Decoherence in a superconducting flux qubit with a pi-junction

TL;DR

This paper investigates how pi-junctions can be used in superconducting flux qubits to achieve degenerate quantum states without external magnetic fields, analyzing decoherence effects and estimating coherence times based on experimental parameters.

Contribution

It introduces an effective spin-Boson model for pi-junction flux qubits and assesses conditions for long coherence times, advancing understanding of decoherence in these systems.

Findings

High critical current and large subgap resistance are necessary for long coherence times.

Decoherence is analyzed using the Caldeira-Leggett model.

Estimated dephasing times depend on junction parameters.

Abstract

We consider the use of a pi-junction for flux qubits to realize degenerate quantum levels without external magnetic field. On the basis of the Caldeira-Leggett model, we derive an effective spin-Boson model, and study decoherece of this type of qubits. We estimate the dephasing time by using parameters from recent experiments of SIFS junctions, and show that high critical current and large subgap resistance are required for the pi-junction to realize a long coherent time.