Five-Photon Entanglement

Five-photon entanglement has been achieved by physicists at the University of Science and Technology in China. Entanglement is perhaps the weirdest of all aspects of quantum behavior. If several particles are entangled, this means that they participate in a single quantum state which can be in several unique states at the same time. Furthermore, the measurable properties of the particles, such as their spins, will be correlated, even if subsequently the particles are located at great distances from each other and the properties measured separately. Previously the greatest degree of full quantum entanglement came in experiments involving four particles. (For the case of four ions held in a trap, see Update 475.)

The Chinese researchers entangle two pairs of photons, and then entangle these with yet another single photon. (Zhao et al., Nature, 1 July 2004.) The progress from four to five entangled particles is significant since apparently the handling of quantum information (such as in a quantum computer) with a built-in error correction process would require the manipulation of five entangled particle engineered to serve as qubits (see, for example, Laflamme et al., Physical Review Letters, 1 July 1996.)