SINIS turnstile for quantum current standards

Single electron pumping by a SINIS turnstile is investigated up to 1 GHz in various conditions to realize a quantum current standard. A standard deviation of the pumping current at 100 MHz is about 10^-4 at base temperature of a dilution refrigerator. As expected, the plateau of the pumped current degrades as temperature increases because of the thermal smearing of Fermi energy of a normal metal island. On the other hand, an externally applied magnetic fields dramatically suppresses excess current on the single electron pumping plateau. This originates from the quasiparticle relaxation enhancement due to the penetration of the magnetic vortices into the superconducting leads.