Thesis of Shivange Srivastava

Defense of thesis of Shivange Srivastava  - Laboratory PhLAM

Imagerie Temporelle Quantique avec Photons Uniques et Paires de Photons

Abstract :

This dissertation investigates diverse utilizations of temporal imaging systems in the domain of quantum communications and information processing tasks. Firstly, we propose an application of quantum temporal imaging to restore the indistinguishability of the signal and the idler photons produced in type-II spontaneous parametric down-conversion with a pulsed broadband pump. It is known that in this case, the signal and the idler photons have different spectral and temporal properties. We demonstrate that inserting a time lens in one arm of the interferometer and choosing properly its magnification factor restores perfect indistinguishability of the signal and the idler photons and provides 100% visibility of the Hong-Ou-Mandel interference in the limit of high focal group delay dispersion of the time lens. Secondly, we encounter that a single-time-lens imaging system always imparts a residual temporal chirp on the image, which may be detrimental for quantum networks, where the temporal image interacts with other fields. Therefore, we show that a two-time-lens imaging system satisfying the telescopic condition, a time telescope, is necessary and sufficient for creating a chirpless image. We also develop a general theory of a time telescope, find the conditions for loss minimization, and show how an erecting time telescope creating a real image of a temporal object can be constructed. Finally, we study the possibility of measuring the time-resolved second-order autocorrelation function of one of two beams generated in type-II parametric downconversion employing temporal magnification of this beam, bringing its correlation time from the picosecond to the nanosecond scale, resolvable by modern photodetectors. We show that such a measurement enables one to infer directly the degree of global coherence of that beam, which is linked by a simple relation to the number of Schmidt modes characterizing the entanglement between the two generated beams.

Keywords : Spontaneous parametric down-conversion,Temporal imaging systems,Entanglement,Hong-Ou-Mandel interference,Time telescope,Second-order autocorrelation function