A new phenomenon of quantum-dot cellular automata

If an external point charge and the movable charges of an isolated quantum-dot cellular automata （QCA） cell have the same polarity, the point charge greatly affects the polarization （P） of the cell only when it is in a narrow band with periodically changing width. The center of the band is on a radius R circle. The ratio of R to the electric charge （q） is a constant determined by the parameters of the cell. A QCA cell can be used as charge detector based on the above phenomenon.