CLOUDS of atoms can hide their light. When an atom moves to a lower-energy state, it emits a particle of light called a photon. But this process can be delayed and photons trapped in a dense cloud of atoms. This may eventually prove useful for quantum devices that communicate using light.When an atom absorbs a photon, exciting it to a higher-energy state, it will always release that photon and return to its initial state in about the same amount of time. When this is delayed, it is called subradiance.
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