Ernst M. Rasel

A cloud of 41K87Rb molecules held in an optical trap expands like fog at dawn. Each molecule is a weakly bound pair of potassium and rubidium atoms, teetering on the brink of dissociation. Cooling such a cloud to near absolute zero without shattering the molecules has long been a challenge.

In the shaft leading to the Large Hadron Collider, an unusual tenant may soon move in: a hundred-meter vertical tube where clouds of strontium atoms will be dropped. Each cloud is cooled to near absolute zero, so the atoms move slowly and in sync, like dancers in slow motion.