单光子高维编码量子计算研究

A major challenge for future practical and scalable quantum computation is to encode high-dimensional vectors. To do so, most previous experimental works on linear optical quantum computation utilized multi-photon encoding technique, which faced lots of problems including high noise and extreme difficulty to realize any unitary operation. These problems can be solved by encoding high-dimensional vectors with different degrees of freedom of single photons. Based on the developed quantum manipulation technology for single photons, this project aims to encode and control arbitrary 4-dimensional vectors with two degrees of freedom of single photons: polarization and orbital angular momentum. With this technique, we will experimentally demonstrate various quantum information processing protocols. Meanwhile, this project also plans to explore the generation and arbitrary unitary operation of 8-dimensional vectors. The techniques to be developed in this project will overcome the difficulties in the multi-photon encoding techniques such as imperfect multi-photon interference and weak interaction between independent photons. Another advantage for this project is to reduce the cost of photon sources. In summary, this project is an effective extension for multi-photon quantum computation and the developed techniques will provide a new route for future practical and scalable quantum computation.

面向实用化、规模化量子计算的一个基本核心问题是对高维向量进行编码。以往的光量子计算实验工作中所采用的均为多光子编码，存在实现难度大、噪声高、无法实现任意幺正操作等问题。本项目基于成熟的单光子量子操作实验技术，通过单光子的极化和轨道角动量的同时操纵，实现对于单光子四维向量的量子态编码与任意幺正操作，并在此基础上将经典高维向量数据编码到单光子量子态上，实验演示若干量子信息处理任务。同时，本项目还将探索进一步结合路径自由度来实现单光子八维向量的量子态编码与任意幺正操作。本项目的研究路线相比多光子编码而言，可以避免多光子干涉不完美和相互作用弱的问题，同时也又可以减少资源消耗，是基于多光子纠缠量子计算研究的有效扩展，为实用化、规模化量子计算提供新的有效途径。

围绕可扩展光量子计算，本项目发展了多项光量子操纵技术，开展了单光子高维编码、调控以及多光子纠缠干涉等多项研究，特别是发展了光子轨道角动量调控技术。在此基础上，同时调控光子的偏振、路径和轨道角动量，利用6光子实现了18比特超纠缠；不断提升用于多光子纠缠干涉的脉冲纠缠源品质，首次实现了10光子纠缠。基于项目组发展起来的国际领先的多种量子纠缠源和相干操纵技术，开展了一系列光量子计算实验研究，取得多项重要研究成果，包括：首次实现基于经典指令的量子云计算演示验证、首次实现突破经典极限的量子指纹识别、首次实现满足保密性条件的量子态三方秘密共享、成功演示了基于嵌入式编码高效量子纠缠测量，首次实现拓扑数据分析（TDA）算法的验证演示、实现可观测量的非局域测量等。综上所述，本项目进一步发展了单光子高维度量子编码技术，实现了经典数据的量子高维向量编码和操作，为下一步发展高维编码的光量子计算奠定了坚实的基础。