Squeezing for quantum sensing: Pushing gravitational-wave detection beyond the quantum limit

Abstract: The Heisenberg uncertainty principle dictates that the position and momentum of an object cannot be simultaneously measured with arbitrary precision, giving rise to an apparent limitation known as the standard quantum limit (SQL). Gravitational-wave detectors use photons to continuously measure the positions of freely falling mirrors, so are affected by the SQL. We investigate the performance of the Laser Interferometer Gravitational-wave Observatory (LIGO) after the experimental realization of frequency-dependent squeezing designed to surpass the SQL. For the LIGO Livingston detector, we find the upgrade reduces quantum noise below the SQL by a maximum of three decibels between 35 to 75 Hz while achieving broadband sensitivity improvement, increasing the overall detector sensitivity during astrophysical observations.