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Listening to the quantum vacuum

Since the historic finding of gravitational waves from two black holes colliding over a billion light-years away was made in 2015, physicists are advancing knowledge about the limits on the precision of the measurements that will help improve the next generation of tools and technology used by gravitational wave scientists. Now, a team of National Science Foundation-funded researchers is presenting the first broadband, off-resonance measurement of quantum radiation pressure noise in the audio band, at frequencies relevant to gravitational wave detectors. The results hint at methods to improve the sensitivity of gravitational-wave detectors by developing techniques to mitigate the imprecision in measurements called "back action," thus increasing the chances of detecting gravitational waves. The researchers have developed physical devices that make it possible to observe -- and hear -- quantum effects at room temperature. It is often easier to measure quantum effects at very cold temperatures, while this approach brings them closer to human experience. Housed in miniature models of detectors like the Laser Interferometer Gravitational-Wave Observatory (LIGO), these devices consist of low-loss, single-crystal "micro-resonators" -- each a tiny mirror pad the size of a pin prick, suspended from a cantilever. A laser beam is directed at one of these mirrors and as the beam is reflected, the fluctuating radiation pressure is enough to bend the cantilever structure, causing the mirror pad to vibrate, which creates noise.

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