全光量子信息处理器的实验研究

Quantum information science has been developed in the past two decades from a visional idea to one of the most important branches of physics. There are still some key points which are not reachable with the current technology. In this project, we focus on experimental realization of all optical quantum information processing. Experimental research in all optical quantum information processing studies the potential use of quantum mechanical systems--photons--for information-processing tasks such as quantum communication and quantum computing. Quantum communication can offer capacity gains due to pure quantum resources, such as entanglement. We will prepare experimentally multi-photon entanglement which can be used to transmit information. By using multiple entangled photons the noise limit of the information channel can be decreased from the shot noise limit to Heisenberg limit and hence the capacity of the information channel can be increased with the fixed bandwidth. On the other hand, we will experimentally realize entanglement of the orbital angular momentum state of photons which can increase the bandwidth of information channel and hence increase the capacity with the fixed signal-to-noise ratio. For the hardware of quantum computing, we will realize multi-qubit quantum logical gates with linear optical elements. For the software of quantum computing, we will use linear optical elements and fused fiber coupler (or Femtosecond laser direct-writing waveguide array) to demonstrate the Boson sampling computation based on non-interacting and identical photons on randomly designed optical network and realize quantum walk algorithms for searching an unstructured database. In the quantum walk architecture, we can also simulate complex phenomena such as Anderson localization, quantum chaos, and quantum ratchet. On the other hand we will build quantum simulation network and experiment characterisation of a complex system such as quantum phase transition, by means of a photonic quantum simulation set-up. Our research will lead to the integration, practicalization, and industrialization of quantum computing and quantum information processing in the near future.

本项目旨在全光量子信息处理器的实验研究，拟将其应用于量子通信和量子计算两个方面。一方面，针对全光量子通信，本项目将着重于利用量子信息技术提高信道容量的理论和实验研究。具体来说，实验上将信息加载在多光子纠缠态上可极大地压缩信道的信噪比，从而提高信道容量。进而利用光子的轨道角动量拓展信道的带宽，进一步提高信道容量。另一方面，针对全光量子计算，我们将从软件和硬件两个方面进行研究。软件方面结合线性光学体系和集成光纤/波导体系实验实现量子随机行走算法和玻色子采样算法。硬件方面则着重实现普适的多比特量子逻辑门操作。作为一个阶段性中间目标，我们也将利用线性光学系统实现量子模拟平台，通过多光子及高维度纠缠态的制备和调控，模拟在当前实验条件下难以操控和测量的物理系统以及复杂的物理现象，获得对一些未知现象的信息，进一步实现对被模拟体系的研究。上述实验研究取得成功，必将推动量子信息技术的实用化、集成化和产业化。

在项目资助期间，首先实验实现基于全光量子行走的量子信息处理器，并将全光量子信息处理器应用于量子模拟，量子测量及验证量子力学基础原理等方面，取得了一定成就，共在Nature Physics, Physical Review Letters等SCI收录学术期刊上发表高水平学术论文三十六篇，均标注项目资助。研究工作进展顺利，进度符合项目预期计划，超过预期研究成果。取得的主要研究进展和重要结果主要集中在利用全光量子信息处理器验证量子力学基础理论和实现量子模拟两个方面。.1全光量子信息处理器验证量子力学基础理论。项目组首次在实验中观测到非定域性和互文性这两种量子特性之间存在此消彼长的monogamy关系，从而提供直接证据揭示量子纠缠是一种普适的资源。Physical Review Letters刊发了这一项关于量关联的重要进展，并选为Editors' Suggestion。论文一经发表引起了国内外专家同行及媒体的广泛关注，《江苏科技报》以"量子纠缠被证明是普适资源"为题报道了项目组在量子关联实验研究中取得的重要进展。Phys.org报告了项目组关于量子关联的实验进展，并刊发题为Two defining features of quantum mechanics never appear together的feature story。.2全光量子信息处离去实现量子模拟。团队首次在开放系统中实验实现宇称-时间对称的量子行走并观测到新型一维拓扑保护边界态，为基于量子行走平台实现量子计算提供了新的依据。该研究成果以长文（article）形式发表于Nature Physics。这篇论文涵盖了宇称-时间对称，量子行走，拓扑保护边界态三个近年来量子物理学界最为关注的方向。研究成果一经发表引起国内外专家同行及新闻媒体的广泛关注，项目负责人薛鹏教授接受新媒体《知识分子》采访，并刊发《薛鹏团队在量子行走领域取得重要进展|前沿》的文章。中国激光刊发了《薛鹏：在宇称-时间对称中的量子行走》的报道。Phys.org报告了项目组关于宇称-时间守恒的量子行走的实验进展，并刊发题为Unconventional quantum systems may lead to novel optical devices的feature story。并入选“2017年度中国光学十大进展（基础研究类）”。