Abstract

A Cooper pair transistor (CPT) consists of a superconducting island coupled to leads only by tunnel barriers. Ordinarily, quasiparticles moving through the island can only exist above the superconducting gap, but entry of superconducting vortices create a sub-gap density of quasiparticle states on the island, modifying the quasiparticle dynamics. This and other interactions of these two objects, for example trapping of a single quasiparticle in a vortex, allows the dynamics of one to be inferred from measurements of the other. CPTs are being fabricated with a view to monitor the quasiparticle tunnelling rates using radio frequency reflectometry at zero and low vorticity. RF reflectometry enables rapid read-out of the island quasiparticle states and with sufficient bandwidth may even allow time-domain resolution of single quasiparticle tunnelling events. In this talk I will summarise the theory of quasiparticles and vortices on CPTs, explain the RF reflectometry technique and show the current progress towards fabricating suitable devices for this experiment.