Microwave activated two-qubit gate for fluxonium qubits via a tunable-transmon coupler*

Qubit lifetimes in superconducting transmon based quantum computers are a leading cause of gate infidelity. Furthermore, the transmon’s anharmonicity gives rise to frequency crowding on multi-qubit devices and limits the gate speed. The fluxonium qubit is a promising alternative to transmons, with coherence times reaching the order of milliseconds and anharmonicities on the order of gigahertz. In this work, we present a device containing two fluxonium qubits connected by a tunable-transmon coupler. By utilizing the higher levels of the fluxonium qubits and the transmon excited state, we explore the potential of a microwave activated CPHASE gate. We present results on a device designed to operate in a parameter space that has large qubit-to-qubit couplings and a reduced always-on ZZ interaction. This architecture is expected to facilitate faster, higher fidelity two-qubit gates.