Jaume Cunill-Subiranas

A magnetic field is like a shadow cast by an object: it changes with the shape of the source. But if you put a lens in the path of light, you can alter the shadow. Here, the authors devised a 'lens' for magnetic fields — an assembly of ordinary materials with different magnetic permeabilities (their ability to let the field through).

A magnetic field holds a tiny particle in mid-air, like an invisible dance partner. A special tuning of the field creates a trap with two "positions." In the ordinary world, a dancer occupies only one, but in the quantum world — both at once. Physicists have learned to achieve this for dust grains weighing trillionths of a gram.