Creation of a six-atom ‘Schrödinger cat’ state

Schrödinger's atomic cats Schrödinger's hypothetical cat was both dead and alive thanks to a paradox of quantum mechanics, in which a system exists in two or more states at once in a ‘superposition’ of entangled states. Creating this situation experimentally is very difficult, especially for systems made up of many particles, as interactions with the environment destroy superposition in a process called decoherence. So far, entangled states of just a handful of atoms or photons have been achieved. Now, two groups have extended the limits of quantum state engineering by creating the largest entangled atomic systems to date. Working with atoms held in an ion trap by an electromagnetic field to limit decoherence, a team from the National Institute of Standards and Technology in Boulder, Colorado, has created ‘cat states’ of up to six beryllium atoms. A second group, based at Innsbruck University in Austria, has achieved a similar feat by making a related entangled state, a ‘W state’, containing up to eight particles. As the states are created ‘on demand’ and should be scalable to many more particles, there is hope that this technology will pave the way for building a large-scale quantum computer.