Trapped ion's photon transmission over 11 km over existing in-ground telecom fiber network

The transmission through existing telecom fiber infrastructure of photons emitted from quantum memories offers a means for implementing quantum information protocols between remotely located nodes. Trapped ions are excellent quantum networking nodes [1, 2] but their photon transmission distance in free space or in telecom fibers has been limited until recent integration with quantum frequency conversion (QFC) techniques [3, 4]. Here, we send photons emitted from a trapped 138Ba+ ion through an 11.2 km loop of optical telecom fiber linking our Army Research Lab quantum networking node [5] located at the University of Maryland (UMD) with the UMD Discovery Lab located 4.8 km driving-distance away. We perform two stages of QFC to convert 493 nm photons to telecom photons within the o-band regime [6] and show the preservation of the photon’s temporal profile before and after transmission. Prior long-haul networking experiments employed fiber spools [7]. Implementation within telecom fiber infrastructures [8, 9] laid in/above ground offers in-situ network testing. Our work is the longest known transmission of photons from a trapped ion over such a telecom fiber network and serves as a testbed for quantum networking protocols.