FLUX-MODULATED ANDREEV CURRENT CAUSED BY ELECTRONIC INTERFERENCE

We have performed an interference experiment with two tunnel junctions between a thin normal metal wire and a superconducting fork. We have found that the subgap current is strongly modulated by the flux throug h the resulting normal-superconducting loop. Our results agree with th e recent prediction that multiple tunnel attempts of electron pairs, w hich occur when electrons are confined near the junction, can add cohe rently if the pair consists of nearly time-reversed states.