Two Qubit Cross Resonance Gate in Fluxonium

A potential alternative to the widely used transmon qubit is the fluxonium circuit, which has desirable coherence properties when operated at half flux [1]. In contrast to the transmon there are few proposed two qubit gates for the fluxonium, a critical component for quantum computing. One popular two qubit gate for the transmon is the cross resonance (CR) gate, achieved by irradiating the control qubit at the target qubit frequency. This scheme has been shown to achieve high fidelities above 0.99 for transmons [2]. The CR gate is limited by low anharmonicities, forcing longer gate times to avoid leakage to noncomputational states. Fluxonium, having a much larger anharmonicity, has an advantage over the transmon in this respect. We propose a scheme to drive a CR gate in two fluxonium qubits coupled via an on-chip cavity and present the experimental progress in this effort.
[1] L. B Nguyen, et. al, Phys. Rev. X , (2019)
[2] S. Sheldon, et. al, Phys. Rev. A (2016).