Method for fractional charge search using ferromagnetic levitation

A new method of ferromagnetic levitation has been developed for use in searches for stable fractional charge on bulk matter. A 300 μ diameter steel ball is suspended by permanent magnetic so that it is passively stable, with a high mechanical Q, in the vertical direction. The ball is held in both horizontal directions with critical damping by two independent feedback systems. These perpendicular servos sense ball position optically and use electromagnetic coils to exert force on the ball. Charge is measured by applying an alternating vertical electric field to synchronously build up the ball motion at the ball's natural frequency of ∼ 1 Hz. The difference of rates of change of amplitude when the field is applied exactly in and out of phase with ball velocity gives a measure of charge. At present the level of noise in sensing electronics is sufficient to detect charges of e/3 with a noise background of 0.03e after 15 hours