Entanglement witnessing is essential for quantum technologies such as computing, key distribution, and networking. Conventional bulk-optics methods require sequential reconfiguration across multiple polarization bases, limiting efficiency and scalability. We propose a metasurface-based analyzer that performs dual-basis (σ_z and σ_y) projections simultaneously by mapping them to orthogonal spatial modes. This allows direct access to the commuting two-photon correlators \langle σ_z \otimes σ_z \rangle and \langle σ_y \otimes σ_y \rangle required for entanglement witnessing. The metasurface design employs meta-atoms engineered to impart independent linear and circular phase delays through anisotropy and geometric control, resulting in polarization-dependent beam deflection that separates H/V and R/L components. This approach halves the measurement overhead compared to sequential analysis while offering a compact, integrable platform for chip-scale quantum photonics. The proposed scheme provides a path toward efficient entanglement verification with applications in quantum key distribution, quantum repeaters, and scalable quantum networks.
Entanglement witnessing is essential for quantum technologies such as computing, key distribution, and networking. Conventional bulk-optics methods require sequential reconfiguration across multiple polarization bases, limiting efficiency and scalability. We propose a metasurface-based analyzer that performs dual-basis (σ_z and σ_y) projections simultaneously by mapping them to orthogonal spatial modes. This allows direct access to the commuting two-photon correlators \langle σ_z \otimes σ_z \rangle and \langle σ_y \otimes σ_y \rangle required for entanglement witnessing. The metasurface design employs meta-atoms engineered to impart independent linear and circular phase delays through anisotropy and geometric control, resulting in polarization-dependent beam deflection that separates H/V and R/L components. This approach halves the measurement overhead compared to sequential analysis while offering a compact, integrable platform for chip-scale quantum photonics. The proposed scheme provides a path toward efficient entanglement verification with applications in quantum key distribution, quantum repeaters, and scalable quantum networks.
Bell nonlocality is both a defining signature of entanglement and a key quantum information resource. However, visualizing and certifying nonlocal correlations across a spatially multimode photonic field remains challenging due to the rapidly growing measurement cost of spatially resolved projective tests. To address this issue, we build a spatial nonlocality imaging scheme that directly reveals the spatial distribution of quantum nonlocality by integrating a metasurface that performs parallel polarization projections with a quantum-adaptive neural network. Spatially resolved Clauser--Horne--Shimony--Holt (CHSH) tests are realized over a 400-pixel biphoton field using an average of only 1.7 detected coincidence pairs per pixel per basis. This approach yields a nonlocality image that maps the two-dimensional spatial distribution of Bell violations across the optical field and reveals the target-state-dependent spatial evolution of Bell violations. It provides a highly resource-efficient route to large-scale Bell certification and opens new possibilities for exploiting spatially multimode entanglement in quantum imaging, quantum networking, and scalable photonic quantum technologies.
Summary form only given. Measurements of quantum states of photons are conventionally performed with series of optical elements in bulk setups [1] or optical chips incorporating multiple tunable beam splitters. Here, we suggest and develop experimentally, for the first time to our knowledge, a new concept of quantum-polarization measurements with a single all-dielectric resonant metasurface [2]. The operating principle is presented in Fig. 1(a): A metasurface spatially splits different components of photon polarization states, which then enables full reconstruction of the photon state based on the photon correlations with simple polarization-insensitive single-photon detectors or EMCCD cameras. The subwavelength thin structure provides an ultimate miniaturization, and can facilitate quantum tomography by spatially-resolved imaging without a need for reconfiguration. Such parallel-detection approach promises not only better robustness and scalability, but also the possibility to study the dynamics of quantum states in real-time.
