We theoretically demonstrate nonlocal phase gradient metasurfaces can function as a series of near-symmetric multiport beam splitting, through which we prepare multimode high-photon NOON states through multiphoton interference with high success probability and fidelity.
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.
Local gradient metasurfaces have realized multiple beam splitting (BS) functions, enabling various applications in on-chip quantum information. However, nonlocal metasurface BS with the utilization of wavelength and momentum selectivity remains unexplored. Here, we demonstrate the framework of a multi-degree-of-freedom multiport BS on a single nonlocal phase gradient metasurface. The BS, constructed by its momentum-polarization mode subspaces, is co-modulated by wavelengths, polarization, and angles of incident light. With the unique capability of multimode interference, this multiport BS can facilitate quantum state engineering, especially multimode high-dimensional quantum entanglement. Then, four-mode high-photon NOON states, manifested as polarization-path-locked properties, are prepared with high success probability and fidelity. For example, four-photon and eight-photon NOON states are obtained with success probabilities of 33.7% and 12.5%, respectively. The efficient generation of multimode high-photon NOON states on a single metasurface improves the precision of on-chip quantum measurement and significantly enhances the integration of quantum information platforms.
Gradient metasurface, formed by a set of subwavelength unit cells with different phase modulation, is widely used in polarized beam splitting (BS) in the classical and quantum optics. Specifically, its phase gradient allows the path and polarization of multiple output lights to be locked by corresponding inputs.Using this unique path-polarization locked property, we demonstrate that the single metasurface can function as sequentially linked beamsplitters, enabling the parallelization of a series of BS processes. Such a parallel BS metasurface provides a multi-beam interference capability for both classical and quantum light manipulation. Taking this advantage, we first prepare path and polarization hybrid entangled states of two, three, and multi photons from unentangled photon sources. Then, the ability of parallel BS-facilitated entanglement is applied to demonstrate entanglement fusion among entangled photon pairs, which can greatly enlarge the entanglement dimension. The principle of parallel BS through the metasurface opens up a versatile way to manipulate the quantum state at the micro/nano scale, which will have potential applications in on-chip quantum optics and quantum information processing.