  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.
