An ordinary top spun on a table slows down smoothly: friction with the air and the surface gradually eats away its energy. But if a top levitates in a magnetic field and barely touches anything, its rotation can behave surprisingly capriciously. That's exactly the case the experimenters described: they suspended a tiny quartz cube weighing a milligram using diamagnetic levitation — the effect where a weak magnetic field repels certain materials, keeping them from falling.

The cube was spun up with light to about 360 revolutions per minute and then left to rotate. Instead of a smooth deceleration, the speed dropped in steps. Each time the rotation frequency matched the frequency of one of the cube's internal elastic vibrations, as if the top began to 'ring' in time with its own spin, part of the energy leaked into those vibrations, and the cube abruptly lost speed. This behavior is called nonlinear mode coupling: different types of motion exchange energy not gradually but in jumps.

But the most surprising thing happened when they directed a weak counter-propagating beam of light at the cube — a tiny pressure that should have slightly braked the rotation. Instead, the cube froze at one speed and held it for about two days. This is the mechanical analog of a phenomenon known in electronics as frequency locking: an oscillator, receiving a weak signal from a neighbor, begins to oscillate in sync with it. Here, the 'neighbor' was the cube itself: its internal vibrations captured the rotation and prevented it from changing.

Such 'self-locking' opens the way to new mechanical sensors: if the cube's rotation is tied to its own vibrations, the slightest change in conditions (say, a tiny force or a change in the magnetic field) will shift that lock, and that can be detected. It's also a platform for studying complex systems where many types of motion are coupled, and for creating mechanical 'attractors'—stable states that the system naturally gravitates toward.