量子信息和量子技术白皮书 （合肥宣言）
编者按
在新一轮科技革命和产业变革孕育兴起，特别是第二轮量子革命正向我们走来的时代背景下，2019年9月15日至20日，新兴量子技术国际会议在合肥成功举行。多名诺贝尔物理学奖、沃尔夫物理学奖、狄拉克奖、香农奖、墨子量子奖获奖者，包括发明大数分解算法和量子纠错编码的Peter Shor教授，提出可扩展量子计算、量子模拟和量子中继物理实现方法的Ignacio Cirac教授和Peter Zoller教授，在囚禁离子物理体系量子计算实验领域做出先驱性卓越贡献的David Wineland教授和Rainer Blatt教授，提出量子密码协议、量子隐形传态、纠缠交换以及纠缠纯化理论方案的Charles Bennett教授、Gilles Brassard教授和Artur Ekert教授，完成多光子纠缠和干涉以及自由空间量子传输多项开创性实验、使现实安全的广域量子通信成为可能的潘建伟教授和Anton Zeilinger教授等分别做了大会报告。与会专家一致认为，量子力学的诞生对20世纪人类的生产力产生了决定性的影响，以量子通信、量子计算、量子精密测量为代表的新兴量子信息技术正在全世界范围蓬勃发展，将对21世纪产生深远的影响。科学技术是世界性的、时代性的，各国科学家倡议发展量子科学技术要具有全球视野，加强基础科研领域的国际合作，聚四海之气、借八方之力。为了促进量子信息技术领域的健康发展，会议组委会在广泛咨询国际顾问委员会和程序委员会的基础上，对量子通信、量子计算等领域的发展目标、路径以及趋势等进行了讨论并达成了共识，形成了量子信息和量子技术白皮书（合肥宣言），在此分享给社会公众，以更好地了解量子信息技术的基本原理、发展现状、国际共识和发展前景等相关内容。
中文版
概述
上世纪初量子力学的建立是人类历史上最重大的科学革命之一，催生了半导体、激光、核能、超导、核磁共振、和全球卫星定位系统等重大技术的发明，推动人类在信息、能源、材料和生命等科学领域获得了空前的发展，已经从根本上改变了人类的生活方式和社会面貌，促进了物质文明的巨大进步。自上世纪九十年代以来，量子调控技术的巨大进步使得人类可以对微观粒子的量子状态进行主动的精确操纵，从而诞生了以量子信息技术为代表的这一新兴的领域。量子信息技术，包括量子通信、量子计算、量子精密测量等，可以在确保信息安全、提高运算速度、提升测量精度等方面突破经典技术的瓶颈。鉴于此，2019年9月15日至20日，新兴量子技术国际会议the International Conference on Emerging Quantum Technology (ICEQT2019)在合肥召开，来自中国、美国、英国、法国、俄罗斯、德国、奥地利、瑞士、澳大利亚、加拿大等国的著名研究机构和大学的包括多名诺贝尔物理学奖获得者、沃尔夫物理学奖获得者在内的约500余位专家参会。与会学者讨论了量子信息技术的发展与未来，并达成一系列共识，现总结如下。
量子通信
量子通信是量子信息科学的重要分支，它是指利用量子比特作为信息载体来进行信息交互的通信技术。量子通信有两种最典型的应用方式：量子密钥分发和量子隐形传态。量子密钥分发可以提供原理上无条件安全的通信手段，是首个从实验室走向实际应用的量子信息技术。量子隐形传态可以用来传输任意未知的量子态，同时也是是远距离量子密钥分发所需的量子中继的重要环节。
量子通信是迄今唯一的安全性得到严格证明的通信方式。量子通信的无条件安全是指，在量子密钥传输过程中，窃听者无法做到既偷看又不留下痕迹，这是由量子力学基本原理保证的。在全球学术界三十余年的共同努力下，目前，结合“测量器件无关量子密钥分发”技术和经过精确标定、自主可控光源的量子通信系统已经可以提供现实条件下的安全性。
量子通信不是要替代经典通信方式，而是通过在经典通信中使用量子密钥以提升通信安全性，同时量子通信的规模化应用也需要与经典通信技术相融合。发展量子通信技术的终极目标是构建广域量子通信网络体系，广泛认可的发展路线是：通过光纤实现城域范围内的量子通信网络，通过中继分段传输实现城际量子通信网络，通过卫星中转实现数千公里甚至是全球化的量子通信。
在目前技术条件下，国际上广泛采用可信中继作为实现远距离量子通信的阶段性解决方案，同时积极发展量子中继技术为下一阶段做准备。量子卫星作为自由空间可信中继，也得到了高度重视和积极推进。当前，在中国量子保密通信“京沪干线”和“墨子号”量子卫星的带动下，包括美国、欧洲在内的世界主要国家和地区也纷纷部署建设远距离光纤量子网络，并提出量子卫星计划。在可见的未来，通过卫星和地面光纤网络形成天地一体的广域量子通信网络具有高度的可行性。
量子保密通信京沪干线
量子通信技术的规模化应用还需要在现实条件下安全性测评的基础上，构建标准体系。目前，国际电信联盟（ITU）在上海首次召开量子信息技术国际研讨会并围绕量子通信标准化进行专题讨论，中国提出制定量子密码安全的国际评估标准的构想已经获得国际标准化组织（ISO）批准、欧洲电信标准化协会（ETSI）等也正在开展QKD有关的标准化工作。
“墨子号”实现千公里级星地双向量子纠缠分发
量子计算
实现通用量子计算机需要满足基本的DiVincenzo条件，包括：（1）可定义量子比特，（2）量子比特有足够的相干时间，（3）量子比特可以初始化，（4）可以实现通用的量子门集合，（5）量子比特可以被读出。实现大规模的量子计算机，以上基本量子操作需要超过特定的容错阈值，并通过构建量子逻辑比特进行可扩展的容错量子计算。目前通用量子计算机的实现，除了基于量子门线路的方法，还包括基于哈密顿量的绝热量子计算，及拓扑量子计算等，它们的计算能力是相互等价的。
谷歌量子计算机处理器Sycamore
在达到通用量子计算所需的量子比特数目、量子容错界限等方面的技术要求之前，可以实现专用的量子模拟器，即用可控的量子系统去模拟真实的多体量子系统，这在实现难度上低于通用量子计算机。专用量子模拟器可以解决经典计算机无法胜任的、物理机制尚不清楚的若干重要量子多体问题，包括凝聚态物理、高能物理以及材料科学、化学等学科的多个核心难题，探索其中蕴含的微观机制。
要构建一台真正具有通用计算能力的量子计算机，仍需要长期的努力。与会专家一致认为，为了领域的健康长期发展，除了要在基础研究领域做好操纵精度、可容错之外，规模化、实用性的量子计算研究可以沿如下路线开展。第一个阶段是实现“量子优越性”或称“量子称霸”，即量子模拟机针对特定问题的计算能力超越经典超级计算机，这一阶段性目标可在近期实现；第二个阶段是实现具有应用价值的专用量子模拟系统，可在组合优化、量子化学、机器学习等方面发挥效用；第三个阶段是实现可编程的通用量子计算机，能在经典密码破解、大数据搜索、人工智能等方面发挥巨大作用。实现通用可编程量子计算机还需要全世界学术界的长期艰苦努力。
光量子计算机原型机示意图
目前，国际上正在探索的量子计算的物理系统包括离子阱、超导量子线路、超冷原子、极化分子、线性光学、金刚石色心、硅28中的电子或核自旋等。
