Abstract

The Laser Interferometer Gravitational-wave Observatory (LIGO) operates at the limit of quantum noise to detect gravitational waves (GWs) from cataclysmic cosmic events, such as the mergers of black hole and neutron star binaries. While the detectors already inject quantum light (“squeezed” vacuum) to reduce high-frequency quantum shot noise, this quantum enhancement comes at the cost of added low-frequency quantum noise due to opto-mechanical backaction. We have now commissioned the filter cavity upgrade to frequency-dependent squeezing in LIGO to mitigate quantum backaction across the astrophysically-critical band, demonstrating a new fundamental technology for our observatories. In the upcoming observing run of LIGO, our quantum-enhanced sensitivity will expand our astrophysical horizons by 60%, expected to bring detection rates from a near-weekly to near-daily -- just nine years after the dawn of GW astronomy.

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