Bright phase-stable broadband fiber-based source of polarization-entangled photon pairs

Abstract

We describe an achromatic, phase-stable, broadband source of polarization-entangled photon pairs with high spectral brightness that uses four-wave mixing in a fiber Sagnac interferometer. We achieved a polarization-entangled two-photon coincidence rate of $7\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}$ per $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{THz}$ $(0.9\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$ of bandwidth per $300\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{W}$ of average pump power. At this rate, we observed two-photon fringe interference visibilities greater than 97%, over a $10\phantom{\rule{0.3em}{0ex}}\mathrm{THz}$ $(\ensuremath{\approx}21\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$ spectral range. We measured violations of Bell's inequality by more than 22 standard deviations for each of the four Bell states in less than $3\phantom{\rule{0.3em}{0ex}}\text{minutes}$ per state. The high spectral brightness $(26\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}\phantom{\rule{0.2em}{0ex}}{\mathrm{nm}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{mW}}^{\ensuremath{-}1})$, large tunable wavelength range, single spatial mode, and phase stability make this source a promising candidate for a wide range of quantum-information applications.