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New quantum entanglement record, but still no Schrödinger’s Cat

Your average cat contains more than a hundred million billion billion atoms. So that’s how many atoms would need to be ‘entangled’ via quantum mechanics to realise Schrödinger’s famous thought experiment, in which the random decay of a single atom could cause a cat in a box to be somehow alive and dead at the same time. We’re not quite there yet, but researchers at the University of Geneva in Switzerland have announced a dramatic step in this direction by creating and verifying a single quantum state of 16 million atoms. While the entanglement of pairs of particles is a common feat in laboratories, multi-particle entanglement is more complex and the previous record was a mere 2900 atoms. The achievement was “a side project” according to Florian Fröwis, the lead author of a paper describing the research in Nature Communications. It grew from work to develop a ‘quantum memory’ device that can store single photons for use in futuristic communications networks. “We always had the suspicion that the storage of a single photon should create entanglement between a large number of atoms,” he says. The quantum memory device is based on a special crystal made of the exotic-sounding yttrium orthosilicate, doped with atoms of neodymium. When the crystal absorbs photons, information about their energy and direction is stored in the relationships between the atoms in the crystal. This means it can later re-emit photons that are identical to those that came in. When the crystal absorbs only a single photon, however, things get strange. The crystal will still re-emit a photon that is exactly the same as the one that went in, which still means that information about the photon must be stored in the relationship between the atoms. However, a single photon can only be absorbed by a single atom, not by a many at once. What’s going on? The atoms in the crystal have become entangled: it no longer makes sense to talk about them as individual particles, but only to talk about the system as a whole.

Read More: Cosmos

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