The size of macroscopic superposition states in flux qubits

¹  Department of Physics and Berkeley Quantum Information and Computation Center, University of California - Berkeley, CA 94720, USA
²  Department of Chemistry and Berkeley Quantum Information and Computation Center, University of California - Berkeley, CA 94720, USA
³  Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo 200 University Avenue West, Waterloo, ON, Canada, N2L 3G1

Corresponding author: whaley@berkeley.edu

Received: 5 December 2009
Accepted: 21 January 2010

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.