In the late 1990s, physicists figured out how to adjust the interaction between atoms in cold, dense gases. Provided the atoms’ energy levels are favorable, a magnetic field suffices to tune the interaction from weak to strong or from repulsive to attractive.

With that tuning ability came the prospect of exploring few- and many-body phenomena over ranges of conditions far wider than available in a given crystal, liquid, or nucleus. Antiferromagnetism and high-Tc superconductivity await their realization in cold atomic gases, but Cooper pairing, Efimov trimers, Mott insulators, and the Berezinskii-Kosterlitz-Thouless transition have already been observed.

Now, two independent groups have added another coherent phenomenon to the cold-atom repertoire: antibunching. Antibunching is the fermionic equivalent of bosonic bunching. Half a century ago, Robert Hanbury Brown and Richard Twiss sought and found bunching in photons from a mercury discharge lamp.

The two cold-atom groups used different techniques. Immanuel Bloch...

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