A coherent hybrid of states with different number of Cooper pairs can be built in a superconductor grain as a result of periodically repeated discrete encounters with bulk superconductor leads. As a direct manifestation of such states a non-dissipative current depending on the phase difference between the leads can be measured.
@article{arxiv.cond-mat/0012201,
title = {Coherent transfer of Cooper pairs by a movable grain},
author = {L. Y. Gorelik and A. Isacsson and Y. M. Galperin and R. I. Shekhter and M. Jonson},
journal= {arXiv preprint arXiv:cond-mat/0012201},
year = {2009}
}