MAGNETIC-FLUX LOCKING IN 2 WEAKLY COUPLED SUPERCONDUCTING RINGS

We have analyzed the quantum interference effects in the macroscopic ' 'superconducting molecule.'' The composite system consists of two mass ive superconducting rings, each interrupted by a Josephson junction, w hich are at the same time weakly coupled with one another. The special case of coupling via the Josephson four-terminal junction is consider ed. The structure of the macroscopic quantum states in an applied magn etic field is calculated. It is shown that, depending on the values of the magnetic fluxes through each ring, the system displays two groups of states, the ''orthostates'' with both induced currents going in th e same direction, and the ''parastates'' with the opposite currents an d with the total induced flux locked to zero value. The transition to the flux locked state with changing of the total applied flux is sudde n and is preserved in a certain interval which is determined by the di fference of the fluxes applied through each ring. It makes the system sensitive to small gradients of the external magnetic field. (C) 1998 American Institute of Physics. [S1063-777X(98)01410-8]