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Conference on Lasers and Electro-Optics

Spatial coherence of light in the two-photon state

E. J. S. Fonseca, Carlos Henrique Monken, N. Padua, G.A. Barbosa

Published Nov 27, 2002• 0 citations
Publisher

Abstract

Summary form only given. We present experimental results of the Young's double-slit interference pattern of light in the two-photon state. By doing Young's interference experiments with the output light of a Hong-Ou-Mandel (H-O-M) interferometer, we are able to study the spatial coherence properties of the light in the two photon state (two photons in the same wave packet).

DOI
10.1109/iqec.1998.680281

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Summary form only given. We present experimental results of the Young's double-slit interference pattern of light in the two-photon state. By doing Young's interference experiments with the output light of a Hong-Ou-Mandel (H-O-M) interferometer, we are able to study the spatial coherence properties of the light in the two photon state (two photons in the same wave packet).
Measurements of the Young interference pattern for down-converted light in the two-photon state are performed. Light in the two-photon state is generated at the output of a Hong-Ou-Mandel balanced interferometer. Two-photon interference patterns with visibilities up to 100% are obtained. Visibilities of the two-photon interference patterns as a function of the double-slit separation are obtained and show that the transverse coherence length of the two-photon light is much larger than the one-photon beam for the distances considered in the experiment.
This article reports a study on a turbulence-free Young's double-slit interferometer. When the environmental turbulence blurs out the classic Young's double-slit interference completely, a two-photon interference pattern is still observable from the measurement of intensity or photon number fluctuation correlation. This two-photon interferometer always produces a turbulence-free interference pattern, when the double-slit interferometer is utilizing both first-order spatially incoherent light and spatially coherent light. This type of two-photon interferometer establishes new capabilities in optical observations and sensing measurements that require high sensitivity and stability.
In classical optics, Young's double-slit experiment with colored coherent light gives rise to individual interference fringes for each light frequency, referring to single-photon interference. However, two-photon double-slit interference has been widely studied only for wavelength-degenerate biphoton, known as subwavelength quantum lithography. In this work, we report double-slit interference experiments with two-color biphoton. Different from the degenerate case, the experimental results depend on the measurement methods. From a two-axis coincidence measurement pattern we can extract complete interference information about two colors. The conceptual model provides an intuitional picture of the in-phase and out-of-phase photon correlations and a complete quantum understanding about the which-path information of two colored photons.
An understanding of the phenomenon of light interference forms the kernel underlying the discovery of the nature of light from the viewpoints of both classical physics and quantum physics. Here we report on two-photon interference with temporally separated continuous-wave coherent photons by using a temporal post-selection method with an arbitrary time delay. Although the temporal separation of a day between the photons is considerably longer than the coherence time of the light source, we observe the Hong–Ou–Mandel (HOM) interference of the pairwise two-photon state. Furthermore, we experimentally demonstrate the HOM interference observed in one of the interferometer-output modes by using only one single-photon detector for a large temporal separation.
The spatial second-order interference of two independent pseudothermal light beams in a Hong-Ou-Mandel interferometer is studied experimentally and theoretically. The similar cosine modulation in the second-order coherence function as the one with entangled-photon pairs in a Hong-Ou-Mandel interferometer is observed. Two-photon interference based on Feynman's path integral theory is employed to interpret the results. The experimental results and theoretical simulations agree with each other very well.
For centuries Young’s double-slit interference continues to be a hot discussion subject about whether light is waves or particles. This work unravels the self-interference parados, and sheds light on such a concept that assumes a photon can split, self-interfere, and recombine. This work elucidates how coherent photons from a laser source could produce a double-slit interference pattern without the hypothesis of unphysical splitting and recombination of a single photon. Unlike the conventional single wave-function description for the whole ensemble of particles, we develop a pilot-wave trajectory approach to track every photon’s wave-packet propagation and calculate the evolution of the interference intensity in time. We demonstrate how wave packets and phase coherence affect the interference pattern. To resolve the century-old self-interference paradox, we show that such an hypothesis is unnecessary, and the illusion is due to the long coherence length of laser photons and overlaps of delocalized light wave packets.