Noise reduction of multimode Gaussian-boson-sampling circuits via unitary averaging

We improve Gaussian-boson-sampling circuits by integrating the unitary-averaging (UA) protocol, previously demonstrated to protect unknown Gaussian states from phase errors [Swain et al., Phys. Rev. A 110, 032622 (2024)]. Our work extends the applicability of UA to mitigate arbitrary interferometric noise, including beam-splitter and phase-shifter imperfections. Through comprehensive numerical analysis, we demonstrate that UA consistently achieves higher fidelity and success probability than unprotected circuits, establishing its robustness in noisy conditions. Remarkably, enhancement is maintained across varying numbers of modes with respect to the noise. We further derive a power-law formula predicting performance gains in large-scale systems, including 100-mode and 216-mode configurations. A detailed step-by-step algorithm for implementing the UA protocol is also provided, offering a practical road map for advancing near-term quantum technologies.