The size of macroscopic superposition states in flux qubits

TL;DR

This paper analyzes flux qubits to determine the size of their macroscopic superposition states, revealing that the number of electrons involved is surprisingly small despite large observable differences.

Contribution

It provides a microscopic analysis of flux qubit superpositions, quantifying the actual number of electrons involved in these macroscopic states.

Findings

Number of electrons in superpositions is surprisingly small.

Differences in macroscopic observables are large.

Superpositions are at least mesoscopic.

Abstract

The question as to whether or not quantum mechanics is applicable to the macroscopic scale has motivated efforts to generate superposition states of macroscopic numbers of particles and to determine their effective size. Superpositions of circulating current states in flux qubits constitute candidate states that have been argued to be at least mesoscopic. We present a microscopic analysis that reveals the number of electrons participating in these superpositions to be surprisingly but not trivially small, even though differences in macroscopic observables are large.