The neutron is a particle with no electric charge, making it tricky to catch: it slips through instruments like a bullet through fog. In typical experiments, it gets just one pass through a crystal, and all measurements must fit into that instant.

A new idea is to make the neutron loop inside a trap, like a ball bouncing between two walls. This uses a neutron reflecting off perfectly smooth silicon plates. The plates are arranged so the neutron bounces off them again and again (up to 10,000 times) and stays inside for several seconds.

Such a delay sharply boosts measurement sensitivity. The authors calculated that one effect related to the neutron's spin in an electric field could be detected 10 times more precisely than in recent experiments. And the search for the neutron's electric dipole moment, a tiny shift of charge inside the particle, could reach a sensitivity of 10⁻²⁷ e·cm. That's a billion times smaller than the size of an atom.

The silicon trap is like a maze with mirrored walls, where the particle can't find the exit and thus reveals its secrets. In the future, such devices could help test whether mirror symmetry is violated in the microcosm and refine the neutron's lifetime.