A Post-Synthesis Optimization Technique for Reversible Circuits Exploiting Negative Control Lines

Recent works in the synthesis of reversible logic circuits have been motivated by ever increasing emphasis on low-power design alternatives, and recent developments in quantum computing. Although most of the synthesis approaches use multiple-control Toffoli (MCT) gates with positive control lines, a few recent works have also considered MCT gates with negative control lines resulting in better circuit realizations. Some of the works have also tried to carry out post-synthesis optimization of given MCT gate netlists with positive control lines, using template matching and similar netlist transformation techniques. However, only one work is reported that attempts to optimize netlists containing negative control MCT gates. This paper proposes an efficient optimization technique for MCT gate netlists with both positive and negative control lines, which is based on repeated applications of a small set of pairwise gate merging and replacement rules. Experiments carried out on reversible circuit benchmarks show that it is possible to achieve significant reductions in number of gates and quantum costs.