Physicists Create First Long-Distance Quantum Link: "In the past, we have built networks that can communicate quantum information, but convert it into classical form at the network switching points. [The researchers] report preliminary experiments towards forming a network in which the information remains in quantum form..."
As simple as this may sound, the researchers still needed a complete lab room full of lasers, optical elements, and other equipment for each node. Each atom sat between two highly reflective mirrors 0.5 mm apart, which form an "optical cavity." By applying an external laser to atom A, Ritter's team caused a photon emitted by that atom to escape from its cavity and travel through a 60-meter-long optical fiber to the cavity across the street. When the photon was absorbed by atom B, the original quantum information from the first atom was transferred to the second. By starting with just the right state of the first atom, the researchers could entangle the two atoms. According to the researchers, the entanglement could in principle be extended to a third atom, which makes the system scalable to more than two nodes.