Vanishing quasiparticle density in a hybrid Al/Cu/Al single-electron transistor

摘要

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 γ . We infer upper bounds n _(qp) < 0.033 μm~(-3) and γ < 1.6 × 10~(-7) from transport measurements performed on Al/Cu/Al single-electron transistors, improving previous results by an order of magnitude. Owing to efficient microwave shielding and quasiparticle relaxation, a typical number of quasiparticles in the superconducting leads is zero.