Quantum information can be stored in the polarization of light which can be compared with an ordinary computer’s storage of information in bits consisting of the numbers 0 and 1. But a quantum bit cannot be stolen without it being discovered as it only contains a single photon. Such a stream of single photons can be used for secure transmission of information.

By using a laser to excite a nitrogen vacancy center in diamond, Mikhail Lukin and colleagues, Harvard University, USA, have demonstrated quantum entanglement between the nitrogen impurity and a single photon. The oscillations of the emitted photon are entangled with the spin of the electrons in the impurity and this entanglement can be used to send quantum information over long distances.

This represents a significant step toward intermediate stations, or nodes, that are able to store and process quantum information.

• Quantum entanglement between an optical photon and a solid-state spin qubit
  E. Togan, Y. Chu, A. S. Trifonov, L. Jiang, J. Maze et al.,
  Nature 2010, 466, 730–734.
  DOI: 10.1038/nature09256