2 research outputs found
The size of macroscopic superposition states in flux qubits
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.Comment: 7 pages, no figure
Electronic structure of superposition states in flux qubits
Flux qubits, small superconducting loops interrupted by Josephson junctions,
are successful realizations of quantum coherence for macroscopic variables.
Superconductivity in these loops is carried by --
electrons, which has been interpreted as suggesting that coherent
superpositions of such current states are macroscopic superpositions analogous
to Schr\"odinger's cat. We provide a full microscopic analysis of such qubits,
from which the macroscopic quantum description can be derived. This reveals
that the number of microscopic constituents participating in superposition
states for experimentally accessible flux qubits is surprisingly but not
trivially small. The combination of this relatively small size with large
differences between macroscopic observables in the two branches is seen to
result from the Fermi statistics of the electrons and the large disparity
between the values of superfluid and Fermi velocity in these systems.Comment: Minor cosmetic changes. Published version