  Nonlinear metasurfaces with subwavelength thickness were recently established
as versatile platforms for the enhanced and tailorable generation of entangled
photon pairs. The small dimensions and inherent stability of integrated
metasurface sources are attractive for free-space applications in quantum
communications, sensing, and imaging, yet this remarkable potential remained
unexplored. Here, we formulate and experimentally demonstrate the unique
benefits and practical potential of nonlinear metasurfaces for quantum imaging
at infrared wavelengths, facilitating an efficient protocol combining ghost and
all-optical scanning imaging. The metasurface incorporates a
subwavelength-scale silica metagrating on a lithium niobate thin film. Its
distinguishing feature is the capability to all-optically scan the photon
emission angle in the direction across the grating simply by tuning the pump
beam wavelength. Simultaneously, the photon emission is broad and
anti-correlated along the grating direction, allowing for ghost imaging.
Thereby, we reconstruct the images of 2D objects using just a 1D detector array
in the idler path and a bucket detector in the signal path, by recording the
dependencies of photon coincidences on the pump wavelength. Our results reveal
new possibilities for quantum imaging with ultra-large field of view and
improved imaging resolution as compared to photon pairs from conventional bulky
crystals. The demonstrated concept can be extended to multi-wavelength
operation and other applications such as quantum object tracking, paving the
way for advancements in quantum technologies using ultra-compact nanostructured
metasurfaces.
