Researchers develop a light source that produces two entangled light beams

https://phys.org/news/2023-01-source-entangled.html

"optical parametric oscillator (OPO) light source made of non-linear optical response crystal between two mirrors forming optical cavity. Shine bright green beam on apparatus, crystal-mirror dynamics produces two light beams (actually produced four) with quantum correlations... critical: intensity, beams' phases, light wave synchronization, temperature (not too hot)... use of rubidium OPOs more efficient than crystal OPOs since avoids the need for mirrors to imprison the light for such a long time"

Related: Researchers create 2D quantum light source from layered materials

https://phys.org/news/2023-01-2d-quantum-source-layered-materials.html