The achievable fidelity of many nanoelectronic devices based on superconducting aluminum is limited by either the density of residual nonequilibrium quasiparticles n_qp or the density of quasiparticle states in the gap, characterized by Dynes parameter \gamma. We infer upper bounds n_qp < 0.033 um^-3 and \gamma < 1.6*10^-7 from transport measurements performed on Al/AlOx/Cu single-electron transistors, improving previous results by an order of magnitude. Owing to efficient microwave shielding and quasiparticle relaxation, typical number of quasiparticles in the superconducting leads is zero.
@article{arxiv.1106.1326,
title = {Vanishing quasiparticle density in a hybrid Al/Cu/Al single-electron transistor},
author = {O. -P. Saira and A. Kemppinen and V. F. Maisi and J. P. Pekola},
journal= {arXiv preprint arXiv:1106.1326},
year = {2012}
}
Comments
5 pages, 3 figures; updated to revised version that was accepted for publication, contains data from a reference sample without qp traps