量子精密测量
鉴于量子调控与量子信息技术的快速发展，正如2018年第26届国际计量大会上通过的关于用量子化方法定义国际单位制的决议，计量标准将进入“量子时代”。这将全面提高七个基本物理量（长度、质量、时间、电流、温度、物质的量和发光强度）的测量精度，并可广泛用于授时、导航、医学检测、乃至包括引力波探测在内的基础物理检验。
得益于量子效应，量子精密测量能在诸如时间、重力、磁场、成像、遥感等领域，提供比现有技术更高的测量灵敏度、精度和速度。例如，利用超稳激光和光晶格技术实现的高精度光原子钟、采用超稳频率梳的精准时频传输、借助于原子态量子叠加性实现的高灵敏度原子干涉仪、利用高灵敏探测或纠缠光量子态实现的量子成像和遥感、在量子标准下实现测量的固态人造量子传感器等。量子精密测量技术将在下一代时间基准、精确导航、基本物理常数测量、粒子探测、核磁共振成像、远程目标识别、全球地形测绘、引力波或暗物质的感应探测等广泛领域发挥重要作用。
随着物联网的发展，对量子精密测量的需求也日益攀升，也为具备更卓绝性能的量子传感器全面超越现有经典技术提供了良机。与会专家一致认为，此领域应该进一步努力发展包含超稳激光和频率梳、超冷原子、纠缠/单光子、金刚石色心、超导量子器件等多种精密测量技术，以期在未来实现更高性能的量子精密测量。
促进国际合作
量子信息的蓬勃发展源于量子力学的好奇心驱动和基础研究，并在不断地推动和扩展这一领域。同时，在量子信息方面发展的日益先进的技术，反过来，也为探索量子力学新的物理前沿提供了新的工具。显然，在新兴量子技术的每一个阶段，都需要强调基础研究的重要性。
如同上一世纪的量子革命一样，第二次量子革命也必将带来人类物质文明的巨大飞跃。鉴于这些新兴的前沿科技将给整个人类社会带来福祉，与会专家一致认为，在未来的历史长河中，推进量子信息技术的发展是全球学术界的共同责任，建立全球性的合作来共同推动该领域的发展是必要的，而不应该各自关起门研究。为此，应加强不同国家间科学家的合作与交流，在基础研究和共性技术方面尤为如此。
English version
Introduction
The establishment of quantum mechanics at the beginning of the last century is one of the most important intellectual revolutions in human history. It gave birth to major modern technologies such as semiconductors, lasers, and global positioning systems, which promoted an unprecedented development of human society. It has fundamentally changed our lives, the whole society, and promoted the tremendous progress of material civilization. In past decades, profound progress, made both in our understanding of exploiting quantum superposition and entanglement for new ways of information processing and in the experimental methods of coherent control and interaction of individual quantum particles, has given birth to an emerging field of quantum technologies, including but not limited to quantum communication, quantum computing, and quantum metrology. The emerging quantum technology has been driving and enabling a new generation of classically impossible tasks ranging from unconditionally secure quantum communications, breathtakingly powerful quantum simulation and quantum computation, to extremely sensitive measurements. In view of this trend, from 15th to 20th September, 2019, the International Conference on Emerging Quantum Technology (ICEQT2019) was held in Hefei, China. More than 500 experts of research institutes and universities from Austria, Australia, Canada, China, France, Germany, Russia, Switzerland, United Kingdom, United States, etc., participated the conference. The development and the future of quantum information technology were intensively discussed, and the views are summarized in the following.
Quantum communication
Quantum communication, an important branch of quantum information science, is the art of controlling quantum states for transferring information from one place to another. Typical tasks in quantum communication include quantum key distribution (QKD) and quantum teleportation. QKD provides an in principle unconditional security in communication, and is likely the first quantum information technology emerging from laboratories and entering real-life applications. Quantum teleportation can transfer arbitrary an unknown quantum state from one location to another, and plays an important role in quantum repeaters that are required in long-distance QKD.
