Why Biphoton But Not Two Photons

Yanhua H. Shih, Dmitry Strekalov, T. D. Pittman

Ravyn Malatesta, Jiho Noh, Tomás Santiago‐Cruz +6 more

Two-photon interference between two photon pairs, or biphotons, requires the interfering biphotons to be indistinguishable. Previously, researchers have demonstrated this by coherently pumping two identical but separate nonlinear materials or using multipass interferometric setups. In contrast, we demonstrate two-photon interference of biphotons simultaneously emitted by two overlapping resonances in the same nonlinear source—a nonlinear metasurface.

Magued B. Nasr, Ayman F. Abouraddy, Mark C. Booth +5 more

We study two-photon excitation using biphotons generated via the process of spontaneous parametric down conversion in a nonlinear crystal. We show that the focusing of these biphotons yields an excitation distribution that is the same as the distribution of one-photon excitation at the pump wavelength. We also demonstrate that biphoton excitation in the image region yields a distribution whose axial width is approximately that of the crystal thickness and whose transverse width is that of the pump at the input to the crystal.

Shengwang Du, Rubin, Morton H., Wen, Jianming

Maria V. Chekhova, O. A. Shumilkina

A method for generating two-photon wave packets (biphotons) with a small width of the spatial intensity correlation function (correlation radius) has been considered. We propose to prepare a two-photon wave packet inhomogeneously broadened in the angle by means of spontaneous parametric down-conversion in an inhomogeneous crystal. Such biphotons are not diffraction limited; i.e., their correlation radius is much larger than the inverse width of the spatial spectrum. However, the correlation radius of such a biphoton decreases as the biphoton propagates in free space, and transverse compression occurs at a certain distance from the crystal; i.e., the biphoton becomes diffraction limited.