Photon indistinguishability plays a fundamental role in information processing, with applications such as linear-optical quantum computation and metrology. It is then necessary to develop appropriate tools to quantify the amount of this resource in a multiparticle scenario. Here we report a four-photon experiment in a linear-optical interferometer designed to simultaneously estimate the degree of indistinguishability between three pairs of photons. The interferometer design dispenses with the need of heralding for parametric down-conversion sources, resulting in an efficient and reliable optical scheme. We then use a recently proposed theoretical framework to quantify genuine four-photon indistinguishability, as well as to obtain bounds on three unmeasured two-photon overlaps. Our findings are in high agreement with the theory, and represent a new resource-effective technique for the characterization of multiphoton interference.
@article{arxiv.1907.01325,
title = {Experimental quantification of genuine four-photon indistinguishability},
author = {Taira Giordani and Daniel J. Brod and Chiara Esposito and Niko Viggianiello and Marco Romano and Fulvio Flamini and Gonzalo Carvacho and Nicolò Spagnolo and Ernesto F. Galvão and Fabio Sciarrino},
journal= {arXiv preprint arXiv:1907.01325},
year = {2020}
}