title: Optimizing type-I polarization-entangled photons.
abstract: Optical quantum information processing needs ultra-bright sources of entangled photons, especially from synchronizable femtosecond lasers and low-cost cw-diode lasers. Decoherence due to timing information and spatial mode-dependent phase has traditionally limited the brightness of such sources. We report on a variety of methods to optimize type-I polarization-entangled sources--the combined use of different compensation techniques to engineer high-fidelity pulsed and cw-diode laser-pumped sources, as well as the first production of polarization-entanglement directly from the highly nonlinear biaxial crystal BiB(3)O(6) (BiBO). Using spatial compensation, we show more than a 400-fold improvement in the phase flatness, which otherwise limits efficient collection of entangled photons from BiBO, and report the highest fidelity to date (99%) of any ultrafast polarization-entanglement source. Our numerical code, available on our website, can design optimal compensation crystals and simulate entanglement from a variety of type-I phasematched nonlinear crystals.
authors.affiliation: Department of Physics, University of Illinois, 1110 Green Street, Urbana, IL 61801, USA. rangaraj@illinois.edu
authors.forename: Radhika
authors.initials: R
authors.lastname: Rangarajan
authors.forename: Michael
authors.initials: M
authors.lastname: Goggin
authors.forename: Paul
authors.initials: P
authors.lastname: Kwiat