When two superconductors are separated by a weak link, a supercurrent is carried by Andreev bound states formed by the phase-coherent reflection of electrons and their time-reversed partners. The two levels associated with a single, highly transmissive Andreev bound state can serve as a qubit due to the potentially large energy difference with the next bound state. Although coherent manipulation of these so-called Andreev pair qubits has been demonstrated, long-range qubit–qubit coupling, which is necessary for advanced quantum computing architectures, has not yet been achieved. Here, we demonstrate coherent remote coupling between two Andreev pair qubits mediated by a microwave photon in a superconducting cavity coupler. The latter hosts two modes that are engineered to have very different coupling rates to an external port. The strongly coupled mode can be used to perform a fast read-out of each qubit, while we use the weakly coupled mode to mediate the coupling between the qubits. When both qubits are tuned into resonance with the latter mode, we find excitation spectra with characteristic avoided crossings. We identify two-qubit states that are entangled over a distance of 6 mm. This work establishes Andreev pair qubits as a compact and scalable approach to developing quantum computers.

当两个超导体被一个薄弱环节隔开时，安德烈耶夫束缚态会携带超电流，该束缚态由电子及其时间反转的伙伴的相位相干反射形成。与单个高度透射的 Andreev 绑定态相关的两个级别可以用作量子比特，因为与下一个绑定态可能存在较大的能量差异。尽管已经证明了这些所谓的 Andreev 对量子比特的相干操作，但尚未实现高级量子计算架构所必需的远程量子比特-量子比特耦合。在这里，我们展示了由超导腔耦合器中的微波光子介导的两个 Andreev 对量子比特之间的相干远程耦合。后者具有两种模式，这些模式被设计为与外部端口具有非常不同的耦合率。强耦合模式可用于执行每个量子比特的快速读出，而我们使用弱耦合模式来调解量子比特之间的耦合。当两个量子比特都调谐到与后一种模式的谐振时，我们发现激发光谱具有特征性避免的交叉。我们确定了在 6 mm 距离内纠缠的双量子比特状态。这项工作将 Andreev 对量子比特确立为开发量子计算机的一种紧凑且可扩展的方法。