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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Observation of nontrivial correlation and anti-correlation from pulsed chaotic-thermal light

Sanjit Karmakar, Zhenda Xie, Hui Chen, Yanhua H. Shih

Published Aug 20, 2009• 0 citations
Publisher

Abstract

We have observed a nontrivial spatial correlation and anti-correlation from a ∼200 femtosecond pulsed chaoticthermal source. The classical picture of statistical correlation of intensity fluctuations fails to give an adequate interpretation. In the view of quantum mechanics these observations are the result of two-photon interference, involving the superposition of two-photon amplitudes, nonclassical entities corresponding to different yet indistinguishable alternative ways of triggering a joint-detection event.

DOI
10.1117/12.828406

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We have observed a nontrivial spatial correlation and anti-correlation from a ∼200 femtosecond pulsed chaoticthermal source. The classical picture of statistical correlation of intensity fluctuations fails to give an adequate interpretation. In the view of quantum mechanics these observations are the result of two-photon interference, involving the superposition of two-photon amplitudes, nonclassical entities corresponding to different yet indistinguishable alternative ways of triggering a joint-detection event.
We wish to report an experimental observation of anti-correlation from first-order incoherent classical chaotic light. We explain why the classical statistical theory does not apply and provide a quantum interpretation. In quantum theory, either correlation or anti-correlation is a two-photon interference phenomenon, which involves the superposition of two-photon amplitudes, a nonclassical entity corresponding to different yet indistinguishable alternative ways of producing a joint-photodetection event.
Two-photon correlation phenomena, including the historical experiment of Hanbury Brown and Twiss, may have to be described quantum mechanically, regardless of whether the source of radiation is classical or quantum. Supporting this point, we present a ghost imaging type of second-order spatial correlation experiment of chaotic light to show that the classical understanding based on the concept of statistical intensity fluctuations does not give a correct interpretation for the observation. From a practical point of view, this experiment demonstrates the possibility of having high contrast lensless two-photon imaging with chaotic light, suggesting imaging applications for radiations for which no effective lens is available.
One of the most surprising consequences of quantum mechanics is the nonlocal behavior of a multi-particle system. Although questions regarding fundamental issues of quantum theory still exist, nonclassical surprises have started to play important roles in practical applications. Ghost imaging is one of these exciting areas. Two types of ghost imaging have been experimentally demonstrated since 1995. Type-one ghost imaging uses entangled photon pairs and type-two ghost imaging uses chaotic light. The unique point-to-point image-forming correlation between the object and image planes in ghost imaging is the result of a constructive-destructive interference which involves the nonlocal superposition of two-photon amplitudes, a nonclassical entity corresponding to different yet indistinguishable alternative ways of triggering a joint-detection event. This talk will explore and analyze the quantum nature of ghost imaging. It is true that classical challenges have never stopped. Quantum? Classical? A hot debate is currently focused on ghost imaging. This talk will defend the quantum mechanical point of view.
The study of entangled states greatly advanced our understanding about two-photon interferometry. Two-photon interference is not the interference between two photons, it is about a pair of photons interfering with the pair itself. In the language of quantum theory, two-photon interference is the result of superposition between different yet indistinguishable two-photon probability amplitudes. Under certain conditions, the observed second-order interference can be factorized into a product of two individual classic first-order interferences. In this case, the interference is not only observable from the intensity fluctuation correlation measurement, or from the photon number fluctuation correlation measurement, of two photodetectors, but also observable in the counting rate of each individual photodetector. It may not be uneasy to accept the quantum concept of two-photon interference for “classical” thermal radiation. Indeed, the radiation Planck dealt with was “classical” thermal light. Perhaps, no one would even expect observing nontrivial second-order correlation from a laser beam, since laser field is non-Gaussin.
Indistinguishability of events in quantum mechanics is manifested by interference between their probability amplitudes. We report a unique kind of interference occurring between indistinguishable events of photon-pair emission, where each photon of the pair is emitted from a distinct true chaotic light source and has a different energy. The indistinguishability results in an interference which is observed as an ultrafast modulation of the second-order coherence function, measured on a femtosecond time scale by two-photon absorption in a semiconductor photomultiplier tube.