A Cage of Light: How an Ion Gets Stuck in a Lattice
An ordinary magnet makes a compass needle turn, but it doesn't stop the needle from moving forward. But if you twist a magnetic field into a knot, it can trap a particle in place, like a snare. This phenomenon is called an 'Aharonov–Bohm cage': the particle's waves cancel each other out at some points and reinforce at others, leaving only tiny 'islands' where it can exist.