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.
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. “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.
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.
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.
Physicists at the University of Calgary have also just published research using a similar technique, in which they demonstrate the entanglement of more than 200 groups of atoms, with each group itself containing more than a billion atoms.