We propose a coherent control network for arbitrary polarization states and phases. The network is based on a rotationally symmetric stacked metasurface structure that enables XOR, AND, and OR logic operations across dual communication bands via all-optical phase modulation. Stack rotational symmetry gives the structure a polarization-independent response at two-beam incidence, while the coherent control network can precisely modulate the resonant absorption effect between the incident polarization and the metasurface through phase manipulation. Here, we apply this specialized metasurface to a quantum key distribution (QKD) system and successfully design a hybrid encoding mode that utilizes three optical dimensions-polarization, phase, and wavelength. This allows Alice and Bob to modulate 20 polarization states, increasing the information capacity by a factor of 5 compared to the traditional BB84 protocol. Our research significantly improves the performance of metasurfaces in arbitrary polarization multiplexing and phase manipulation and broadens the information dimension of the QKD system in polarization optics.
We propose a coherent control network for arbitrary polarization states and phases. The network is based on a rotationally symmetric stacked metasurface structure that enables XOR, AND, and OR logic operations across dual communication bands via all-optical phase modulation. Stack rotational symmetry gives the structure a polarization-independent response at two-beam incidence, while the coherent control network can precisely modulate the resonant absorption effect between the incident polarization and the metasurface through phase manipulation. Here, we apply this specialized metasurface to a quantum key distribution (QKD) system and successfully design a hybrid encoding mode that utilizes three optical dimensions-polarization, phase, and wavelength. This allows Alice and Bob to modulate 20 polarization states, increasing the information capacity by a factor of 5 compared to the traditional BB84 protocol. Our research significantly improves the performance of metasurfaces in arbitrary polarization multiplexing and phase manipulation and broadens the information dimension of the QKD system in polarization optics.
Metasurfaces showcase unique abilities to arbitrarily manipulate the amplitude, phase, and polarization of electromagnetic (EM) waves, facilitating their application in wireless communication. In the propagation of EM waves, traditional methods cause severe security concerns in channel/deciphering under eavesdropping. Fortunately, quantum communication, based on quantum key distribution (QKD) of the BB84 protocol, endows the transmission with high security. However, the conventional QKD technology relies on complicated manipulation of a single photon and is prone to channel collapses once an eavesdropper intervenes. Furthermore, the merit of the BB84 protocol has not been realized in metasurfaces as a transmission channel. Here, we, for the first time as far as we know, used metasurfaces to implement wireless transmission of quantum information via the first QKD protocol, BB84. These metasurfaces provided four conjugated quantum states to concretely demonstrate the BB84 protocol through a conveyor-type switching method. High-fidelity holographic results were obtained at ∼10 GHz and beyond in both experiment and simulation. As compared with traditional QKD technology, our BB84 protocol based on metasurfaces is more stable and secure in information transmission. In addition, the metasurfaces have electromechanical switchable mode, empowering them to have multidisciplinary functions in wireless communication, e.g., program-controlled antennas, intelligent reflectors, and variable metalens.
Polarization modulation plays an important role in polarization encoding in quantum key distribution. By using polarization modulation, quantum key distribution systems become more compact and more vulnerable as one laser source is used instead of using multiple laser sources that may cause side-channel attacks. Metasurfaces with their exceptional optical properties have led to the development of versatile ultrathin optical devices. They are made up of planar arrays of resonant or nearly resonant subwavelength pieces and provide complete control over reflected and transmitted electromagnetic waves opening several possibilities for the development of innovative optical components. In this work, the Si nanowire metasurface grating polarizer is designed by COMSOL Multiphysics Software to operate in the visible region and transmit the transverse magnetic polarization of light. The same structure can be rotated by different angles, i.e., 90o, 45o, and -45o to mimic the function of polarization modulation in quantum key distribution systems. The designed structure has an extinction ratio of ~ 60000 and a wide angular tolerance range of (-20o - 20o).
Multiprotocol quantum key distribution (mQKD) enables users to flexibly select protocols for secure quantum communication, though achieving mQKD introduces considerable system complexity and resource demands. Here, we report the first realization of mQKD using a metasurface, which generates multiple hybrid states of photonic spin angular momentum (SAM) and orbital angular momentum (OAM) and distributes them to different users. The incident polarization-entangled photon pair interacts with the metasurface, producing four SAM-OAM hybrid states with high fidelity through spin-orbit conversion. Among these hybrid states, two execute the BB84 protocol, while the other two perform the BBM92 protocol, all demonstrating high secret key rates and low quantum bit error rates. This approach provides a robust, compact solution for generating and distributing SAM-OAM hybrid states and stands out for the remarkable capability of a metasurface in secured information processing.
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.
Abstract Metasurfaces utilize engineered nanostructures to achieve control on all possible dimensions of light, encouraging versatile applications, including beam steering, multifunctional lensing, and multiplexed holograms. Towards the quantum optical regime for metasurfaces, although significant efforts have been put into generating and analyzing specific quantum states, control schemes to further manipulate these quantum states or information are still limited. Here, based on a metasurface, we propose and experimentally demonstrate a continuous heralding scheme to remotely control a vortex beam with high robustness to noise using polarization-entangled photon pairs. Our metasurface entangles polarization and orbital angular momentum (OAM) and the polarization selection on heralding photon erases the which-OAM information on signal photon. It induces an interference of two different OAM states remotely, manifesting a continuous orbital rotation. Our results show that metasurfaces have potential applications in quantum communication and information processing in entangling information with increasing complexity in the content.
Metasurfaces present novel prospects for compacted quantum technologies by providing precise manipulation of amplitude, phase, and polarization of the incident light. Utilizing the advanced polarization control and multiplexing capabilities of metasurfaces, the capacity for detecting and processing quantum information can be enhanced. In this work, we optimize metasurface fabrication using electron-beam lithography and develop a custom SEM image recognition program for precise structure assessment and improved imaging quality. We achieve holographic imaging under quantum state incidence, enabling the reconstruction of quantum state information from the resulting meta-holography.