A nano-optical transistor for photonics is switched with a few photons https://www.mpg.de/10478678/photonics-nanooptical-transistor
Photonics: V.Sandoghdar’s team at the Max Planck Institute for the Science of Light has presented a nano-optical transistor that is switched by a few photons.
cooled molecules which they had embedded in a solid matrix to minus 272 degrees Celsius