Tomography of Distant Single Atoms

Entanglement of distant quantum memories forms the building block of quantum networks. Neutral atoms with long coherence times are sought for candidates for quantum network links (QNLs). Our experiment with two nodes, 400 m apart, employs single optically trapped Rubidium-87 atoms as quantum memories. Via excitations, entanglement between the atom and spontaneously emitted single photons is created in both traps. Using single-mode fibers, the photons are interfered in a Bell-state measurement thereby swapping the entanglement from the two atom-photon pairs to the atoms with a projective measurement. A new collection setup [1] allows for an increased entanglement event rate of ∼1/20 Hz allowing detailed state analysis and reconstruction of the entangled state.