Light from many tiny emitters — atoms or artificial "quantum dots"—usually scatters in all directions, like a crowd where everyone shouts on their own. But if you make them "sing in chorus," the flash becomes many times brighter. Such coherent emission is called superradiance, and until now it required emitters to be almost touching — at distances smaller than the wavelength of light.
A new idea uses a flat structure — a metasurface made of a transparent dielectric with a carved pattern. Inside it, a special light mode arises that does not leak out but lives within, yet extends over large distances. This mode — a "bound state in the continuum" (BIC)—acts as a common stage where distant emitters begin to oscillate in step. Even if they are spaced several wavelengths apart, their light combines into a single powerful wave.
The scientists showed that such a system can reach the theoretical Dicke limit — the maximum possible brightness of collective emission. For this, the emitters must interact strongly enough with the BIC mode (characterized by the so-called beta factor). Calculations also confirmed that the effect is robust to real imperfections: small variations in emitter positions or material losses.
This approach paves the way for creating bright light sources where many weak emitters combine into one powerful one, without needing to pack them too densely. This could be useful in lasers, sensors, and quantum devices.
Dicke superradiance is named after physicist Robert Dicke, who in 1954 predicted that a group of atoms could emit light much more intensely than each atom individually if they act coherently.
In Arthur C. Clarke's novel "The Light of Other Days," the idea of collective observation through "wormholes" is used, but the principle of coherent amplification of signals from many sources echoes superradiance.