Collective emission of light by atomic ensembles

4 problems

• Threshold for a Dicke superradiant burst in ordered atom arrays

  Partially resolved

  Excited atoms packed close enough emit a bright burst instead of glowing steadily. The minimum closeness needed in a regular array is predicted only approximately.

• Continuous superradiant laser on a millihertz atomic clock transition

  Open

  A laser whose light is stored in atoms rather than mirrors could be far more stable than today's best lasers, because mirror vibrations would barely matter. Short bursts have been shown on a strontium clock line, but a laser that runs continuously has not.

• What limits the refractive index of a dense atomic gas?

  Partially resolved

  Each atom bends light strongly, yet no known material made of atoms has a refractive index far above a few. Packing atoms denser does not help, and the reason is not fully settled.

• Lifetime scaling of the most subradiant state in 2D arrays

  Open

  Some collective states of atom arrays emit light extremely slowly and could store photons. How their lifetime grows with array size and how disorder shortens it are not known for 2D arrays.