We demonstrate a new class of frequency-entangled states generated via spontaneous parametric down-conversion under extended phase matching conditions. Biphoton entanglement with coincident signal and idler frequencies is observed over a broad bandwidth in periodically poled KTiOPO4. We demonstrate high visibility in Hong-Ou-Mandel interferometric measurements under pulsed pumping without spectral filtering, which indicates excellent frequency indistinguishability between the down-converted photons. The coincident-frequency entanglement source is useful for quantum information processing and quantum measurement applications.
@article{arxiv.quant-ph/0410216,
title = {Two-photon coincident-frequency-entanglement via extended phase matching},
author = {Onur Kuzucu and Marco Fiorentino and Marius A. Albota and Franco N. C. Wong and Franz X. Kaertner},
journal= {arXiv preprint arXiv:quant-ph/0410216},
year = {2009}
}