The energy-level diagram of the dressed three-level system with position dependent AC Stark shift on the bright "coupling" state (that of the excited state is not shown, nor the blue-detuned virtual excited state, for clarity). The right process illustrates the gray molasses Sisyphus-like cooling cycle from the "bright" coupling state to the excited state to the "dark" non-coupling state. The left process depicts the nonadiabatic coupling between the bright and dark states that results from the action of the bare Hamiltonian. Figure adapted from T.W. Hänsch's seminal 1994 paper.
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