In a recent Letter [Phys. Rev. Lett. 118, 030501 (2017)], Peiris, Konthasinghe, and Muller report a Franson interferometry experiment using pairs of photons generated from a two-level semiconductor quantum dot. The authors report a visibility of 66% and claim that this visibility "goes beyond the classical limit of 50% and approaches the limit of violation of Bell's inequalities (70.7%)." We explain why we do not agree with this last statement and how to fix the problem.
@article{arxiv.1703.05055,
title = {Comment on "Franson Interference Generated by a Two-Level System"},
author = {Jonathan Jogenfors and Adán Cabello and Jan-Åke Larsson},
journal= {arXiv preprint arXiv:1703.05055},
year = {2017}
}