Abstract: I will describe the realization of a high spectral brightness, broad wavelength coverage, single-spatial mode source of polarization-entangled photon pairs operated at room temperature. The source takes advantage of single-mode fiber optics, large two-photon production probability via four-wave mixing in a nonlinear microstructure fiber, low single-photon noise level, and the inherent stability provided by a Sagnac interferometer. With a modest average pump power (300 uW), we created all four Bell states with a detected two-photon coincidence rate of 7 kHz per bandwidth of 0.9 nm over a spectral range of more than 20 nm [PRA 76, 043836 (2007)]. We performed quantum-state tomography to reconstruct the density matrices of the states, with the fidelity of each Bell state measuring 95% or more [Opt. Express 15, 18339 (2007)]. In addition to being useful for quantum-information applications, this high-fidelity source of entangled photons can also be used for fundamental tests of quantum mechanics. Using polarization-entangled two-photon singlet states, we compared our measurements of two-photon polarization correlations to the predictions of quantum mechanics, and also to the predictions of certain local realistic and non-local realistic theories. Our measurements were consistent with quantum-mechanical predictions, resulting in a violation of Bell's inequality in the Clauser-Horne-Shimony-Holt form by 15 standard deviations (excluding local hidden-variable theories) and a violation of a Leggett-type non-local hidden-variable inequality by 3 standard deviations (excluding a certain class of non-local hidden-variable theories) [PRA 77, 032339 (2008)]. |
