Ravindra Pratap Singh

Continuous-variable quantum key distribution (CVQKD) enables practical quantum communication using standard telecommunication technologies. Unidimensional CVQKD (UD-CVQKD) reduces experimental complexity by encoding information in a single quadrature of optical fields, unlike conventional two-quadrature implementations. In this work, we experimentally demonstrate a free-space Gaussian modulated UD-CVQKD system using polarized coherent states. The security performance is analyzed under both trusted and untrusted detector noise models. Positive key rates are obtained for both models, achieving up to 0.79 bits/pulse (trusted detector) and 0.68 bits/pulse (untrusted detector) under optimal conditions. The dependence of system parameters on Alice’s modulation variance is also experimentally investigated, showing a decrease in key rate with increasing modulation variance.

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).