Unlocking a fast adiabatic CZ gate and exact residual $ZZ$ cancellation between fixed-frequency transmons using a floating tunable coupler

Quantum Physics [Submitted on 6 Apr 2026] Unlocking a fast adiabatic CZ gate and exact residual ZZ cancellation between fixed-frequency transmons using a floating tunable coupler Angela Q. Chen, Xian Wu, Sarah Strong, Stefano Poletto Tunable couplers in superconducting qubit architectures enable strong qubit-qubit interactions for two-qubit gates while suppressing unwanted coupling during single-qubit operations. However, achieving low error rates for fast two-qubit gates remains challenging, as suppressing leakage and non-adiabatic errors typically requires specialized qubit, coupler, or pulse designs, often at the expense of an idling ZZ=0 condition. In this work, we demonstrate that a symmetric floating tunable coupler provides a natural platform for fast, high-fidelity adiabatic controlled-Z (CZ) gates. Its favorable energy-level structure eliminates the conventional trade-off between rapid conditional-phase accumulation and adiabatic evolution while preserving exact cancellation of residual ZZ interaction at idling. This architecture exhibits intrinsic robustness to non-adiabatic transitions, even under simple flux modulation waveforms. To push performance at short gate durations, where maintaining adiabaticity becomes more challenging despite the favorable level structure, we introduce pulse-shaping techniques based on the instantaneous adiabatic factor that further suppress non-adiabatic errors. We experimentally realize a 24 ns adiabatic CZ gate with fidelity exceeding 99.9% and stable operation over several hours. Subjects: Quantum Physics (quant-ph) Cite as: arXiv:2604.05048 [quant-ph]   (or arXiv:2604.05048v1 [quant-ph] for this version)   https://doi.org/10.48550/arXiv.2604.05048 Focus to learn more Submission history From: Angela Q. Chen [view email] [v1] Mon, 6 Apr 2026 18:01:14 UTC (1,088 KB) Access Paper: HTML (experimental) view license Current browse context: quant-ph < prev   |   next > new | recent | 2026-04 References & Citations INSPIRE HEP NASA ADS Google Scholar Semantic Scholar Export BibTeX Citation Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer (What is the Explorer?) Connected Papers Toggle Connected Papers (What is Connected Papers?) Litmaps Toggle Litmaps (What is Litmaps?) scite.ai Toggle scite Smart Citations (What are Smart Citations?) Code, Data, Media Demos Related Papers About arXivLabs Which authors of this paper are endorsers? | Disable MathJax (What is MathJax?)