Scalable Fluxonium-Transmon Architecture for Error Corrected Quantum Processors

TL;DR

This paper introduces a scalable hybrid quantum architecture combining fluxonium and transmon qubits with tunable couplers, achieving low crosstalk, high-fidelity gates, and suitability for error correction in large quantum processors.

Contribution

It presents a novel hybrid fluxonium-transmon architecture with engineered crosstalk suppression and a robust, high-fidelity CZ-gate scheme suitable for scalable quantum error correction.

Findings

Achieves low $ZZ$-crosstalk in idle regime

Demonstrates high-fidelity CZ-gate with infidelity below coherence limit

Maintains gate fidelity in presence of spectator qubits

Abstract

We propose a hybrid quantum computing architecture composed of alternating fluxonium and transmon qubits, that are coupled via transmon tunable couplers. We show that this system offers excellent scaling properties, characterized by engineered zero $ZZ$-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 $\gtrsim 30\,\rm{ns}$ using a two-tone flux pulse on the tunable coupler. Furthermore, we show that this gate scheme retains its fidelity in the presence of 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 non-linearities of fluxoniums as data qubits, while fixed-frequency transmons with established readout techniques can serve as measurement ancillas.