All-optical modulation of quantum states by nonlinear metasurface

Metasurfaces have proven themselves an exotic ability to harness light at nano-scale,being important not only for classical but also for quantum optics.Dynamic manipulation of the quantum states is at the heart of quantum information processing;however,such function has been rarely realized with metasurfaces so far.Here,we report an all-optical dynamic modulation of the photonic quantum states using the nonlinear metasurface.The metasurface consists of a metallic nanostructure combined with a photoisomerizable azo layer.By tuning the plasmonic resonance through optically switching the azo molecules between their binary isomeric states,we have realized dynamic control of transmission efficiencies of orthogonally polarized photons and also the phase delay between them,thereby an entangled state was efficiently controlled.As an illustration,a quantum state distillation has been demonstrated to recover a Bell state from a non-maximally entangled one to that with fidelities higher than 98%.Our work would enrich the functions of the metasurface in the quantum world,from static to dynamic modulation,making the quantum metasurface going practical.

Effect of unbalanced and common losses in quantum photonic integrated circuits

Loss is inevitable for the optical system due to the absorption of materials, scattering caused by the defects, and surface roughness. In quantum optical circuits, the loss can not only reduce the intensity of the signal, but also affect the performance of quantum operations. In this work, we divide losses into unbalanced linear losses and shared common losses, and provide a detailed analysis on how loss affects the integrated linear optical quantum gates. It is found that the orthogonality of eigenmodes and the unitary phase relation of the coupled waveguide modes are destroyed by the loss. As a result, the fidelity of single-and two-qubit operations decreases significantly as the shared loss becomes comparable to the coupling strength. Our results are important for the investigation of large-scale photonic integrated quantum information processes.

Silicon photonic devices for scalable quantum information applications

With high integration density and excellent optical properties, silicon photonics is becoming a promising platform for complete integration and large-scale optical quantum information processing. Scalable quantum information applications need photon generation and detection to be integrated on the same chip, and we have seen that various devices on the silicon photonic chip have been developed for this goal. This paper reviews the relevant research results and state-of-the-art technologies on the silicon photonic chip for scalable quantum applications. Despite the shortcomings, the properties of some components have already met the requirements for further expansion. Furthermore, we point out the challenges ahead and future research directions for on-chip scalable quantum information applications.