3e tunneling processes in a superconducting single-electron tunneling transistor

A current due to a tunneling event that involves three times the charge of an electron was observed in the current - voltage characteristics of a superconducting single-electron tunneling transistor. In this tunnel event, a Cooper pair tunnels through one tunnel barrier simultaneously with a quasiparticle that tunnels through a second tunnel barrier which is about 0.5 microns distant from the first tunnel barrier. This current was observed in a bias regime where current flow due to sequential quasiparticle tunneling is forbidden due to the Coulomb blockade.