Metasurface enables the generation and manipulation of multiphoton
entanglement with flat optics, providing a more efficient platform for
large-scale photonic quantum information processing. Here, we show that a
single metasurface optical chip would allow more efficient characterizations of
multiphoton entangled states, such as shadow tomography, which generally
requires fast and complicated control of optical setups to perform projective
measurements in different bases, a demanding task using conventional optics.
The compact and stable device here allows implementations of general positive
observable value measures with a reduced sample complexity and significantly
alleviates the experimental complexity to implement shadow tomography.
Integrating self-learning and calibration algorithms, we observe notable
advantages in the reconstruction of multiphoton entanglement, including using
fewer measurements, having higher accuracy, and being robust against optical
loss. Our work unveils the feasibility of metasurface as a favorable integrated
optical device for efficient characterization of multiphoton entanglement, and
sheds light on scalable photonic quantum technologies with ultra-thin
integrated optics.Comment: 15 pages, 9 figure