Ayan Biswas

The future quantum internet will leverage existing communication infrastructures, including deployed optical fibre networks, to enable novel applications that outperform current information technology. In this scenario, we perform a feasibility study of quantum communications over an industrial 224 km submarine optical fibre link deployed between Southport in the United Kingdom (UK) and Portrane in the Republic of Ireland (IE). With a characterisation of phase drift, polarisation stability and the arrival time of entangled photons, we demonstrate the suitability of the link to enable international UK–IE quantum communications for the first time.

This study focuses on improving practical QKD implementations using weak coherent pulses. We enhance the conventional decoy pulse method by integrating it with the coincidence detection (CD) protocol. Additionally, we introduce an easy-to-implement algorithm for computing asymptotic key rates. Through experimental implementation, we demonstrate that our approach significantly enhances key rates under realistic conditions by monitoring coincidences in the decoy state protocol.

Quantum Random Number Generators (QRNGs) are an integral part of cryptography. In this work, we exploit the relationship between the quality of randomness of discrete variable QRNGs(min-entropy(X)) and the quality of single photon source from SPDC sources (second-order correlation: g(2)(0)). This work provides another stitch between the two fields of information theory and quantum optics. We show the variation of the two parameters (min-entropy(X)) and b(=1- g(2)(0)) on various grounds, say, variation with orbital angular momentum (OAM) of the spatial mode, with time delay, etc. We propose a relationship between min-entropy(X) and g(2)(0) and also give a physical significance to min-entropy(X).