  Metasurface-based optical elements typically manipulate light waves by
imparting space-variant changes in the amplitude and phase with a dense array
of scattering nanostructures. The highly-localized and low
optical-quality-factor (Q) modes of nanostructures are beneficial for
wavefront-shaping as they afford quasi-local control over the electromagnetic
fields. However, many emerging imaging, sensing, communication, display, and
non-linear optics applications instead require flat, high-Q optical elements
that provide notable energy storage and a much higher degree of spectral
control over the wavefront. Here, we demonstrate high-Q, nonlocal metasurfaces
with atomically-thin metasurface elements that offer notably enhanced
light-matter interaction and fully-decoupled optical functions at different
wavelengths. We illustrate a possible use of such a flat optic in eye tracking
for eye-wear. Here, a metasurface patterned on a regular pair of eye-glasses
provides an unperturbed view of the world across the visible spectrum and
redirects near-infrared light to a camera to allow imaging of the eye.
