Transition-Edge Sensors at the Forefront of Cosmology

For well over a decade, the high sensitivity and background-limited performance of transition-edge sensor (TES) bolometers have made them the technology of choice for ground-based observations of the cosmic microwave background (CMB). This relic radiation from the early universe contains a wealth of information on the expansion history of the universe and the relative abundances of different forms of matter and energy present in it. Observations of the CMB form a pillar of the modern Standard Model of cosmology, and measurements taken with ever-greater precision test that model and probe the physics at the very beginning of the universe. To make increasingly sensitive measurements of the CMB, ever-larger arrays of TESs are being fielded in telescopes observing the millimeter-wave sky. Kilopixel-scale cameras that were common ten years ago have been replaced with receivers containing ten thousand or tens of thousands of TES devices, read out with increasingly sophisticated multiplexing schemes to limit the wiring complexity and thermal load on the cryogenic focal planes. Beyond this, the next phase of CMB experiment is already in development and plans to put on order of 500,000 TESs on sky, requiring a significant leap forward in TES fabrication and characterization.