Toffoli Netlist and QCA implementations for existing four variable reversible gates: a comparative analysis

With CMOS reaching its fundamental physical heat threshold limits, reversible logic has emerged as a viable alternative due to its heat arresting attributes. CMOS started witnessing frequency issues with maximum clocking achieved in GHz. Quantum-Dot Cellular Automata (QCA) has already promised THz clocking speeds although in the nascent form. These two domains have set the stage for information lossless substitution of CMOS in near future. QCA implementation provides a realizable implementation of the theoretical reversibility concept. Till date several four variable application specific reversible gates have been proposed but they lack relevant quantum mapping using QCA. This paper proposes both the implementations—Toffoli Netlist designs for the gates using positive control lines (optimized designs using negative control lines wherever possible) and implementations using Quantum-Dot Cellular Automata. The relevant quantum metrics have also been provided for the respective implementations. We also provide the complexity analysis of the four variable reversible gates based on Hamming Distance. This paper is intended to serve as a benchmark for optimized gate choice from among the existing four variable reversible gates for complex Boolean realizations.