We have measured the current-voltage characteristics of small-capacitance single Josephson junctions at low temperatures (T < 0.04 K), where the strength of the coupling between the single junction and the electromagnetic environment was controlled with one-dimensional arrays of dc SQUIDs. We have clearly observed Coulomb blockade of Cooper-pair tunneling and even a region of negative differential resistance, when the zero-bias resistance of the SQUID arrays is much higher than the quantum resistance h/e^2 = 26 kohm. The negative differential resistance is evidence of coherent single-Cooper-pair tunneling in the single Josephson junction.
@article{arxiv.cond-mat/0103502,
title = {Coulomb Blockade and Coherent Single-Cooper-Pair Tunneling in Single Josephson Junctions},
author = {Michio Watanabe and David B. Haviland},
journal= {arXiv preprint arXiv:cond-mat/0103502},
year = {2009}
}