The world is filled with rotating objects—gyroscopes, magnetic spins, and more recently, qubits in quantum computers. For example, the atomic nuclei in our bodies precess at megahertz frequencies inside NMR machines. In practice, it is often desirable to return such a rotating system precisely to its starting point. At first glance, this seems impossible: after an elaborate sequence of twists and wobbles, how could one possibly retrace the path back to the origin?
The astonishing answer is that it is always possible. No matter how tangled the history of rotations, there exists a simple recipe: rescale the driving force and apply it twice. A single application is never sufficient, but applying this doubled, rescaled force guarantees an exact return. Under this operation, the spin—or the qubit, or any rotor—will unfailingly come home.
This discovery was made by Distinguished Professor Tsvi Tlusty from the Department of Physics at UNIST and Jean-Pierre Eckmann from the University of Geneva, Switzerland. Their study, published in Physical Review Letters on October 1, 2025, reveals that, despite their apparent complexity, rotations conceal a fundamental order.
