Communication through optical fibers has revolutionized the way people access information and has given rise to the network of connected computer nodes known as the internet. The photons that traverse the fibers are also nearly ideal carriers of quantum information: They are easy to entangle in polarization, amplitude and phase, or other degrees of freedom; they are easy to detect; and they can propagate quickly over large distances with little attenuation. Today physicists are developing the technologies needed for a quantum version of the information network, which might be used for, among other applications,long-distance cryptography, distributed quantum computing, and remote sensing.
Still in their infancy, the building blocks for those ambitions include compact sources of entangled pairs of single photons, efficient single-photon detectors, and devices that are able to manipulate the frequency and shape, both spatial and temporal, of the coherent wavepackets carried by single photons from node to node...
