Identifying topological edge states in 2D optical lattices using light scattering

The European Physical Journal Special Topics - Tập 217 - Trang 135-152 - 2013
Nathan Goldman1, Jérôme Beugnon2, Fabrice Gerbier2
1Center for Nonlinear Phenomena and Complex Systems, Université Libre de Bruxelles (U.L.B.), Brussels, Belgium
2Laboratoire Kastler Brossel, CNRS, ENS, UPMC, Paris, France

Tóm tắt

We recently proposed in a Letter [Phys. Rev. Lett. 108, 255303] a novel scheme to detect topological edge states in an optical lattice, based on a generalization of Bragg spectroscopy. The scope of the present article is to provide a more detailed and pedagogical description of the system – the Hofstadter optical lattice – and probing method. We first show the existence of topological edge states, in an ultra-cold gas trapped in a 2D optical lattice and subjected to a synthetic magnetic field. The remarkable robustness of the edge states is verified for a variety of external confining potentials. Then, we describe a specific laser probe, made from two lasers in Laguerre-Gaussian modes, which captures unambiguous signatures of these edge states. In particular, the resulting Bragg spectra provide the dispersion relation of the edge states, establishing their chiral nature. In order to make the Bragg signal experimentally detectable, we introduce a “shelving method”, which simultaneously transfers angular momentum and changes the internal atomic state. This scheme allows to directly visualize the selected edge states on a dark background, offering an instructive view on topological insulating phases, not accessible in solid-state experiments.

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