Parameter-Shift Rules Cut Boson Sampling Gradient Calculations

Researchers have derived higher order parameter-shift rules for calculating gradients in boson sampling experiments, a development addressing a persistent challenge in photonic quantum computing: photon loss within interferometers. While parameter-shift rules generally do not apply to Gaussian boson sampling, the team demonstrated they are possible when an interferometer’s transmission matrix is structured as a diagonal loss matrix multiplied by a pure unitary. This specific factorization allows for parameter-shift rules with an order defined by twice the total number of photons detected. The researchers validated their method using real hardware, achieving performance comparable to…