High-fidelity two-qubit gates at scale are a key requirement to realize the full promise of quantum computation and simulation. The advent and use of coupler elements to tunably control two-qubit interactions has improved operational fidelity in many-qubit systems by reducing parasitic coupling and frequency crowding issues. Nonetheless, two-qubit gate errors still limit the capability of near-term quantum applications. The reason, in part, is that the existing framework for tunable couplers based on the dispersive approximation does not fully incorporate three-body multilevel dynamics, which is essential for addressing coherent leakage to the coupler and parasitic longitudinal ($ZZ$) interactions during two-qubit gates. Here, we present a systematic approach that goes beyond the dispersive approximation to exploit the engineered level structure of the coupler and optimize its control. Using this approach, we experimentally demonstrate CZ and $ZZ$-free iSWAP gates with two-qubit interaction fidelities of $99.76\pm 0.07\%$ and $99.87\pm 0.23\%$, respectively, which are close to their $T_1$ limits.

中文翻译：

---

使用可调谐耦合器实现高保真 CZ 和 ZZ-Free iSWAP 门

大规模高保真双量子位门是实现量子计算和模拟的全部承诺的关键要求。通过减少寄生耦合和频率拥挤问题，耦合器元件的出现和使用可调谐控制两个量子位交互，提高了多量子位系统的操作保真度。尽管如此，两量子位门错误仍然限制了近期量子应用的能力。部分原因是基于色散近似的可调谐耦合器的现有框架没有完全包含三体多级动力学，这对于解决耦合器的相干泄漏和寄生纵向至关重要。$ZZ$) 两个量子位门期间的相互作用。在这里，我们提出了一种超越色散近似的系统方法，以利用耦合器的工程级结构并优化其控制。使用这种方法，我们通过实验证明了 CZ 和$ZZ$具有两个量子比特交互保真度的免费 iSWAP 门 $99.76\pm 0.07\%$ 和 $99.87\pm 0.23\%$, 分别接近它们的 ${吨}_1$ 限制。