Scalable fluxonium-transmon architecture for error-corrected quantum processors

We propose a hybrid quantum computing architecture composed of alternating fluxonium and transmon qubits, which are coupled via transmon tunable couplers. We show that this system offers excellent scaling properties, characterized by engineered zero Z Z crosstalk in the idle regime, a substantial reduction of level-crowding challenges through the alternating arrangement of different qubit types within the lattice, and parameter regimes that circumvent the capacitive loading problem commonly associated with fluxoniums. In numerical simulations, we show a parametrically driven CZ gate that achieves a closed-system infidelity that is orders of magnitude below the coherence limit for gate durations ≳ 30 ns using a two-tone flux pulse on the tunable coupler. Furthermore, we show that this gate scheme retains its fidelity in the presence of multiple spectator qubits, making it a scalable solution for large lattices. Moreover, for the implementation of error correcting codes, our approach can leverage the long coherence times and large nonlinearities of fluxoniums as data qubits, while fixed-frequency transmons with established readout techniques can serve as measurement ancillae.