Optimization of Reversible Logic Networks with Gate Sharing

Logic synthesis for quantum computing aims to transform a Boolean logic network into a quantum circuit. A conventional two-stage flow first synthesizes the given Boolean logic network into a reversible logic network composed of reversible logic gates. Then, it maps each reversible logic gate into quantum gates to generate a quantum circuit. The state-of-the-art method for the first stage takes advantage of the lookup-table (LUT) mapping technology for FPGAs to decompose the given Boolean logic network into sub-networks, and then maps the sub-networks into reversible logic networks. Although every sub-network is well synthesized, we observe that the reversible logic networks could be further optimized by sharing the reversible logic gates belonging to different sub-networks. Thus, in this paper, we propose a new optimization method for the reversible logic networks by sharing gates. We translate the problem of extracting shareable gates to the exclusive-sums-of-product term optimization problem. The experimental results show that the proposed method successfully optimizes the reversible logic networks generated by the LUT-based method. It is able to reduce an average of approximately 4% of quantum gate cost without increasing the number of ancilla lines for a set of IWLS 2005 benchmarks.