'Quantum weirdness' in exploitation by the international gravitational-wave observatory network

The detectors of the international gravitational-wave (GW) observatory network are currently taking data with sensitivities improved via squeezing the photon counting noise of the laser light used. Several GW candidate events, such as black-hole mergers, are already in the pipeline to be analyzed in detail. While the brand-new field of GW astronomy relies on squeezed light for reaching higher sensitivities, the physical understanding of such light, although being well-described by quantum theory, is still under discussion. Here, I present a description of why squeezed light, as now being exploited by GW observatories, constitutes rather remarkable physics. I consider the squeezed photon statistics and show its relation to the famous gedanken experiment formulated by Einstein, Podolsky, and Rosen in 1935. My description illuminates ‘quantum weirdness’ in a clear way and might be the starting point for finding the physics of quantum correlations in general, which scientists have been seeking for decades.