When two atoms are suitably prepared, one can be used to control the quantum state of the other, even if they are several micrometres apart － a considerable distance for atoms. These results, reported online this week in Nature Physics, should enable controlled manipulation of quantum entanglement. This is the key ingredient in protocols that harness the properties of quantum physics for applications like computation and communication.
It has been predicted that when individual ‘Rydberg’ atoms －neutral atoms with electrons in highly excited states － strongly interact, certain quantum transitions that are possible for a single particle are forbidden for the collective. This mechanism has now been independently observed for pairs of individually trapped Rydberg atoms by the groups of Antoine Browaeys and Mark Saffman. In these settings, both the individual atoms as well as the interaction between them can be controlled, meaning that they should be a suitable platform for practical applications.