Future Upgrades and Detectors for Ground-Based Gravitational-Wave Interferometry

Gravitational wave detection from the ground continues to push forward toward the fifth observing run and beyond, with a goal of ever-increasing astrophysical sensitivity. Greater sensitivity will deliver not just a greater rate of detections, but also detections made with higher fidelity, detections of more massive systems, and detections of systems at greater cosmological redshift. This will be enabled by a research program along multiple fronts: the pursuit of new materials for test masses and laser mirror coatings, superior seismic isolation, improved test mass suspension systems, and better control of the quantum optomechanical state of the detector. These technological improvements will first be deployed in the current gravitational-wave detector facilities, with an eye toward the development of detectors in new and larger facilities that would enable gravitational wave detections back to the time of the first stars.