Strongly quadrature-squeezed light from a single multilevel atom

We propose schemes for steady-state emission of quadrature-squeezed light from a single-atom cavity quantum electrodynamics system. Two effective atom-cavity interaction models are suggested, motivated by correlated photon-pair emissions and multiphoton coherences that manifest themselves as squeezing of light emitted from the cavity. We consider idealized models to examine the mechanisms and optimal regimes for generating squeezed light. We also demonstrate realizations of these models based on both single $^{87}\mathrm{Rb}$ and $^{133}\mathrm{Cs}$ atoms, using combinations of laser- and laser-plus-cavity-driven Raman transitions between magnetic sublevels in a single ground hyperfine state. We show that these systems can in principle produce a much stronger level of squeezing than has previously been possible from a single-atom source.