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Enhancing atom-light interactions with subradiant states

October 17, 2016 - 11:00am
Darrick Chang
ICFO, Barcelona

Establishing efficient quantum interfaces between light and atomic media forms the basis for many important applications in quantum information science and metrology. The ultimate performance of such an interface is limited by the probability of interacting with a preferred mode of light over all others (e.g., free-space scattering), and leads to widely known figures of merit such as cooperativity in cavity QED or optical depth in atomic ensembles. These figures of merit are based upon the important assumption that scattering into free-space modes is independent, and an intriguing question is whether they can be improved upon by exploiting collective subradiant states of atomic ensembles where such scattering is strongly suppressed. We begin by elucidating the origin of subradiance in the elegant cases of free-space atomic lattices in 1D and 2D, where subradiance is associated with the existence of optical "guided modes" that cannot escape the lattice. We find that subradiant states in these systems have well-defined spatial structure and decay at a rate dictated by the density of atomic excitations. We then show how the optical depth limit can be exceeded by interfacing atomic lattices with nanophotonic structures. In particular, atom-light interactions can be made highly efficient by exploiting "selectively subradiant" states, whose coupling to the nanophotonic modes are collectively enhanced while free-space emission is collectively suppressed at the same time.

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