光子角动量解耦脉冲的物理实现研究

Photon angular momentums, including spin angular momentum (SAM) and orbital angular momentum (OAM), have many promising applications in quantum communication. However, since photons always couple with the external environment in propagation, the coherence of the photons will be degraded during this process. Therefore, photon decoherence has been a major obstacle for quantum communication. For the solid-state quantum systems, researchers have achieved great success in developing dynamical decoupling techniques to suppress decoherence. The basic "component" of the dynamical decoupling is decoupling pulse. Our project will apply the idea of dynamical decoupling to suppress photonic decoherence. To achieve dynamical decoupling for the photons, we need to physically construct decoupling pulses which is suitable for photons. We plan to investigate the physical realization of decoupling pulses for both SAM and OAM, and optimize the experimental error. For OAM, we first achieve any unitary operator on 1-order Laguerre-Gaussian mode poincare, then we design a mode converter, according to optic principle of cylinder lens, to realize the decoupling pulse. For SAM, the impact due to the error of system is analysed and a scheme will be designed to reduce the impact. Our project will deepen the understanding of photon orbital angular momentum with the multi-level nature, as well as provide the theoretical and technical supports for the potential application in quantum communication.

光子（自旋及轨道）角动量在量子通信中具有广泛的应用前景，但光子在传输过程中，与外界环境总存在耦合，导致光子发生退相干，成为光量子通信的重要障碍。动态解耦技术在固态量子系统中成功地抑制了系统退相干，它的基本"部件"是解耦脉冲。本项目计划用玻片、柱面透镜等光学元件构造出适用于光子角动量的解耦脉冲，从而达到在光子系统中运用动态解耦抑制退相干的目的。分别在光子轨道和自旋两个自由度中，研究解耦脉冲的物理实现，并针对实验误差进行优化。在光子轨道角动量自由度中，利用模式转换器等元件实现对1阶拉盖尔-高斯模Poincare球的任意么正变换。在此基础上，根据光学设计原理设计出适用于抑制光子轨道角动量退相干的模式转换器。在光子自旋角动量自由度中，分析由玻片组成的解耦脉冲由于实验误差而引入的影响，并设计减少影响的方案。本项目为拓展光子角动量在未来量子通信等领域中的潜在应用提供理论和技术支持。

光子是量子信息的载体之一，项目在理论方面，研究了利用光子几何相位调控光子的自旋角动量、轨道角动量；在实验上，实现了几何相位对偏振光、涡旋光的调控。分别在光子轨道和自旋两个自由度中，研究解耦脉冲的物理实现，在光子轨道角动量自由度中，利用偏振状态的几何相位实现对1阶拉盖尔-高斯模Poincare球某一方向的幺正变换。本项目为拓展光子角动量在未来量子通信等领域中的潜在应用提供理论和技术支持。

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