title: Two-photon coincident-frequency entanglement via extended phase matching.
abstract: 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.
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Onur
authors.initials: O
authors.lastname: Kuzucu
authors.forename: Marco
authors.initials: M
authors.lastname: Fiorentino
authors.forename: Marius A
authors.initials: MA
authors.lastname: Albota
authors.forename: Franco N C
authors.initials: FN
authors.lastname: Wong
authors.forename: Franz X
authors.initials: FX
authors.lastname: Kärtner