We have studied the low-energy excitations in a minimalistic protected Josephson circuit which contains two basic elements (rhombi) characterized by the π periodicity of the Josephson energy. Novel design of these elements, which reduces their sensitivity to the offset charge fluctuations, has been employed. We have observed that the life time T1 of the first excited state of this quantum circuit in the protected regime is increased up to 70μs, a factor of ∼100 longer than that in the unprotected state. The quality factor ω01T1 of this qubit exceeds 106 . Our results are in agreement with theoretical expectations; they demonstrate the feasibility of symmetry protection in the rhombi-based qubits fabricated with existing technology.
Cite
@article{arxiv.1311.6521,
title = {Protected Josephson Rhombi Chains},
author = {Matthew T. Bell and Joshua Paramanandam and Lev B. Ioffe and Michael E. Gershenson},
journal= {arXiv preprint arXiv:1311.6521},
year = {2016}
}