Entanglement of single-atom quantum bits at a distance

The phenomenon of entanglement is a key concept in quantum information science. Atomic systems are promising candidates for quantum 'memories'. These in turn can be coupled and entangled by the exchange of photons, providing the basis of a quantum information processor. The signature of entanglement between remotely located atomic ensembles was recently demonstrated. Now Moehring et al. have achieved entanglement between two single-ion quantum memories separated by a metre. The use of single ions, rather than atomic ensembles, has certain advantages for subsequent quantum operations.