Josephson junctions with a phase drop pi in the ground state allow to create vortices of supercurrent carrying only half of the magnetic flux quantum Phi_0~2.07*10^-15 Wb. Such semifluxons have two-fold degenerate ground states denoted up (with flux +Phi_0/2 and supercurrent circulating clockwise) and down (with flux -Phi_0/2 and supercurrent circulating counterclockwise). We investigate a molecule consisting of two coupled semifluxons in a 0-pi-0 long Josephson junction. The fluxes (polarities) of semifluxons are measured by two on-chip SQUIDs. By varying the dc bias current applied to the 0-pi-0 junction, we demonstrate controllable manipulation and switching between two states, up-down and down-up, of a semifluxon molecule. These results provide a major step towards employing semifluxons as bits or qubits for classical and quantum digital electronics.
@article{arxiv.0809.1346,
title = {Semifluxon molecule under control},
author = {Andreas Dewes and Tobias Gaber and Dieter Koelle and Reinhold Kleiner and Edward Goldobin},
journal= {arXiv preprint arXiv:0809.1346},
year = {2008}
}