Concentric transmon qubit featuring fast tunability and an anisotropic magnetic dipole moment. (arXiv:1509.08014v4 [quant-ph] UPDATED)

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

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