title: A wavelength-tunable fiber-coupled source of narrowband entangled photons.
abstract: We demonstrate a wavelength-tunable, fiber-coupled source of polarization- entangled photons with extremely high spectral brightness and quality of entanglement. Using a 25 mm PPKTP crystal inside a polarization Sagnac interferometer we detect a spectral brightness of 273000 pairs (s mW nm)(-1), a factor of 28 better than comparable previous sources while state tomography showed the two-photon state to have a tangle of T = 0.987. This improvement was achieved by use of a long crystal, careful selection of focusing parameters and single-mode fiber coupling. We demonstrate that, due to the particular geometry of the setup, the signal and idler wavelengths can be tuned over a wide range without loss of entanglement.
authors: Alessandro
authors: A
authors: Fedrizzi
authors: Thomas
authors: T
authors: Herbst
authors: Andreas
authors: A
authors: Poppe
authors: Thomas
authors: T
authors: Jennewein
authors: Anton
authors: A
authors: Zeilinger