Optical Sources for Applications in Quantum Technologies

Quantum light sources play a foundational role in a wide range of emerging quantum technologies, from secure communication to precision measurement and sensing. Here, we report experimental advances at the Indian Institute of Technology Madras, where we have developed a variety of home-built sources and testbeds tailored to application-driven studies. Using fiber-based four-wave mixing, we generate correlated photon pairs with frequency-comb structure, enabling tunable and spectrally flexible non-classical states. We demonstrate simultaneous multimode excitation in a Sagnac-based entangled-photon source, providing a scalable platform for polarization entanglement. We present a machined bow-tie cavity for squeezed-light generation, along with mode analysis of Hermite-Gaussian modes using a spatial light modulator (SLM). In parallel, we develop rare-earth-doped fiber lasers that provide stable and narrow-linewidth operation as practical pump sources for quantum optics experiments. We further outline proposals for quantum-imaging experiments exploiting undetected photon schemes to achieve near-infrared imaging with visible detection, and for high-dimensional entanglement generation using orbital angular momentum states characterized via a Zou-Wang-Mandel interferometer. Together, these platforms illustrate the versatility of optical architectures in producing and manipulating non-classical states of light, and they position IIT Madras as a key contributor to the broader effort of building scalable quantum photonic technologies in India.