Quantifying n -Photon Indistinguishability with a Cyclic Integrated Interferometer
Résumé
We report on a universal method to measure the genuine indistinguishability of
n
photons—a crucial parameter that determines the accuracy of optical quantum computing. Our approach relies on a low-depth cyclic multiport interferometer with
N
=
2
n
modes, leading to a quantum interference fringe whose visibility is a direct measurement of the genuine
n
-photon indistinguishability. We experimentally demonstrate this technique for an eight-mode integrated interferometer fabricated using femtosecond laser micromachining and four photons from a quantum dot single-photon source. We measure a four-photon indistinguishability up to
0.81
±
0.03
. This value decreases as we intentionally alter the photon pairwise indistinguishability. The low-depth and low-loss multiport interferometer design provides an original path to evaluate the genuine indistinguishability of resource states of increasing photon number.