Gravitational-wave detection beyond the quantum limit

Quantum technologies are rapidly expanding the observable horizon of gravitational-wave astrophysics. The Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) consists of twin quantum-limited, 4-km, Michelson laser interferometers, configured to detect the gravitational radiation from cataclysmic cosmic events such as the merger of black holes and neutron star binaries. At LIGO, we have recently commissioned large-scale quantum upgrades to detect gravitational waves with interferometric precision exceeding the standard quantum limit (SQL). This advance is possible with our introduction of a high-finesse, long-baseline filter cavity for frequency-dependent squeezed light injection – a substantial upgrade from our initial year-long observing run with broadband squeezing. The filter cavity rotates the quadrature squeezing angle at low frequencies to evade opto-mechanical backaction, and enable broadband quantum noise reduction for sub-SQL gravitational-wave detection in our upcoming astrophysical observing run. We will present on recent quantum upgrades to the Advanced LIGO detectors, and showcase the profound impact of quantum enhancement on gravitational-wave astrophysics.