Victoria Xu, MIT

"Expanding our gravitational view of the Universe with quantum interferometry"

Abstract: From atom interferometry to laser interferometry, experiments are leveraging quantum mechanics to expand our gravitational view of the Universe. In atom interferometry, we have realized ultra-long coherence times for these spatially-separated massive quantum superpositions, which we can use for precise atomic gravimetry. In laser interferometry, as one of the most sensitive displacement sensors ever built, the Advanced Laser Interferometer Gravitational-wave Observatory (Advanced LIGO) operates at the limit of quantum noise to detect gravitational waves from cataclysmic astrophysical events, such as the mergers of black holes and neutron stars. Ongoing quantum upgrades to the Advanced LIGO detectors will be the primary focus of this talk. Already, the detectors inject quantum light (“squeezed” vacuum) to reduce high-frequency quantum noise from shot noise. Major upgrades are in progress to additionally reduce the low-frequency quantum noise that results from opto-mechanical backaction. This involves coupling our squeezed light source to a 300-m long, narrow-band “filter” cavity, which rotates the squeezing quadrature below 100 Hz to evade low-frequency quantum noise in the astrophysically-critical band. This low-frequency squeeze rotation will at last configure the LIGO interferometers for optimal sensing below the standard quantum limit. In the next observing run, together with our growing international LIGO-Virgo-KAGRA (LVK) network of observatories, these quantum technologies will help bring gravitational wave detection from a near-weekly to near-daily occurrence, expanding the observable horizon of gravitational-wave astronomy.