Realization of two-dimensional spin-orbit coupling for Bose-Einstein condensates

Spin-orbit coupling in an optical lattice Studying topological matter in cold-atom systems may bring fresh insights, thanks to the intrinsic purity and controllability of this experimental setting. However, the necessary spin-orbit coupling can be tricky to engineer. Wu et al. conceived and experimentally demonstrated a simple scheme that involves only a single laser source and can be continuously tuned between one- and two-dimensional spin-orbit coupling (see the Perspective by Aidelsburger). Although this experiment used bosonic atoms, it is expected that the setup would also work for fermions. Science, this issue p. 83; see also p. 35 Rubidium atoms are used to demonstrate a spin-orbit coupling scheme that is tunable between the 1- and 2D limits. [Also see Perspective by Aidelsburger] Cold atoms with laser-induced spin-orbit (SO) interactions provide a platform to explore quantum physics beyond natural conditions of solids. Here we propose and experimentally realize two-dimensional (2D) SO coupling and topological bands for a rubidium-87 degenerate gas through an optical Raman lattice, without phase-locking or fine-tuning of optical potentials. A controllable crossover between 2D and 1D SO couplings is studied, and the SO effects and nontrivial band topology are observed by measuring the atomic cloud distribution and spin texture in momentum space. Our realization of 2D SO coupling with advantages of small heating and topological stability opens a broad avenue in cold atoms to study exotic quantum phases, including topological superfluids.

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