Yue Jiang’s research while affiliated with Nanjing University and other places

Metasurface polarization optics, manipulating polarization using metasurfaces composed of subwavelength anisotropic nanostructure array, has enabled a lot of innovative integrated strategies for versatile and on-demand polarization generation, modulation, and detection. Compared with conventional bulky optical elements for polarization control, metasurface polarization optics provides a feasible platform in a subwavelength scale to build ultra-compact and multifunctional polarization devices, greatly shrinking the size of the whole polarized optical system and network. Here, we review the recent progresses of metasurface polarization optics in both classical and quantum regimes, including uniform and spatially varying polarization-manipulating devices. Basic polarization optical elements such as meta-waveplate, meta-polarizer, and resonant meta-devices with polarization singularities provide compact means to generate and modulate uniform polarization beams. Spatial-varying polarization manipulation by employing the pixelation feature of metasurfaces, leading to advanced diffraction and imaging functionalities, such as vectorial holography, classic and quantum polarization imaging, quantum polarization entanglement, quantum interference, and modulation. Substituting conventional polarization optics, metasurface approaches pave the way for on-chip classic or quantum information processing, flourishing advanced applications in displaying, communication, imaging, and computing.

Traditional optical elements, such as waveplates and polarization beam splitters, are essential for quantum state tomography (QST). Yet, their bulky size and heavy weight are prejudicial for miniaturizing quantum information systems. Here, we introduce nondiffractive silicon metasurfaces with high transmission efficiency to replace the traditional optical elements for QST of polarization-entangled states. Two identical silicon metasurfaces are employed, and each metasurface comprises four independent districts on a micrometer scale. The unit cell of each district consists of two silicon nanopillars with different geometrical sizes and orientation angles, and the interference of the scattered waves from the nanopillars leads to a single output beam from the district with a specific polarization state with a transmission efficiency above 92%. When the two-photon polarization-entangled state shines on different districts of two metasurfaces, each photon of the photon pair interacts with the local nanopillars within the district, and the two-photon state is projected onto 16 polarization bases for state reconstruction. We experimentally demonstrate the reconstruction of four input Bell states with high fidelities. This approach significantly reduces the number of conventional optical components in the QST process and is inspiring for advancing quantum information technology.

Photonic quantum information processing relies on operating the quantum state of photons, which usually involves bulky optical components unfavorable for system miniaturization and integration. Here, we report on the transformation and distribution of polarization-entangled photon pairs with multichannel dielectric metasurfaces. The entangled photon pairs interact with metasurface building blocks, where the geometrical-scaling-induced phase gradients are imposed, and are transformed into two-photon entangled states with the desired polarization. Two metasurfaces, each simultaneously distributing polarization-entangled photons to spatially separated multiple channels M (N), may accomplish M×N channels of entanglement distribution and transformation. Experimentally we demonstrate 2×2 and 4×4 distributed entanglement states, including Bell states and superposition of Bell states, with high fidelity and strong polarization correlation. We expect this approach paves the way for future integration of quantum information networks.

Topological photonics offers the possibility of robust transport and efficiency enhancement of information processing. Terahertz (THz) devices, such as waveguides and beam splitters, are prone to reflection loss owing to their sensitivity to defects and lack of robustness against sharp corners. Thus, it is a challenge to reduce backscattering loss at THz frequencies. In this work, we constructed THz photonic topological insulators and experimentally demonstrated robust, topologically protected valley transport in THz photonic crystals. The THz valley photonic crystal (VPC) was composed of metallic cylinders situated in a triangular lattice. By tuning the relevant location of metallic cylinders in the unit cell, mirror symmetry was broken, and the degenerated states were lifted at the K and K’ valleys in the band structure. Consequently, a bandgap of THz VPC was opened, and a nontrivial band structure was created. Based on the calculated band structure, THz field distributions, and valley Berry curvature, we verified the topological phase transition in such type of THz photonic crystals. Further, we showed the emergence of valley-polarized topological edge states between the topologically distinct VPCs. The angle-resolved transmittance measurements identified the bulk bandgap in the band structure of the VPC. The measured time-domain spectra demonstrated the topological transport of valley edge states between distinct VPCs and their robustness against bending and defects. Furthermore, experiments conducted on a topological multi-channel intersectional device revealed the valley-polarized characteristic of the topological edge states. This work provides a unique approach to reduce backscattering loss at the THz regime. It also demonstrates potential high-efficiency THz functional devices such as topologically protected beam splitters, low-loss waveguides, and robust delay lines.