Experimental characterization of the spatial fluctuations of parametric fluorescence and of a coherent beam

S. T. Gevorkyan, G. Yu. Kryuchkov

Antonio Picozzi, Marc Haelterman

We consider the basic problem of spontaneous parametric generation from quantum noise fluctuations in the presence of a continuous plane-wave pump. We show, both numerically and analytically, that the walk-off between the down-converted fields is the key ingredient that leads to the generation of coherent fields in the parametric process. Along these lines, our theory reveals that, in the absence of walk-off, diffraction and chromatic dispersion in usual quadratically nonlinear materials only lead to incoherent erratic dynamics. Moreover, a two-dimensional study shows that, when the walk-off is exclusively temporal (or spatial), the parametric process is not able to yield the generation of spatially (or temporally) coherent fields. This study sheds light on the problem of coherence in parametric fluorescence and, in particular, allows us to explain various recent experimental observations.

Antonio Picozzi, Marc Haelterman

Summary form only given. We consider the basic problem of spontaneous parametric generation from quantum noise fluctuations. Various experiments revealed that in the parametric fluorescence process a transition occurs between two regimes respectively characterized by the incoherence of the initial quantum noise and the coherence of the generated signal and idler fields. We investigate the mechanism responsible for the incoherence-to-coherence transition.

Martin Hamar, Jan Peřina, Václav Michálek +1 more

周南 Zhou Nan, 李大伟 Li Dawei, 崔勇 Cui Yong +2 more

Jean‐François Morizur

We present in this thesis a study of the spatial properties of light at the quantum level. More specifically, we focus on techniques to manipulate the quantum fluctuations of different degrees of freedom in a beam's transverse plane, and on the quantum protocols we can implement using these specific fluctuations. We begin by providing an experimental characterization of different methods to manipulate the quantum fluctuations of multiple transverse profiles, or modes, in one beam. While manipulating the quantum fluctuations of a mode, a process known as squeezing, for a single mode beam can be performed very efficiently using a conventional optical parametric oscillator, we present implementations of different, less conventional techniques able to generate a beam carrying multiple squeezed modes. Conventionally, the squeezed modes we can generate using these techniques are fixed by the optical design. We present a new optical system, called a Unitary Programmable Mode Converter (UPMC), able to reshape these modes at will. We show theoretically that such a UPMC can in principle perform any desired reshaping of the modes. We present the performances of an experimental implementation of the UPMC, both in a classical and quantum context. We find that the UPMC performs as predicted, and we present a method to optimize the UPMC settings taking into account experimental restrictions. The UPMC, combined with a technique to build a beam carrying multiple squeezed modes, allows us to generate a beam with squeezing in any desired set of spatial modes. In order to detect these fluctuations, we built a multipixel homodyne detection, a detection system able to record simultaneously the quantum fluctuations in all these modes. We provide in this thesis our solutions to overcome the electronic challenges associated with such a device, and present an experimental characterization of the performances of our multipixel homodyne detection. Finally, we combine these experimental characterizations to discuss how these techniques help us implement different quantum protocols involving multiple spatial modes, more specifically quantum enhanced detections and cluster states quantum computation.