SSR: A Swapping-Sweeping-and-Rewriting Optimizer for Quantum Circuit Transformation

Quantum circuit transformation (QCT), necessary for adapting any quantum circuit to the qubit connectivity constraints of the NISQ device, often introduces numerous additional SWAP gates into the original circuit, increasing the circuit depth and thus reducing the success rate of computation. To minimize the depth of QCT circuits, we propose a Swapping-Sweeping-and-Rewriting optimizer. This optimizer rearranges the circuit based on generalized gate commutation rules via a genetic algorithm, extracts subcircuits consisting of CNOT gates using a circuit sweeping technique, and rewrites each subcircuit with a functionally equivalent and depth-optimal circuit generated by an SAT solver. Experimental results demonstrate that, compared with existing post-QCT optimization approaches such as CBIR and Q-Synth, SSR achieves superior performance, improving circuit depth by up to 29.04% and 16.59% on average across all benchmark circuits, whereas the depth reduction of CBIR and Q-Synth are, respectively, 12.17% and 16.63% at most and 6.45% and -0.53% on average on the same benchmarks.