Physicists have used a quantum connection Albert Einstein called “spooky action at a distance” to link 500,000 atoms together so that their fates were entwined. The atoms were connected via “entanglement,” which means an action performed on one atom will reverberate on any atom entangled with it, even if the particles are far apart. The huge cloud of entangled atoms is the first “macroscopic spin singlet,” a new state of matter that was predicted but never before realized.
Entanglement is a consequence of the strange probabilistic rules of quantum mechanics and seems to permit an eerie instantaneous connection over long distances that defies the laws of our macroscopic world (hence Einstein’s “spooky” remark). A spin singlet is one form of entanglement where multiple particles’ spins—their intrinsic angular momentum—add up to 0, meaning the system has zero total angular momentum.
The experimenters worked with rubidium atoms, which have a constant spin value of 1. (All particles have an unchanging spin value, a quantum characteristic that is always given in numbers without units.) The only way for a group of these atoms to have spins that add up to zero—the requirement for a spin singlet—is if the direction of their spins cancel one another out. And once two or more atoms are entangled in a spin singlet, their spins will always equal zero. That means that, bizarrely, if the direction of one atom’s spin is altered, its entangled fellows will change their spins accordingly, and instantaneously, to preserve the sum of zero total spin.