We present a planar qubit design based on a superconducting circuit that we call concentric transmon. While employing a straightforward fabrication process using Al evaporation and lift-off lithography, we observe qubit lifetimes and coherence times in the order of 10us. We systematically characterize loss channels such as incoherent dielectric loss, Purcell decay and radiative losses. The implementation of a gradiometric SQUID loop allows for a fast tuning of the qubit transition frequency and therefore for full tomographic control of the quantum circuit. Due to the large loop size, the presented qubit architecture features a strongly increased magnetic dipole moment as compared to conventional transmon designs. This renders the concentric transmon a promising candidate to establish a site-selective passive direct Z coupling between neighboring qubits, being a pending quest in the field of quantum simulation.
@article{arxiv.1509.08014,
title = {Concentric transmon qubit featuring fast tunability and an anisotropic magnetic dipole moment},
author = {Jochen Braumüller and Martin Sandberg and Michael R. Vissers and Andre Schneider and Steffen Schlör and Lukas Grünhaupt and Hannes Rotzinger and Michael Marthaler and Alexander Lukashenko and Amadeus Dieter and Alexey V. Ustinov and Martin Weides and David P. Pappas},
journal= {arXiv preprint arXiv:1509.08014},
year = {2018}
}