In 1954 Princeton University’s Robert Dicke predicted a remarkable phenomenon: A dense cloud of excited atoms in a light field, he argued, could decay by spontaneously emitting coherent and highly polarized photons—an effect he termed superradiance. By subtly altering the Hamiltonian, researchers in the early 1970s realized that the phenomenon need not be restricted to transient pulses, and they made their own prediction: When light and matter interact strongly enough, even at zero temperature, they can exhibit a steady-state superradiant phase.
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