Entanglement, one of the most striking features of quantum mechanics, leads to strong correlations between the various components of a physical system, regardless of the distance separating them. However, entanglement is fragile, and to use quantum protocols over long distances the channel has to be divided into many segments and entanglement generated and stored into material systems before connecting them all together. The significant achievement of the Caltech group is that they have demonstrated an initial version of one of these segments. The experiment involves two quantum memories separated by three meters, each consisting of two atomic ensembles separated by one millimeter. The ensembles are clouds of about 100,000 cooled cesium atoms. With real-time control of the quantum states, entanglement is generated, stored into the atoms, and finally converted to photons on demand. The released entanglement is in an appropriate form for quantum communication applications.
Credit: Zina Deretsky