After three decades of joint efforts from the global academic community, combining measurement-device-independent QKD and self-calibrated home-made sources, practical QKD systems can provide sufficient security under realistic conditions.
QKD is not intended to completely replace the classical communication infrastructures, but rather to complement existing classical cryptographic schemes. At the same time, scalable applications of quantum communication need hybrids with classical communication technologies. To build a global-scale secure QKD network, which is the ultimate goal of the field, a feasible route is to use optical fibers to connect metropolitan QKD networks, using trusted relays (currently) and/or quantum repeaters (future) to link intercity networks, and using satellites to establish long-haul QKD networks.
Practical long-distance QKD implemented by trusted relays is a viable solution adopted worldwide based on the current technology. A satellite can also be used as a relay in free-space QKD, which has been demonstrated and will be promoted further. Encouraged by China's large-scale quantum-based secure communications, especially the Beijing-Shanghai backbone network and the Micius satellite, similar efforts are being undertaken by many other countries which have started long-distance QKD projects and proposed quantum satellite initiatives. In the foreseeable future, a space-ground wide-area quantum communication network that integrates through satellite and terrestrial fiber networks is feasible.
The large-scale and commercial applications of QKD require the field to establish standards based on safety assessments under realistic conditions. The International Telecommunication Union (ITU) held its first international conference on quantum information technology in Shanghai in 2019 with emphasize on standardization of quantum communication. China's proposal to develop an international standard for quantum cryptography has been approved by the International Organization for Standardization (ISO). The European Telecommunications Standards Institute (ETSI), along with others, are also promoting QKD-related standardization.
Quantum computation
Quantum computing is a new computing paradigm that harnesses properties of quantum mechanics such as quantum superposition and interference for enhanced methods of computation. This can provide exponential speedups over classical computers for some problems, providing solutions for several hard large-scale problems. Both the universal quantum computer and a special-purpose quantum simulator are generally referred to as a quantum computer.
