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Exponential improvement in photon storage fidelities using subradiance and selective radiance in atomic arrays - Darrick Chang - Mardi 30 mai 2017 à 16 h 30

INSP - UPMC - 4 place Jussieu - 75005 Paris - Barre 22-23, 3e étage, salle 317

Darrick Chang - ICFO (Barcelone)


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 radiant » states, whose coupling to the nanophotonic modes are collectively enhanced while free-space emission is collectively suppressed at the same time. Analyzing a protocol for a quantum memory for light that exploits these states, we find that an exponentially better suppression of errors is possible compared to the previously known bound.