Nonadiabatic charge pumping in a hybrid single-electron transistor

We study theoretically current quantization in the charge turnstile based on the superconductor-normal-metal single-electron transistor. The quantization accuracy is limited by either Andreev reflection or by Cooper-pair-electron cotunneling. The rates of these processes are calculated in the above-the-threshold'' regime when they compete directly with the lowest-order tunneling. By shaping the ac gate voltage drive it should be possible to achieve the metrological accuracy of 10(-8), while maintaining the quantized current on the level of 30 pA, just by one turnstile with realistic parameters using aluminum as a superconductor.