Three-dimensional magneto-optical trap beam delivery with scalable wafer-level optics

Magneto-optical traps (MOTs) are essential for preparing and capturing cold atoms in precision atomic applications. Conventional free-space beam delivery systems are bulky, expensive, and difficult to align. Current photonic integrated circuit (PIC) MOT approaches though scalable still require manual alignment of external quarter-wave plates (QWPs) and mirrors, limiting miniaturization and reduction of complexity. Here, we present a two-wafer beam delivery architecture for a PIC-based MOT using an inverse-designed multi-functional grating coupler and integrated metasurface retroreflectors, eliminating the need for all external optics. Both components are designed via inverse optimization to deliver circularly polarized light for 87Rb at 780 nm. We experimentally demonstrate retroreflector with 74% efficiency and 0.88 ellipticity, meeting performance requirements for MOT operation. The grating coupler is characterized through full-wave electromagnetic simulations, showing 20% out-coupling efficiency and 0.85 polarization ellipticity. This two-wafer architecture proposed here significantly simplifies alignment and maintains a compact, scalable foundry-compatible footprint for all beam-delivery components.