The superconducting fluxonium circuit is an artificial atom with a strongly anharmonic spectrum: when biased at a half flux quantum, the lowest qubit transition is an order of magnitude smaller in frequency than those to higher levels. Similar to conventional atomic systems, such a frequency separation between the computational and noncomputational subspaces allows independent optimizations of the qubit coherence and two-qubit interactions. Here we describe a controlled-Z gate for two fluxoniums connected either capacitively or inductively, with qubit transitions fixed near 500 MHz. The gate is activated by a microwave drive at a resonance involving the second excited state. We estimate intrinsic gate fidelities over 99.9% with gate times below 100 ns.
@article{arxiv.1802.03095,
title = {Microwave-Activated Controlled-Z Gate for Fixed-Frequency Fluxonium Qubits},
author = {Konstantin N. Nesterov and Ivan V. Pechenezhskiy and Chen Wang and Vladimir E. Manucharyan and Maxim G. Vavilov},
journal= {arXiv preprint arXiv:1802.03095},
year = {2018}
}