This paper reports on the successful implementation of quantum entanglement distribution and quantum state teleportation over a 14.4 km urban dark-fiber link. The link, characterized for its use as a quantum channel, underwent active polarization stabilization. Utilizing a type-II cavity-enhanced SPDC photon pair source, a ⁴⁰Ca⁺ single-ion quantum memory, and quantum frequency conversion to the telecom C-band, the researchers demonstrated photon-photon entanglement, ion-photon entanglement, and qubit state teleportation from the ion to a remote telecom photon, all across the urban fiber link.

Stephan Kucera, Christian Haen, Elena Arenskötter, Tobias Bauer, Jonas Meiers, Marlon Schäfer, Ross Boland, Milad Yahyapour, Maurice Lessing, Ronald Holzwarth, Christoph Becher, Jürgen Eschner