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.