Coherence properties of the 0-$\pi$ qubit

TL;DR

This paper analyzes how slight variations in circuit elements and coupling to spurious modes impact the coherence and decoherence properties of the 0-$$ qubit, a superconducting qubit promising enhanced protection.

Contribution

It provides a theoretical study of realistic imperfections in the 0-$$ qubit, including parameter dispersion and spurious mode coupling, and estimates achievable coherence times.

Findings

Parameter variations reduce coherence times.

Coupling to spurious modes introduces additional decoherence channels.

Estimated coherence times depend on specific circuit parameters.

Abstract

Superconducting circuits rank among the most interesting architectures for the implementation of quantum information processing devices. The recently proposed 0-$\pi$ qubit [Brooks et al., Phys. Rev. A ${\bf 87}$, 52306 (2013)] promises increased protection from spontaneous relaxation and dephasing. In practice, this ideal behavior is only realized if the parameter dispersion among nominally identical circuit elements vanishes. In this paper we present a theoretical study of the more realistic scenario of slight variations in circuit elements. We discuss how the coupling to a spurious, low-energy mode affects the coherence properties of the 0-$\pi$ device, investigate the relevant decoherence channels, and present estimates for achievable coherence times in multiple parameter regimes.