طرح‌واره‌هاي نظري براي آشكارسازي سرشت كوانتومي امواج گرانشي اوليه از طريق رديابي ويژگي‌هاي كوانتومي امواج الكترومغناطيسي

One of the fundamental outcomes of inflationary cosmology is that tensorial perturbations of spacetime, similar to the large-scale structure of our Universe, originate from quantum fluctuations during the inflationary epoch. Creation an‎d amplification of inflationary- generated primordial gravitational waves lie in the middle of the crossroad where quantum mechanics meet cosmology. Thus, detecting their quantumness, especially their squeezed nature, not only paves the way to search for the quantum essence of gravitational waves but also may provide a hitherto inaccessible source of information about the early Uni- verse. In this dissertation, we present a comprehensive investigation of the interaction be- tween quantum gravitational waves an‎d electromagnetic fields that are supposed to probe quantum spacetime. Using the optical medium analogy framework, we not only recover the usual results of a typical interferometer detector in terms of the phase shift, but we may also promote the investigation to a fully quantum mechanical one, where the appli- cation of the well-known quantum optical language in analog systems, helps understan‎d the electromagnetic-gravitational wave interaction in a close-up. In particular, we assess the quadrature variance of the electromagnetic field an‎d demonstrate the impossibility of witnessing the quantum nature of gravitational waves based on the revivals of optical squeezing. On the contrary, we show that primordial gravitational waves induce decoher- ence of the electromagnetic field an‎d ruin temporal correlations after a characteristic time scale, which depends on the cosmological parameters, namely the inflationary index an‎d the tensor-to-scalar ratio. Moreover, the apparition of sideban‎ds in the optical spectrum may be viewed as a signature of the squeezed nature of relic gravitational waves. More- over, we investigate the effect of quantum background of GWs on the phase correlations of EM field emitted from distant sources. We show that primordial gravitational waves placed in two-mode squeezed state could ruin van Citter-Zernike correlations, an effect called as the blurring of the visibility. Although the effect crucially depends on the value of tensor-to-scalar ratio, it turns out that for the current upper-bounds on this parameter, the incoherence effect is too feeble that can not ruin electromagnetic phase correlations. Nevertheless, we promote the idea of using spatial correlations of light as a new tool to explore the primordial gravitational background.

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Alain Blanchard ,Brahim Lamine