Symmetric versus asymmetric charge neutralization in quantum-dot cellular automata

Quantum-dot cellular automata (QCA), a method for computing through energy relaxation via quantum mechanical effects, promise high speed, very low power, and extremely high density. The first steps in implementing QCA have been taken; a small device has recently been manufactured and is logical switching behavior demonstrated. This paper investigates the behaviors of some proposed QCA primitives: wires, crossings, corners, and logic gates, under two charge neutralization schemes. While these primitives work well under the originally proposed charge neutralization scheme, it is shown that with a more realistic scheme, most of the primitives can fail outright, show a preference for a undesirable logical state, or show a decrease in the energy gap between the ground state and other excited states. Redesigned primitives are presented which may perform as well, or better, under either neutralization scheme.