While the common practice of decomposing general quantum algorithms into a collection of single- and two-qubit gates is conceptually simple, in many cases it is possible to have more efficient solutions where quantum gates engaging multiple qubits are used. In the noisy intermediate-scale quantum (NISQ) era where a universal error correction is still unavailable, this strategy is particularly appealing since it can significantly reduce the computational resources required for executing quantum algorithms. In this work, we experimentally investigate a three-qubit Controlled-CPHASE-SWAP (CCZS) gate on superconducting quantum circuits. By exploiting the higher energy levels of superconducting qubits, we are able to realize a Fredkin-like CCZS gate with a duration of 40 ns, which is comparable to typical single- and two-qubit gates realized on the same platform. By performing quantum process tomography for the two target qubits, we obtain a process fidelity of 86.0% and 81.1% for the control qubit being prepared in ∣0〉 and ∣1〉, respectively. We also show that our scheme can be readily extended to realize a general CCZS gate with an arbitrary swap angle. The results reported here provide valuable additions to the toolbox for achieving large-scale hardware-efficient quantum circuits.

虽然将通用量子算法分解为单量子位门和两个量子位门的集合的常见做法在概念上很简单，但在许多情况下，使用涉及多个量子位的量子门可能会获得更有效的解决方案。在仍然无法实现通用纠错的嘈杂中尺度量子（NISQ）时代，这种策略特别有吸引力，因为它可以显着减少执行量子算法所需的计算资源。在这项工作中，我们通过实验研究了超导量子电路上的三量子位受控 CPHASE-SWAP (CCZS) 门。通过利用超导量子位的较高能级，我们能够实现持续时间为 40 ns 的类似 Fredkin 的 CCZS 门，这与在同一平台上实现的典型单量子位门和两个量子位门相当。通过对两个目标量子位进行量子过程层析成像，我们在 ∣0> 和 ∣1> 中制备的控制量子位的过程保真度分别为 86.0% 和 81.1%。我们还表明，我们的方案可以很容易地扩展以实现具有任意交换角度的通用 CCZS 门。这里报告的结果为实现大规模硬件高效量子电路的工具箱提供了有价值的补充。