We report on the first subpicometer interferometer flown in space. It was part of ESA’s Laser Interferometer Space Antenna (LISA) Pathfinder mission and performed the fundamental measurement of the positional and angular motion of two free-falling test masses. The interferometer worked immediately, stably, and reliably from switch on until the end of the mission with exceptionally low residual noise of ${32.0}_{-1.7}^{+2.4}\mathrm{fm}/\sqrt{\mathrm{Hz}}$, significantly better than required. We present an upper limit for the sensor performance at millihertz frequencies and a model for the measured sensitivity above 200 mHz.

• Received 10 September 2020
• Accepted 12 February 2021

DOI:https://doi.org/10.1103/PhysRevLett.126.131103

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Published by the American Physical Society