  We investigate quasiparticle tunneling in a Cooper-pair box which is embedded
in a superconducting ring to allow control of the total phase difference across
the island. The phase affects the transition rate between different electron
number parity states of the island, which can be observed in experiment by
established means. The phase dependence also leads to what is known as the
cos-phi term in the tunneling characteristics of classical Josephson junctions.
This effect has remained controversial for decades; the proposed scheme opens
an independent way to probe it.
