In gravitational wave detectors, several pairs of mirrors are used to increase the amount of laser light stored along the massive arms of the detector. However, each of these pairs has tiny distortions that scatter light away from the perfect shape of the laser beam. This scattering can cause excess noise in the detector, limiting sensitivity, and ultimately forcing the instrument to shut down.

Two particles are considered entangled if their quantum states are correlated to such an extent that they cannot be described independently. This property is central to many areas of quantum technology, including schemes that use photons to exchange keys in quantum cryptography. Entanglement is, however, fragile, meaning that changing the frequency of one photon risks destroying its entanglement with another.