Spatially Separated Two Color Photons in Fourth Order Interference

J. G. Rarity, P. R. Tapster

Angle-separated pair photons emitted in spontaneous parametric fluorescence are superimposed at a beamsplitter and detected by coincidence techniques. The coincidence disappears when the photon path lengths to the beamsplitter are equal to within their inverse bandwidth due to fourth-order interference. The photon bandwidth is set by wide apertures placed to satisfy phase-matching conditions at the nonlinear crystal. The resulting broadband photons are short (39-fs full width at half maximum) and show an oscillatory tail resulting from the hard-edge apertures. Two-color photons are created by blocking the central portion of the apertures leading to strong oscillations of the coincidence rate as a function of path-length difference. Both effects are predicted by the theory of fourth-order interference coupled with the detailed phase-matching conditions in the nonlinear crystal used as a source. The two colors overlap at different positions on the beamsplitter. We show how this could be used as a test of local realistic theories by formulating a Bell inequality based on relative phases between the colors.

John G. Rarity, P. R. Tapster

M. G. Raymer, S. J. van Enk, Colin J. McKinstrie +1 more

John Rarity, P. R. Tapster

Two-color photon pairs are selected by two double apertures placed to satisfy the phase-matching conditions at a down-conversion crystal. The different wavelengths are superposed at spatially separated points on a beamsplitter and coincident two-photon detections are measured. On adjusting phase plates in the beams before the beamsplitter an apparent nonlocal fourth-order interference effect is seen which violates Bell's inequality by several standard deviations.

江国进 Jiang Guojin, 陈平形 Chen Pingxing, 李承祖 Li Chengzu

Timothy M. Yarnall, Ayman F. Abouraddy, Bahaa E. A. Saleh +1 more

We report the results of two experiments performed with two-photon light, produced via collinear degenerate optical spontaneous parametric downconversion (SPDC), in which both second-order (one-photon) and fourth-order (two-photon) interferograms are recorded in a Mach-Zehnder interferometer (MZI). In the first experiment, high-visibility fringes are obtained for both the second- and fourth-order interferograms. In the second experiment, the MZI is modified by the removal of a mirror from one of its arms; this leaves the fourth-order interferogram unchanged, but extinguishes the second-order interferogram. A theoretical model that takes into consideration both the temporal and spatial degrees-of-freedom of the two-photon state successfully explains the results. While the temporal interference in the MZI is independent of the spatial coherence of the source, that of the modified MZI is not.