Measuring the EDM requires some ingenuity. Carrying the spinning top analogy further: just as the axis of a spinning top precesses (rotates slowly about the vertical) in a gravitational field, so the neutron's magnetic dipole moment makes the neutron spin axis precess in an external magnetic field. When an electric field is added to the magnetic one, the EDM will interact with it and will make the precession either speed up or slow down, albeit very slightly, and this should be able to be measured.

This is what our experiment at ILL tries to do. The neutrons are produced in the facility's nuclear reactor, slowed down until their top speed is just a few metres per second and then collected and stored in a special quartz bottle for several hundreds of seconds. The electric field is produced by applying 100,000 volts to the lid of the bottle, while the bottom of the bottle is earthed; the voltage is periodically changed from positive to negative and back, to reverse the electric field direction. The precession rate is then measured using the nuclear magnetic resonance (NMR) methods developed by one of the group's former collaborators, Nobel prizewinner Norman Ramsey. Any slowing down or speeding up of the precession rate that coincides with the changes in direction of the electric field is evidence of an EDM.