A little while ago I pondered allotropic bromine, or Br(Br) 3 . But this is a far wackier report[cite]10.1126/science.aao7293[/cite] of a molecule of light. The preparation and detection of dimer and trimer bound photon states is pure physics; probably considered by the physicists themselves as NOT chemistry. It is certainly true, as a chemist, that I understood only a little of the article.
Forming photonic bound states Photons do not naturally interact with each other and must be coaxed into doing so. Liang et al. show that a gas of Rydberg atoms—a cloud of rubidium atoms excited by a sequence of laser pulses—can induce strong interactions between propagating photons. The authors could tune the strength of the interaction to make the photons form dimer and trimer bound states. This approach should prove useful for producing novel quantum states of light and quantum entanglement on demand. Science , this issue p. 783