Trapped atomic ions embedded in optical cavities are a promising platform to enable long-distance quantum networks and their most far-reaching applications. Here we achieve and analyze photon indistinguishability in a telecom-converted ion-cavity system. First, two-photon interference of cavity photons at their ion-resonant wavelength is observed and found to reach the limits set by spontaneous emission. Second, this limit is shown to be preserved after a two-step frequency conversion replicating a distributed scenario, in which the cavity photons are converted to the telecom $C$ band and then back to the original wavelength. The achieved interference visibility and photon efficiency would allow for the distribution and practical verification of entanglement between ion-qubit registers separated by several tens of kilometers.

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来自捕获离子量子网络节点的不可区分的光子

嵌入光腔中的被困原子离子是一个有前途的平台，可以实现长距离量子网络及其最广泛的应用。在这里，我们实现并分析了电信转换离子腔系统中的光子不可区分性。首先，观察到腔光子在其离子共振波长处的双光子干涉，并发现达到了自发发射设定的极限。其次，该限制显示为在复制分布式方案的两步频率转换后得以保留，在该方案中，将腔体光子转换为电信$C$波段，然后回到原始波长。所获得的干扰可见度和光子效率将允许相隔数十公里的离子量子比特寄存器之间的纠缠分布和实际验证。