  Photonic processors are pivotal for both quantum and classical information
processing tasks using light. In particular, linear optical quantum information
processing requires both largescale and low-loss programmable photonic
processors. In this paper, we report the demonstration of the largest universal
quantum photonic processor to date: a low-loss, 12-mode fully tunable linear
interferometer with all-to-all coupling based on stoichiometric silicon nitride
waveguides.
