Kilometer-scale ion-photon entanglement with a metastable qubit
Phys. Rev. A 113, 012615 – Published 20 January, 2026
DOI: https://doi.org/10.1103/nc84-zjp3
Abstract
We demonstrate entanglement between the polarization of an infrared photon and a metastable ion qubit. This entanglement persists after transmitting the photon over a long commercial fiber deployed in an urban environment. Tomography of the ion-photon entangled state yields a fidelity of 0.949(4) within the laboratory and 0.929(5) after fiber transmission, not corrected for readout errors. Our results establish the strontium ion as a promising candidate for metropolitan-scale quantum networking based on an atomic transition at , a wavelength compatible with existing telecom fiber infrastructure.
