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

Abstract: 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. The devised optimizer effectively captures the intrinsic patterns of the QCT circuits, and the experimental results demonstrate that our algorithm can significantly reduce the depth of QCT circuits, 26.68\% at most and 12.18\% on average, across all benchmark circuits.