Quantized current of a hybrid single-electron transistor with   superconducting leads and a normal-metal island
  We discuss the operation of the superconductor - insulator - normal-metal - insulator - superconductor (SINIS) turnstile. This voltage-biased hybrid single-electron transistor (SET) provides current quantization even with only one radio-frequency (rf) control parameter, namely the gate voltage of the single island. We give an overview of the main error mechanisms of the turnstile and consider its feasibility as a quantum current standard. We also present experimental results of pumping with the SINIS structure which show decreased leakage current compared to earlier measurements with the opposite NISIN structure. 
Antti Kemppinen, Matthias Meschke, Mikko M\"ott\"onen, Dmitri V.   Averin and Jukka P. Pekola