We characterize operationally meaningful quantum gains in a paradigmatic model of lossless multiple-phase interferometry and stress insufficiency of the analysis based solely on the concept of quantum Fisher information. We show that the advantage of the optimal simultaneous estimation scheme amounts to a constant factor improvement when compared with schemes where each phase is estimated separately -- contrary to a widely cited results claiming a better precision scaling in terms of the number of phases involved.
@article{arxiv.2107.10863,
title = {Multiple-phase quantum interferometry -- real and apparent gains of measuring all the phases simultaneously},
author = {Wojciech Gorecki and Rafal Demkowicz-Dobrzanski},
journal= {arXiv preprint arXiv:2107.10863},
year = {2022}
}