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Two-dimensional double-quantum spectra reveal collective resonances in an atomic vapor (1112.0336v1)
Published 1 Dec 2011 in physics.atom-ph, physics.chem-ph, and physics.optics
Abstract: We report the observation of double-quantum coherence signals in a gas of potassium atoms at twice the frequency of the one-quantum coherences. Since a single atom does not have a state at the corresponding energy, this observation must be attributed to a collective resonance involving multiple atoms. These resonances are induced by weak inter-atomic dipole-dipole interactions, which means that the atoms cannot be treated in isolation, even at a low density of $10{12}$ cm${-3}$.