Tunable couplers enable high-fidelity two-qubit gates leveraging high on/off coupling ratios and reduced crosstalk within a single design. We investigate a galvanically connected direct-current superconducting quantum interference device (dc SQUID) as a minimal tunable coupling element for fluxonium qubits. Comparing grounded and floating fluxonium designs, we find that the latter contains an extra sloshing mode that strongly hybridizes with the qubit modes, leading to significant static ZZ crosstalk. In contrast, the grounded design avoids this issue and allows suppression of static ZZ crosstalk using a shunting capacitor. Leveraging fast flux control, we present two schemes to implement two-qubit gates, predicting a iSWAP-like gate with 99.9% open-system fidelity in less than 6 nanoseconds assuming modest relaxation and dephasing rates.
@article{arxiv.2508.16907,
title = {Tunable Superconducting Quantum Interference Device Coupler for Fluxonium Qubits},
author = {Abhishek Chakraborty and Bibek Bhandari and D. Dominic Briseño-Colunga and Noah Stevenson and Zahra Pedramrazi and Chuan-Hong Liu and David I. Santiago and Irfan Siddiqi and Justin Dressel and Andrew N. Jordan},
journal= {arXiv preprint arXiv:2508.16907},
year = {2025}
}