Optimization of reversible circuits using triple-gate templates at quantum gate level

Abstract

The paper presents an approach for optimizing a reversible netlist consisting of multiple-control Toffoli (MCT) gates with the objective of reducing quantum cost. The MCT gates are first decomposed into smaller gates with up to three control lines, and then a template matching method is applied on the netlist for optimization. The templates are constructed by considering all possible 3-gate sequences with up to four lines. This work constitutes an extension of a previous work by Dueck et al., where 2-gate sequences were considered in the templates. The input gate netlists are generated from the reversible benchmarks available in RevLib, followed by Barenco decomposition to produce Toffoli gates with at most three control connections. The proposed approach is applied on these netlists, and the final quantum cost calculated. Experimental results on standard benchmarks show that the method can lead to reductions in quantum cost.