Realistic simulation of universal multiport interferometers with losses within a Gaussian formalism

Abstract

Photonic technologies are among the leading platform contenders for demonstrating quantum advantage. Nevertheless, photon losses represent the major hurdle for the realization of a fault-tolerant optical quantum computer, and the need for an accurate characterization of this phenomenon is crucial for classical simulations of quantum algorithms on noisy backends. The noisy regime would require the simulation of the algorithm on a Fock backend or rather assuming the a priori hypothesis on the uniformity of the optical losses, which may lead to wrong predictions about the outcome from the algorithm on a cerain hardware. We propose a Gaussian model that can reproduce a lossy dynamics through the experimental characterization of imperfect interferometers, yielding the corresponding mean vector and the covariance matrix. Such model can be adapted to any continuous-variable architecture (spatial or time-bin encoded) and for both the Gaussian boson sampling or general-dyne based algorithms. Eventually, we quantify the drift of optical losses from being uniform throughout the multiport interferometer by a numerical simulation. This work proposes a blueprint for future characterizations, tailor-suited for specific devices and architectures, as well as for potential error correction and mitigation techniques, and it paves the way for realistic simulations of quantum algorithms on NISQ optical platforms.