Long-distance entanglement distribution is the key task for quantum networks,
enabling applications such as secure communication and distributed quantum
computing. Here we report on novel developments extending the reach for sharing
entanglement between a single 87Rb atom and a single photon over long
optical fibers. To maintain a high fidelity during the long flight times
through such fibers, the coherence time of the single atom is prolonged to 7 ms
by applying a long-lived qubit encoding. In addition, the attenuation in the
fibers is minimized by converting the photon's wavelength to the telecom S-Band
via polarization-preserving quantum frequency conversion. This enables to
observe entanglement between the atomic quantum memory and the emitted photon
after passing 101 km of optical fiber with a fidelity better than
70.8±2.4%. The fidelity, however, is no longer reduced due to loss of
coherence of the atom or photon but in the current setup rather due to detector
dark counts, showing the suitability of our platform to realize city-to-city
scale quantum network links.Comment: 11 pages, 8 figures, comments are welcom