The Sinis Turnstile: towards a Quantum Current Standard

In order to create such a standard, we focus on developing a single-electron turnstile based on two mesoscopic normal metal (N) – insulator (I) – superconductor (S) tunnel junctions [2]. Even though the trade-off between missed tunneling and higher-order tunneling processes limits the current of a single device to around 10 30 pA [3], the device is simple enough to be parallelized, and high enough currents can be reached [4]. However, the lowest attained uncertainty is still limited to 10−4. The most notable known error sources of the SINIS turnstile are higher order tunneling processes, photon assisted tunneling and quasiparticle excitations. From these, the first one can be suppressed to appropriate level by proper geometry and the middle one by proper filtering and shielding, but quasiparticle excitations still remain a problem. As with higher order processes, also the quasiparticle exitations can be minimized with tuning the geometry [5]. However, the requirements of these two are challenging to attain at the same time. At the moment, we are focusing to fabricate 10 parallel samples, where all the known error sources would be minimized.