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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Quantum limits in image processing

V. Delaubert, Nicolas Treps, Claude Fabre, Hans‐A. Bachor, Philippe Réfrégier

Published Jun 1, 2007• 1 citation
Publisher

Abstract

In order to accurately describe optical images, the quantum nature of light must be taken into account, even when the image is formed of a great number of photons. On the one hand, the inevitable quantum fluctuations of light degrade the quality of the image, but on the other hand, the possibility of creating strong quantum correlations or even entanglement between the different points open new possibilities for improving information extraction and read-out from the image.

DOI
10.1109/cleoe-iqec.2007.4386912

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In order to accurately describe optical images, the quantum nature of light must be taken into account, even when the image is formed of a great number of photons. On the one hand, the inevitable quantum fluctuations of light degrade the quality of the image, but on the other hand, the possibility of creating strong quantum correlations or even entanglement between the different points open new possibilities for improving information extraction and read-out from the image.
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Abstract In previous years the possibility of creating and manipulating quantum states of light has paved the way for the development of new technologies exploiting peculiar properties of quantum states, such as quantum information, quantum metrology and sensing, quantum imaging, etc. In particular quantum imaging addresses the possibility of overcoming limits of classical optics by using quantum resources such as entanglement or sub-Poissonian statistics. Albeit, quantum imaging is a more recent field than other quantum technologies, e.g. quantum information, it is now mature enough for application. Several different protocols have been proposed, some of them only theoretically, others with an experimental implementation and a few of them pointing to a clear application. Here we present a few of the most mature protocols ranging from ghost imaging to sub shot noise imaging and sub-Rayleigh imaging.
Since Hanbury Brown and Twiss revealed the photon bunching effect of a thermal light source in 1956, almost all studies in correlation optics have been based on light’s intensity fluctuation, regardless of fact that the polarization fluctuation is a basic attribute of natural light. In this work, we uncover the veil of the polarization fluctuation and corresponding photon correlations by proposing a new light source model, termed pseudo-natural light, embodying both intensity and polarization fluctuations. Unexpectedly, the strong antibunching and superbunching effects can be simultaneously realized in such a new source, whose second-order correlation coefficient g ( 2 ) can be continuously modulated across 1. For the symmetric Bernoulli distribution of the polarization fluctuation, particularly, g ( 2 ) can be in principle from 0 to unlimitedly large. In pseudo-natural light, while the bunching effects of both intensity and polarization fluctuations enhance the bunching to superbunching photon correlation, the antibunching correlation of the polarization fluctuation can also be extracted through the procedure of division operation in the experiment. The antibunching effect and the combination with the bunching one will arouse new applications in quantum imaging. As heuristic examples, we carry out high-quality positive or negative ghost imaging, and devise high-efficiency polarization-sensitive and edge-enhanced imaging. This work, therefore, sheds light on the development of multiple and broad correlation functions for natural light.
Ghost imaging allows one to obtain information on an object from the spatial correlation function between photons propagating through or reflected from the object and photons of the reference arm. In this case, detection in the object arm is performed over the entire aperture of the beam and, therefore, it does not give information on the object. The reference beam does not interact with the object, but is recorded with a scanning point detector or a CCD array permitting the measurement of the spatial correlation function of photons in two arms. The use of multimode entangled quantum light beams by illuminating the object by one beam and orienting other beams to reference arms makes it possible to obtain simultaneously several ghost images (GIs). Cross correlations of multiplexed GIs (MGIs) are determined by eighth-order field correlation functions. A special algorithm is developed for calculating higher-order correlations of Bose operators. The presence of GI cross correlations is used for improving the quality of the reconstructed object’s image by their processing using the measurement reduction method. An example of the computer simulation of the image reconstruction by MGIs formed in the field of four-frequency entangled quantum states is considered. It is found that in this case the reduced GI has a signal-to-noise ratio several times higher than that of GIs.