Near-symmetric multiport beam splitting for high-NOON state preparation on nonlocal metasurface

Polarization beam splitting (BS) has been implemented on gradient metasurface with local response for entanglement manipulation and state reconstruction. To realize more degrees of light modulation, nonlocal modes, manifested as wavelength and momentum selectivity, should be applied into metasurface BS. Here, we demonstrate that single nonlocal phase gradient metasurface(NPGM) can function as a series of independent near-symmetric multiport BS,constructed by its momentum-polarization mode subspaces.Then, using any of above BS with simultaneous multiphoton interference, high-photon NOON states are prepared with high success probability and fidelity. For example,four-mode four-photon NOON state is obtained with 34.8% success probability and fidelity of 99.9%, greatly higher than those previously reported.With unique capability of multiphoton interference, this multiport BS on single NPGM can be directly used in the on-chip quantum photonics. Also, the efficient generation of high-photon NOON states with above BS has potential applications in quantum precision measurement.