By varying the charge ng induced on the CPB island, we observed oscillations of the device spectrum with the period Δng=2e. These oscillations are attributed to the charge-controlled AC interference between the fluxon tunneling processes in the CPB Josephson junctions. Total suppression of the tunneling (complete destructive interference) has been observed for the charge ng=e(2n+1). The CPB in this regime represents the 4π-periodic Josephson element, which can be used for the development of the parity-protected superconducting qubits.
Spectroscopic Evidence of the Aharonov-Casher effect in a Cooper Pair Box
We have observed the effect of the Aharonov-Casher (AC) interference on the spectrum of a superconducting system containing a symmetric Cooper pair box (CPB) and a large inductance.