Yuan Xu

Optical tweezer arrays have emerged as a key experimental platform^1,2 for quantum computation^3,4, quantum simulation^5,6 and quantum metrology^7,8, enabling unprecedented levels of control over single atoms and molecules. The ability to scale such arrays has become a defining challenge. Typically, optical tweezer arrays are generated using acousto-optic deflectors or liquid-crystal spatial light modulators. Fundamental limitations in optical resolution have constrained array sizes to about 10,000 traps⁹. Metasurfaces^10,11, planar photonic devices comprising millions of subwavelength pixels, provide an intriguing alternative for the generation of optical tweezer arrays¹². Here we demonstrate the trapping of single strontium atoms in optical tweezer arrays generated via holographic metasurfaces. We realize two-dimensional arrays with more than 100 single atoms, arranged in arbitrary geometries with trap spacings as small as 1.5 μm. The arrays have a high uniformity in terms of trap depth, trap frequency and positional accuracy, rivalling or surpassing existing approaches. This is enabled by highly efficient holographic metasurfaces fabricated from high-refractive-index materials, silicon-rich silicon nitride and titanium dioxide. Through analytical and numerical methods, we find that the subwavelength pixel sizes of these metasurfaces allow scaling of tweezer arrays far beyond current capabilities. As a demonstration, we realize an optical tweezer array with 360,000 traps. These advances overcome a critical barrier to realizing scalable neutral-atom quantum technologies.

Metasurfaces have been rapidly advancing our command over the many degrees of freedom of light; however, so far, they have been mostly limited to manipulating light in free space. Metasurfaces integrated on top of guided-wave photonic systems have been explored to control the scattering of light off-chip with enhanced functionalities—namely, the point-by-point manipulation of amplitude, phase or polarization. However, these efforts have so far been limited to controlling one or two optical degrees of freedom at best, as well as device configurations much more complex compared with conventional grating couplers. Here we introduce leaky-wave metasurfaces, which are based on symmetry-broken photonic crystal slabs that support quasi-bound states in the continuum. This platform has a compact form factor equivalent to the one of grating couplers, but it provides full command over the amplitude, phase and polarization (four optical degrees of freedom) across large apertures. We present devices for phase and amplitude control at a fixed polarization state, and devices controlling all the four optical degrees of freedom for operation at a wavelength of 1.55 μm. Merging the fields of guided and free-space optics through the hybrid nature of quasi-bound states in the continuum, our leaky-wave metasurfaces may find applications in imaging, communications, augmented reality, quantum optics, LIDAR and integrated photonic systems.