by Prof. Krishna Thyagarajan, Former Professor of Physics, IIT Delhi

Abstract

 

For most of everyday experience, light behaves as an electromagnetic wave, a picture that explains rainbows, lenses, and radio alike. But some phenomena can't be understood this way: they require a quantum description in which light arrives in discrete packets called photons. This shift opens up a remarkable landscape of quantum states of light, including states with an exact number of photons, "squeezed" states whose noise dips below classical limits, and entangled states whose correlations no classical theory can reproduce. Far from being laboratory curiosities, these states now sit at the heart of emerging technologies such as quantum computing, secure communication through quantum key distribution, ultra-precise sensing, and quantum teleportation. This talk will explore what makes light quantum, introduce some of its most striking states, and explain why entangled photons have become a key resource for quantum photonics. It will also show how nonlinear optics, where intense light interacts with materials to create new light, has become one of the most powerful tools for generating and exploring these quantum states.

 

About Speaker

Since the 1970s, Prof. Krishna Thyagarajan's research at IIT Delhi has spanned fiber optics, integrated photonics, nonlinear guided-wave photonics, and quantum optics, including the generation of entangled photon pairs in waveguides. Apart from several publications and patents, he has co-authored multiple books on topics related to laser physics, fiber optics and recently on quantum photonics. He is a Fellow of the Optical Society of America (Optica) and of the Indian National Academy of Engineering.