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

TL;DR

This study provides spectroscopic evidence of the Aharonov-Casher effect in a superconducting Cooper pair box, demonstrating charge-controlled interference patterns and potential for parity-protected qubits.

Contribution

First experimental observation of Aharonov-Casher interference in a Cooper pair box with implications for quantum computing.

Findings

Oscillations in device spectrum with period 2e as charge varies

Complete suppression of tunneling at specific charge values

Identification of 4π-periodic Josephson behavior

Abstract

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.