Pre-Submission Thesis Presentation

In this talk, I will present my doctoral research on the generation of entangled photons, development and implementation of Quantum Key Distribution (QKD) systems using photonic entanglement, while also focusing on the challenges posed by decoherence. Quantum mechanics offers a fundamentally new approach to secure communication, where QKD protocols promise information-theoretic security guaranteed by the laws of physics. However, the practical realization of such systems is faced with challenges, including photon loss, hardware limitations, and the detrimental effects of decoherence due to environmental interactions. During the first part of the talk, I will introduce the basic principles of quantum cryptography and photonic entanglement, followed by an overview of the experimental techniques used for processes such as entangled photon pair generation using spontaneous parametric down-conversion, and weak coherent pulse generation. 

A significant portion of the talk will focus on how decoherence affects quantum systems, particularly the phenomenon of Entanglement Sudden Death (ESD), where entanglement vanishes completely in finite time due to noisy environments. I will present our theoretical models, including a time-dependent framework developed to describe and analyze decohering channels studied through our experiments. I will go on to discuss experimental strategies we employed to mitigate the impact of decoherence, such as the use of local unitary operations to hasten, delay or avoid ESD in entangled systems. These experiments not only provide insight into the fundamental physics of open quantum systems but also play a critical role in enabling robust quantum communication and computing architectures. 

The final part of the talk will cover our experimental demonstrations of QKD in both laboratory and real-world free-space conditions. I will share results from our 50-meter free-space QKD system built in our institute campus, featuring a polarization correction technique developed in our previous work. I will also discuss briefly our work on a mobile QKD receiver development. By integrating theoretical modelling, photonic instrumentation, and experimental realizations, this thesis contributes to advancing our efforts in quantum-secure communication towards practical deployment. I will conclude with a discussion on future directions, including protocol development, decoherence control, and hardware advancements for ongoing projects.