QUANTUM INTERFERENCE OF VORTICES IN JOSEPHSON-JUNCTION ARRAYS

We have experimentally studied a specially shaped array in which vorti ces can cross along a doubly connected path. After vortices are induce d by a magnetic field, we observe a resistive branch in the current-vo ltage characteristic due to these vortex crossings. When the charge th at is enclosed by the path is varied, the flux-flow resistance shows s trong periodic oscillations. These oscillations have been predicted to arise from quantum interference of vortices. The oscilation is period ic with the single electron charge e, instead of the predicted 2e, due to tunneling of quasiparticles.