  Photonic platforms represent a promising technology for the realization of
several quantum communication protocols and for experiments of quantum
simulation. Moreover, large-scale integrated interferometers have recently
gained a relevant role for restricted models of quantum computing, specifically
with Boson Sampling devices. Indeed, various linear optical schemes have been
proposed for the implementation of unitary transformations, each one suitable
for a specific task. Notwithstanding, so far a comprehensive analysis of the
state of the art under broader and realistic conditions is still lacking. In
the present work we address this gap, providing in a unified framework a
quantitative comparison of the three main photonic architectures, namely the
ones with triangular and square designs and the so-called fast transformations.
All layouts have been analyzed in presence of losses and imperfect control over
the reflectivities and phases of the inner structure. Our results represent a
further step ahead towards the implementation of quantum information protocols
on large-scale integrated photonic devices.
