Near Zero-Energy Computation Using Quantum-Dot Cellular Automata

Near zero-energy computing describes the concept of executing logic operations below the (k_BT ln 2) energy limit. Landauer discussed that it is impossible to break this limit as long as the computations are performed in the conventional, non-reversible way. But even if reversible computations were performed, the basic energy needed for operating circuits realized in conventional technologies is still far above the (k_BT ln 2) energy limit (i.e., the circuits do not operate in a physically reversible manner). In contrast, novel nanotechnologies like Quantum-dot Cellular Automata (QCA) allow for computations with very low energy dissipation and hence are promising candidates for breaking this limit. Accordingly, the design of reversible QCA circuits is an active field of research. But whether QCA in general and the proposed circuits in particular are indeed able to operate in a logically and physically reversible fashion is unknown thus far, because neither physical realizations nor appropriate simulation approaches are available. In this work, we address this gap by utilizing an established theoretical model that has been implemented in a physics simulator enabling a precise consideration of how energy is dissipated in QCA designs. Our results provide strong evidence that QCA is indeed a suitable technology for near zero-energy computing. Further, the first design of a logically and physically reversible adder circuit is presented, which serves as proof of concept for future circuits with the ability of near zero-energy computing.