High-fidelity quantum state transfer and remote entanglement between superconducting fixed-frequency qubits have not yet been realized. In this study, we propose an alternative remote cross-resonance gate. Considering multiple modes of a superconducting coaxial cable connecting qubits, we must find conditions under which the cross-resonance gate operates with a certain accuracy even in the presence of qubit frequency shifts due to manufacturing errors. For 0.25- and 0.5 m cables, remote cross-resonance gates with a concurrence of >99.9% in entanglement generation are obtained even with ±10 MHz frequency shifts. For a 1 m cable with a narrow mode spacing, a concurrence of 99.5% is achieved by reducing the coupling between the qubits and cable. The optimized echoed raised-cosine pulse duration is 150–400 ns, which is similar to the operation time of cross-resonance gates between neighboring qubits on a chip. The dissipation through the cable modes does not considerably affect the obtained results. Such high-precision quantum interconnects pave the way not only for scaling up quantum computer systems but also for nonlocal connections on a chip.

中文翻译：

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超导固定频率量子位之间的远程交叉谐振门

超导固定频率量子位之间的高保真量子状态转移和远程纠缠尚未实现。在这项研究中，我们提出了一种替代远程交叉谐振门。考虑到连接量子位的超导同轴电缆的多种模式，我们必须找到即使在由于制造误差而存在量子位频移的情况下，交叉谐振门也能以一定精度运行的条件。对于 0.25 和 0.5 m 电缆，远程交叉谐振门同时 >99.9% 即使在 ±10 MHz 频移下也能获得纠缠生成。对于具有窄模式间距的 1 m 电缆，通过减少量子位和电缆之间的耦合可以实现 99.5% 的并发性。优化的回波升余弦脉冲持续时间为 150–400 ns，与芯片上相邻量子位之间的交叉谐振门的操作时间相似。通过电缆模式的耗散不会显着影响所获得的结果。这种高精度量子互连不仅为量子计算机系统的扩展铺平了道路，也为芯片上的非本地连接铺平了道路。