An ideal system is a highly reflecting mirror whose motion is sensed by monochromatic light, which is photoelectrically detected with high quantum efficiency. A quantum optomechanical experiment is achieved if the quantum uncertainties of light and mirror motion influence each other, ultimately leading to the observation of entanglement between optical and motional degrees of freedom. In AVS Quantum Science, researchers from Hamburg University in Germany review research on gravitational wave detectors as a historical example of quantum technologies and examine the fundamental research on the connection between quantum physics and gravity. Gravitational wave astronomy requires unprecedented sensitivities for measuring the...