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Pauli blocking of atom-light scattering

Description Photons not welcome Two identical fermions cannot occupy the same quantum state, or so says the Pauli principle. For a cold gas of fermionic atoms, this means that all states up to the Fermi energy will be occupied, with only the atoms with the highest energy able to change their state. Such conditions have long been predicted to suppress light scattering off gases because the atoms receiving a kick from collisions with photons would have no state to move to. Deb et al., Margalit et al., and Sanner et al. now describe this so-called Pauli blocking of light scattering. —JS Lack of empty final states leads to the suppression of light scattering off an ultracold gas of fermionic atoms. Transition rates between coupled states in a quantum system depend on the density of available final states. The radiative decay of an excited atomic state has been suppressed by reducing the density of electromagnetic vacuum modes near the atomic transition. Likewise, reducing the density of available momentum modes of the atomic motion when it is embedded inside a Fermi sea will suppress spontaneous emission and photon scattering rates. Here we report the experimental demonstration of suppressed light scattering in a quantum degenerate Fermi gas. We systematically measured the dependence of the suppression factor on the temperature and Fermi energy of a strontium quantum gas and achieved suppression of scattering rates by up to a factor of 2 compared with a thermal gas.