Measurement-induced entanglement for excitation stored in remote atomic ensembles

Two groups this week report a significant step on the long road to quantum computing: the storage and retrieval of single photons onto and from atomic quantum memories. Chanelière et al. produced single photons from an atomic quantum memory in one lab, transported them through a 100-metre-long optical fibre and stored them for a time in a second memory. The atomic excitation was then converted back into a single photon. Previously, weak coherent laser pulses have been stopped and retrieved in atomic media, but single photons are ideal for realizing quantum bits. Eisaman et al. report a similar approach, using the coherent control technique known as electromagnetically induced transparency for the generation, transmission and storage of single photons. A third paper reports progress in another technology critical for quantum communication and computation: the storage and distribution of entangled quantum states. Chou et al. have achieved entanglement between two samples of atoms separated by 2.8 metres that jointly store one quantum bit of information.