Entanglement-based quantum science exploits subtle properties of quantum mechanics into applications such as quantum computing, sensing, and metrology. The emerging route for quantum computing applications, which calls for ultracompact, integrated, and scalable architecture, aims at on-chip entangled qubits. In this context, quantum entanglement among atomic qubits was achieved via cold-controlled collisions which are only significant at subwavelength separations. However, as other manifolds of quantum state engineering require single-site addressability and controlled manipulation of the individual qubit using diffraction-limited optics, entanglement of qubits separated by macroscopic distances at the chip level is still an outstanding challenge. Here, we report a novel platform for on-chip quantum state engineering by harnessing the extraordinary light-molding capabilities of metasurfaces. We theoretically demonstrate quantum entanglement between two qubits trapped on a chip and separated by macroscopic distances, by engineering their coherent and dissipative interactions via the metasurface. Spatially scalable interaction channels offered by the metasurface enable robust generation of entanglement, with large values of concurrence and remarkable revival from sudden death. The metasurface route to quantum state engineering opens a new paradigm for on-chip quantum science and technologies.
Beamsplitters represent fundamental components in both classical and quantum optical systems, enabling the distribution of light, as well as the generation of interference, superposition and entanglement. However, optical networks constructed from conventional bulk 2x2-beamsplitters encounter inherent scalability issues, as the number of required beamsplitters scales quadratically with the number of optical modes for a fully connected network. Metasurfaces offer a promising route to overcome these constraints. By manipulating light at the wavelength scale compact optical components with advanced functionalities can be constructed, which address several modes simultaneously. In this work, we design and experimentally utilize a metasurface as a multiport beamsplitter. Furthermore, we realize a multimode interferometer composed of two cascaded metasurfaces. We characterize the individual and cascaded metasurfaces using classical light, showing controllable splitting ratios through tunable phase relations. We then expand the approach to quantum light, employing single photons to demonstrate second- and third-order photon correlations, as well as single photon interference across multiple spatial paths. These results establish metasurface-based multiport beamsplitters as a scalable and reconfigurable platform bridging classical and quantum photonics.
Beamsplitters represent fundamental components in both classical and quantum optical systems, enabling the distribution of light, as well as the generation of interference, superposition, and entanglement. However, optical networks constructed from conventional bulk 2 × 2-beamsplitters encounter inherent scalability issues, as the number of required beamsplitters scales quadratically with the number of optical modes for a fully connected network. Metasurfaces offer a promising route to overcome these constraints. By manipulating light at the wavelength scale, compact optical components with advanced functionalities can be constructed, which address several modes simultaneously. In this work, we design and experimentally utilize a metasurface as a multiport beamsplitter. Furthermore, we realized a multimode interferometer composed of two cascaded metasurfaces. We characterize the individual and cascaded metasurfaces by using classical light, showing controllable splitting ratios through tunable phase relations. We then expand the approach to quantum light, employing single photons to demonstrate second- and third-order photon correlations as well as single photon interference across multiple spatial paths. These results establish metasurface-based multiport beamsplitters as a scalable and reconfigurable platform bridging classical and quantum photonics.
Manipulating photoluminescence from solid-state quantum emitters (QEs) on demand is of central importance for advanced quantum nanophotonic technologies. In comparison with conventional free-space approaches relying on bulky optical components, emitter-integrated metasurfaces provide a compact and efficient route for shaping photon emission directly at the source. Recent progress has established a common platform in which QE-excited surface plasmon polaritons (SPPs) are transformed by surrounding metasurfaces into free-space radiation with tailored propagation direction, polarization state, relative intensity, and spatial structure. This review highlights two complementary strategies that have recently been utilized for shaping quantum emission. The first is emitter-coupled meta-optics, which enables versatile photon sources with arbitrary polarization states, off-normal directionality, and multichannel emission by means of phase-engineered anisotropic meta-atoms. The second is vectorial scattering holography, including multiplexed implementations, which allows direct reconstruction of arbitrarily structured and polarization-multiplexed emission from individual nanodiamonds. Together, these approaches unlock unprecedented degrees of freedom for nanoscale light shaping and provide a promising route toward scalable quantum photonic devices and high-capacity information processing.