Single Quantum Level Electron Turnstile
  We report on the realization of a single-electron source, where current is transported through a single-level quantum dot (Q), tunnel-coupled to two superconducting leads (S). When driven with an ac gate voltage, the experiment demonstrates electron turnstile operation. Compared to the more conventional superconductor - normal metal - superconductor turnstile, our SQS device presents a number of novel properties, including higher immunity to the unavoidable presence of non-equilibrium quasiparticles in superconducting leads. In addition, we demonstrate its ability to deliver electrons with a very narrow energy distribution. 
D. M. T. van Zanten, D. M. Basko, I. M. Khaymovich, J. P. Pekola, H.   Courtois, C. B. Winkelmann
cond-mat.mes-hall