From quantum ripples to superconducting pixels: toward CMB polarization with kinetic inductance detectors

The polarization of the Cosmic Microwave Background (CMB) carries unique information about the physics of the early Universe, including primordial density fluctuations and a possible background of inflationary gravitational waves. Extracting this signal requires detectors operating at extreme sensitivity, capable of measuring minute polarization anisotropies while controlling instrumental systematics at an unprecedented level. In this seminar, I will first review the physical origin of CMB polarization, introducing E- and B-modes and highlighting their connection to fundamental questions in high-energy and particle physics. I will then present Kinetic Inductance Detectors (KIDs), superconducting resonators in which incident photons break Cooper pairs, producing measurable shifts in kinetic inductance and resonance frequency. Their intrinsic frequency multiplexing and scalability make them compelling candidates for large-format millimeter-wave experiments. Although KIDs have not yet been deployed in a dedicated CMB polarization experiment, I will show that recent experimental results demonstrate their readiness for this challenge. I will discuss detector performance, noise properties, optical response, polarization sensitivity, and systematic control, outlining the path from laboratory validation to cosmological application. This work illustrates how advances in superconducting detector technology can help enable the next generation of precision measurements of the early Universe.