For the first time, it has been theoretically demonstrated how delta-kick collimation (DKC) — a short pulse that 'squeezes' the cloud — can cool heteronuclear Feshbach molecules to picokelvin temperatures, comparable to record atom cooling. The method works for both condensates and regular thermal ensembles, dramatically reducing expansion energy and beam angular divergence. Calculations show that internal molecular vibrations do not interfere with the process, meaning the molecules remain stable. This paves the way for molecular interferometry and tests of the equivalence of free fall.
A push at the right moment stops a swing. The delta-kick—a short laser pulse—was applied to a cloud of molecules, and it froze, like a swing after a precise kick. Molecules made of two different atoms, like a seat firmly locked to the swing’s bar, didn't fall apart during deceleration. The temperature dropped to picokelvins—trillionths of a degree above absolute zero, where motion nearly freezes and энтропия (a measure of disorder) becomes minimal. Even the internal jitter of atoms didn't disturb the stillness—like a passenger's slight swaying doesn't change the swing's motionlessness. An unexpected fact: at this temperature, the molecular cloud expands slower than grass grows. Now these nearly immobile objects are used to test the law of universal gravitation, which Галилей tested by dropping cannonballs from a tower, and Эйнштейн linked to кривизной пространства-времени. Based on them, scientists will build световую молекулярную интерферометрию—a device capable of detecting even the tiniest deviations.
🎯 At a temperature of one picokelvin, molecules move so slowly that crossing the width of a human hair would take them a full minute.