josephson junction. Microscopically, this dephasing is due to the dependence of the quasiparticle transmission probability on the qubit state. We argue that on a phenomenological level the dephasing mechanism can be understood as originating from heat currents, which are flowing in the device due to possible effective temperature gradients, and their sensitivity to the qubit state. The emerging dephasing time is found to be insensitive to the number of junctions with which the superinductance of the fluxonium qubit is realised. Furthermore, we find that the dephasing time increases quadratically with the shunt-inductance of the circuit which highlights the stability of the device to this dephasing mechanism.