The quasicharge superconducting qubit realizes the dual of the transmon and shows strong robustness to flux and charge fluctuations thanks to a very large inductance closed on a Josephson junction. At the same time, a weak anharmonicity of the spectrum is inherited from the parent transmon, that introduces leakage errors and is prone to frequency crowding in multi-qubit setups. We propose a novel design that employs a quartic superinductor and confers a good degree of anharmonicity to the spectrum. The quartic regime is achieved through a properly designed chain of Josephson junction loops that shows minimal quantum fluctuations without introducing a severe dependence on the external fluxes.
@article{arxiv.2304.10401,
title = {The quartic Blochnium: an anharmonic quasicharge superconducting qubit},
author = {Luca Chirolli and Matteo Carrega and Francesco Giazotto},
journal= {arXiv preprint arXiv:2304.10401},
year = {2023}
}