Superradiance in multi-level atoms

Superradiance is an emergent phenemona whereby a large ensemble of emitters relaxes via a short intense burst of light rather than the exponential decay associated to single emitters. As originally formulated by Dicke in the 1950s, superradiance was considered from an ensemble of emitters contained within a volume with dimensions much smaller than the wavelength of the emitted light. The small volume allows for an approximation of all atoms to be permutationally symmetric, but is hard to achieve in physical systems. Superradiance will still occur outside this regime, but in a form modified by the loss of permutational symmetry. The nature of the many-body decay is controlled by dissipative interactions resulting from the interference of emitted fields, depending on the relative positions of the emitters and how the field propagates between them. Control over the many-body decay can thus be achieved through the geometry of the emitters. Arranging emitters in ordered arrays is a particularly promising avenue to explore many-body decay, highlighting the path towards controlled superradiance in neutral atoms in optical lattices. While real atoms are not necessarily two-level systems, we show that this is not a roadblock to observing superradiance, and that superradiance actually makes the atoms more two-level-like by closing off weaker decay channels. Multi-level systems also offer the ability to engineer decay. By off-resonantly driving emitters in ground states, one can generate Raman transitions between ground states, creating effective decay via a two-photon process. This effective emission is mediated by absorbing a laser photon and spontaneous emission, inheriting the properties of both. The frequency of the emitted fields are set by the dressing lasers, so dissipative interactions are only generated between atoms driven by the same laser. This allows for the production of dissipative interaction networks with connectivity not limited by a real space geometry.