Illustration of ultracold fermionic atoms in an optical lattice potential. The atoms tended to tunnel into wells with others that had opposite spins. After a while, a line of atoms spontaneously organized itself, with the spins in a non-random pattern, revealing a signature of quantum magnetism.
Using super-chilled atoms, physicists have for the first time observed a weird phenomenon called quantum magnetism, which describes the behavior of single atoms as they act like tiny bar magnets.
Quantum magnetism is a bit different from classical magnetism, the kind you see when you stick a magnet to a fridge, because individual atoms have a quality called spin, which is quantized, or in discrete states (usually called up or down). Seeing the behavior of individual atoms has been hard to do, though, because it required cooling atoms to extremely cold temperatures and finding a way to "trap" them.
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