High efficiency large-angle polarization-insensitive retroreflecting metasurface for magneto-optical traps.

This article focuses on the design, fabrication, and characterization of a planar retroreflecting metasurface intended to miniaturize three-dimensional magneto-optical traps (3D-MOTs), which are critical for atomic clocks, quantum computing, and cold-atom science. The metasurface, optimized via Bayesian inverse design, achieves high-efficiency, polarization-insensitive retroreflection of circularly polarized light at large incidence angles, replacing bulky free-space mirrors and quarter wave plates traditionally used in 3D-MOT setups. Experimental results at 736 nm demonstrate near-ideal retroreflection performance, with deviations from the target 780 nm wavelength attributed to oxidation of amorphous silicon nanopillars; mitigation strategies including material substitution and design adjustments are discussed. This work represents the first demonstration of a metasurface capable of preserving circular polarization upon retroreflection and marks a significant step toward fully integrated, compact 3D-MOT systems for applications beyond laboratory environments.