  Photon number resolving detectors are the ultimate measurement of quantum
optics, which is the reason why developing the technology is getting
significant attention in recent years. With this arises the question of how to
evaluate the performance of the detectors. We suggest that performance of a
photon number detector can be evaluated by comparing it to a multiplex of
on-off detectors in a practical scenario: conditional preparation of a photon
number state. Here, both the quality of the prepared state and the probability
of the preparation are limited by the number of on-off detectors in the
multiplex, which allows us to set benchmarks that can be achieved or surpassed
by the photon number resolving detectors.
