Spectroscopic Evidence of the Aharonov-Casher effect in a Cooper Pair Box

M. T. Bell, W. Zhang, L. B. Ioffe, M. E. Gershenson

Published 2015-04-21Version 1

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. By varying the charge $n_{g}$ induced on the CPB island, we observed oscillations of the device spectrum with the period $\Delta n_{g}=2e$. 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 $n_{g}=e(2n+1)$. The CPB in this regime represents the $4\pi$-periodic Josephson element, which can be used for the development of the parity-protected superconducting qubits.