Spontaneous Symmetry Breaking and Decoherence in Superconductors

TL;DR

This paper explores the presence of a thin spectrum in superconductors linked to spontaneous symmetry breaking, affecting coherence times in superconducting qubits and relating to fundamental phenomena like the Meissner and Josephson effects.

Contribution

It demonstrates the existence of a thin spectrum in superconductors consistent with Elitzur's theorem and connects this to coherence times in mesoscopic superconducting qubits.

Findings

Superconductors have a thin spectrum associated with global phase symmetry breaking.

The thin spectrum limits coherence times in superconducting qubits proportional to the number of Cooper pairs.

The work relates symmetry breaking to fundamental effects like the Meissner and Josephson phenomena.

Abstract

We show that superconductors have a thin spectrum associated with spontaneous symmetry breaking similar to that of antiferromagnets, while still being in full agreement with Elitzur's theorem, which forbids the spontaneous breaking of local (gauge) symmetries. This thin spectrum in the superconductors consists of in-gap states that are associated with the spontaneous breaking of a global phase symmetry. In qubits based on mesoscopic superconducting devices, the presence of the thin spectrum implies a maximum coherence time which is proportional to the number of Cooper pairs in the device. Here we present the detailed calculations leading up to these results and discuss the relation between spontaneous symmetry breaking in superconductors and the Meissner effect, the Anderson-Higgs mechanism and the Josephson effect. Whereas for the Meissner effect a symmetry breaking of the phase of the superconductor is not required, it is essential for the Josephson effect.