Figure (a)
A schematic of the SQUID device used in the Stony Brook and Delft
experiments. Depending on the direction of the magnetic flux through the
superconducting ring, which is about 5 microns across, a persistent current of
about 1 microamp will flow around the device in either the clockwise or
anticlockwise direction (black arrows). The Josephson junction, which is
essential for a superposition to develop, is formed by placing a thin barrier
layer (shown in red), normally an insulating metal oxide, between two
superconducting regions.