We introduce a filter using a noise-free quantum buffer with large optical bandwidth that can both filter temporal-spectral modes, as well as inter-convert them and change their frequency. We show that such quantum buffers optimally filter out temporal-spectral noise; producing identical single-photons from many distinguishable noisy single-photon sources with the minimum required reduction in brightness. We then experimentally demonstrate a noise-free quantum buffer in a warm atomic system that is well matched to quantum dots and can outperform all intensity (incoherent) filtering schemes for increasing indistinguishability.
@article{arxiv.1902.07720,
title = {Optimal Coherent Filtering for Single Noisy Photons},
author = {S. Gao and O. Lazo-Arjona and B. Brecht and K. T. Kaczmarek and S. E. Thomas and J. Nunn and P. M. Ledingham and D. J. Saunders and I. A. Walmsley},
journal= {arXiv preprint arXiv:1902.07720},
year = {2019}
}