Arthur Christianen

A lone potassium atom enters a dense cloud of sodium atoms cooled to near absolute zero. Such a medium is called a Bose–Einstein condensate — all particles merge into a single quantum wave. One might expect the impurity to simply pick up a single neighbor and form a pair. But the experiment showed something else.

A polar molecule is like a tiny dumbbell with opposite charges at its ends. Normally, such particles quickly stick together or fly apart when they meet — electric forces are too strong. But the authors of the work found a way to turn this aggressiveness into a controlled game.