The promise of single Cooper pair quantum circuits based on tunnel junctions for metrology and quantum information applications is severely limited by the influence of "offset" charges - random, slowly drifting microscopic charges inherent to many solid-state systems. By shunting a small junction with the Josephson kinetic inductance of a series array of large capacitance tunnel junctions, thereby ensuring that all superconducting islands are connected to the circuit by at least one large junction, we have realized a new superconducting artificial atom which is totally insensitive to offset charges. Yet, its energy levels manifest the anharmonic structure associated with single Cooper pair effects, a useful component for solid state quantum computation.
@article{arxiv.0906.0831,
title = {Fluxonium: single Cooper pair circuit free of charge offsets},
author = {Vladimir E. Manucharyan and Jens Koch and Leonid Glazman and Michel Devoret},
journal= {arXiv preprint arXiv:0906.0831},
year = {2015}
}