For an isolated cell these 2 states will have the same energy. However for an array of cells, the state of each cell is determined by its interaction with neighboring cells through the Coulomb interaction. The tunneling energy between two neighboring sites is designated by t, while a is the near-neighbor distance. If the barriers between cells are sufficiently high, the electrons will be well localized on individual dots. The Coulomb repulsion between the electrons will tend to make them occupy antipodal sites in the square a shown in Fig. 2 .
Coulombic repulsion causes the electrons to occupy antipodal sites within the cell.
The two polarization states of the cell will not be energetically equivalent if other cells are nearby. Consider two cells close to one another as shown in the inset of Fig. The cell-cell response A Majority Gate Fig. 4 shows the fundamental QCA logical device, a three-input majority gate, from which more complex circuits can be built. The device cell has its lowest energy state if it assumes the polarization of the majority of the three input cells.