title: Joint temporal density measurements for two-photon state characterization.
abstract: We demonstrate a technique for characterizing two-photon quantum states based on joint temporal correlation measurements using time-resolved single-photon detection by femtosecond up-conversion. We measure for the first time the joint temporal density of a two-photon entangled state, showing clearly the time anticorrelation of the coincident-frequency entangled photon pair generated by ultrafast spontaneous parametric down-conversion under extended phase-matching conditions. The new technique enables us to manipulate the frequency entanglement by varying the down-conversion pump bandwidth to produce a nearly unentangled two-photon state that is expected to yield a heralded single-photon state with a purity of 0.88. The time-domain correlation technique complements existing frequency-domain measurement methods for a more complete characterization of photonic entanglement.
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Onur
authors.initials: O
authors.lastname: Kuzucu
authors.forename: Franco N C
authors.initials: FN
authors.lastname: Wong
authors.forename: Sunao
authors.initials: S
authors.lastname: Kurimura
authors.forename: Sergey
authors.initials: S
authors.lastname: Tovstonog