Squeezing in Fourth-Order Parametric Downconversion

John Rarity, P. R. Tapster

John G. Rarity, P. R. Tapster

A two-photon state can be selected by coincidence detection of photon pairs created in parametric downconversion. We demonstrate a reduction in the coincidence-count rate when pairs of photons are combined in a beam splitter. This reduction occurs only when photon wave functions overlap and can permit accurate (subpicosecond) relative timing measurements. We relate the width of the coincidence reduction to the bandwidth of the downconverted light and thence to the detailed phase-matching conditions in the parametric downconversion crystal. We also demonstrate that the loss of coincidences is associated with an increased probability of detection of photon pairs in each output of the beam splitter.

Faisal A. A. El-Orany, M. Sebawe Abdalla, Jan Peřina

Ayman F. Abouraddy, Bahaa E. A. Saleh, Alexander V. Sergienko +1 more

In this paper we investigate the fourth-order coherence of biphoton beams from spontaneous parametric downconversion resulting from a nonlinear crystal as exemplified in a double-slit interference configuration where the signal and idler beams both pass through the same double slits. We find that the angle of the crystal optical axis and the crystal length are important factors, along with the double-slit separation and system bandwidth, in determining the nature of the fourth-order interference pattern obtained behind the slits. Only careful planning of system parameters and understanding of the tuning curves of the downconversion will illuminate the obtained coincidence patterns.

Dmitri S. Mogilevtsev

Z. Y. Ou, Harry J. Kimble

With regard to the system of parametric downconversion, we analyze a recently proposed experiment for demonstrating the nonlocal property of a single photon.1 In the original proposal by Tan et al., a light field in a single photon-number state is split into two beams, which are then homodyned with two spatially separated weak local oscillators. The two-photon detection probability with the two homodyned beams provides evidence for nonlocality. It is shown that this phenomenon is in essence a phase-sensitive fourth-order interference effect. A single photonnumber state can be achieved from the pair of photons produced in parametric downconversion processes.2 A multimode model for the downconversion process is used to carry out the calculation of three-photon detection probability that is associated with nonlocality of a single photon.