Indistinguishable photons from a trapped-ion quantum network node

TL;DR

This paper demonstrates highly indistinguishable photons from a trapped-ion quantum network node, even after telecom wavelength conversion, paving the way for long-distance quantum communication.

Contribution

It shows photon indistinguishability preservation through frequency conversion in an ion-cavity system, enabling scalable quantum networks.

Findings

Photon interference reaches limits set by spontaneous emission.

Indistinguishability preserved after telecom wavelength conversion.

Potential for entanglement distribution over tens of kilometers.

Abstract

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.