A Fluxonium Architecture for QEC, Part 2: Extensible and Spectator-Error-Free Two-Qubit Gate Scheme

Fault-tolerant quantum computing remains a central goal of the superconducting qubit community, with fluxonium qubits showing significant promise due to their extended coherence times [1] and recent demonstrations of high-fidelity single-qubit [2] and two-qubit gates [3]. Despite this progress, two major challenges must be addressed before fluxonium qubits can be widely adopted for quantum error correction (QEC) applications: the development of fast, high-fidelity, quantum non-demolition measurements and the demonstration of an extensible two-qubit gate scheme resilient to spectator errors.

In this talk, we present an extensible scheme for two-qubit gates in fluxonium qubits. Recent work has focused on microwave-activated conditional-phase (MAP) gates, utilizing a transmon coupler to achieve fast gates while suppressing residual (ZZ) couplings. However, such schemes often suffer from spectator-qubit errors, making them impractical for large qubit arrays. Furthermore, the relatively large charging energy of the fluxonium makes it challenging to support multiple connections. We present a gate scheme that addresses these issues in the presence of nearest-neighbor connectivity. Given the strict bounds on correlated error sources required for QEC, we believe that solving these issues highlights the potential of the fluxonium qubit for such applications.

[1] A. Somoroff, et al., PRL, 2023

[2] D. Rower, L. Ding, et al., arXiv:2406.08295, 2024

[3] L. Ding, et al., PRX, 2023