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Observation of a spatial quantum correlation in parametric down conversion

Parametric down conversion produces twin photons which are temporally and spatially perfectly correlated at the quantum level. This effect has been extensively used at the photon counting level in beautiful and famous experiments.

When the pump intensity is raised by a large factor, with the help of intense pulsed lasers, many twin photons are produced, which cannot be counted individually. One obtains on the signal and idler beams quantum correlated images, each having large pixel to pixel fluctuations, but with (almost) identical intensity values in a single shot on the symmetrical pixels of the signal and idler images.

In the high parametric gain regime where roughly 10 to 100 photons were recorded on average on each pixel, the INFM experimental group succeeded in demonstrating such a pixel to pixel quantum correlation in a single shot spatial statistics.

The best spatial noise reduction was about 50% below the standard quantum limit. This important achievement can now be used to information processing

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Universita' dell'Insubria
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