Author(s): Amit Singh Ubhi, Lari Koponen, Jiri Smetana, Yulin Xia, Haixing Miao, Emilia Chick, John Bryant, Geraint Pratten, Teng Zhang, Richard Mittleman, Peter Fritschel, Alan V. Cumming, Giles Hammond, and Denis Martynov Extending the sensitivity of terrestrial gravitational-wave detectors below 20 Hz is a long-standing challenge, limited by ground motion and inertial sensing noise. In this Letter, we demonstrate ultra-high-vacuum compatible inertial isolation and position sensing technologies that achieve active pl… [Phys. Rev. Lett. 137, 031401] Published Thu Jul 16, 2026