Universal quantum computers must meet five basic DiVincenzo criteria: (1) well-defined qubits, (2) long coherence time, (3) qubits can be initialized, (4) universal quantum gates can be implemented, and (5) qubits can be read out. The precision of the quantum gates is required to surpass certain thresholds for scalable fault-tolerant quantum computing with quantum error correction. In addition to the gate-based model, universal quantum computing also has other equivalent approaches: adiabatic quantum computation and topological quantum computation.
Universal quantum computing still faces stringent technical requirements, such as reaching the fault tolerance threshold and the required large number of qubits. Special-purpose quantum simulators use well-controlled quantum systems, and is expected to be easier to realize than universal quantum computers. Quantum simulators can be useful in various fields such as condensed-matter physics, materials science, and quantum chemistry, to efficiently solve the relevant many-body problems that otherwise cannot be simulated by classical computers.
Given that building a universal quantum computer still requires long-term efforts, the scientists in ICEQT agreed that in order to maintain a healthy and smooth development of the field, a feasible step-by-step roadmap could be as follows. The first stage is to demonstrate "quantum advantage", that is, showing that quantum processors can surpass the performance of classical supercomputers on certain problems. This goal is expected to soon be achieved. The second step is to realize quantum simulators with non-trivial applications such as optimization, quantum chemistry, machine learning. The final and most challenging stage is building programmable universal quantum computers, which could have high impact in cracking classical encryption systems, big-data-set searches, and artificial intelligence.
Research groups from all over the world are attempting various physical systems for quantum computing, such as ion traps, superconducting circuits, ultracold atoms, polar molecules, photons, color centers, and quantum dots.
Quantum metrology
With the rapid development of quantum control and quantum information technology, the metrology standards will enter the "quantum era", as marked by the 26th General Conference of Weights and Measures in 2018 (CGPM2018) on the new definition of the International System of Units by means of quantum.
By harnessing quantum effects, quantum sensing and metrology can offer higher sensitivity, accuracy and speed of use than current technologies, particularly for timing, gravity, magnetic and imaging fields. For instance, optical atomic clocks leverage advances in ultra-stable lasers and optical lattices to achieve a high-precision time standard; time-frequency transfer explores ultra-stable frequency combs to distribute accurate time and stable frequency between remote locations; atomic interferometers use quantum superpositions of atomic states to measure gravitational acceleration and rotation with extremely high precision; quantum imaging and remote sensing use high-sensitivity detection, entangled or squeezed light to provide higher resolution and sensitivity for imaging and sensing; solid-state artificial quantum sensors can perform precise measurements in quantum standards. Quantum sensing and metrology will play important roles in the next-generation time standards, precision navigation, tests of fundamental constants, particle detection, magnetic resonance imaging, long-range target recognition, satellite-based global topography, sensing of gravitational waves or dark matter and so forth.
The demands for precise quantum sensing and metrology are expanding with the developments of the “Internet of Things,” and there is a great opportunity for quantum sensors to provide enhanced capabilities over classical technologies. The scholars reached the consensus that the research community should keep developing various techniques for superior quantum sensing and metrology, including ultrastable lasers and frequency combs, ultracold atoms, entangled/single photons, nitrogen vacancy centers, superconducting devices and so forth.
International collaborations
The flourishing field of quantum information originated from curiosity-driven and fundamental research in quantum mechanics, which has been continuously driving and expanding the field further. Meanwhile, increasingly advanced technologies developed in quantum information, in return, have provided new tools in probing new physical frontiers in quantum mechanics. It is clear that in every stage of emerging quantum technology, the importance of fundamental research can never be over emphasized. The second quantum revolution will likely provide another huge leap in human civilization. These emerging technologies will bring benefits to the whole human society; the scientists at the ICEQT agreed that it is necessary to establish global collaborations to jointly promote the development of this field in the future. To this end, the collaboration and communication between scientists of different countries should be promoted, especially in the field of basic research and common technologies.
这里是墨子沙龙——中国科学技术大学上海研究院于2016年起开始举办的公益科普论坛，致力于专业、权威、有深度的沙龙科普活动，每月一次，邀请国内外知名科学家为大家讲述科学那些事。关注墨子沙龙，我们在这里等你来。
授权或合作请联系微信号MICIUS-SALON或mozi@ustc.edu.cn，转载微信原创文章可直接后台回复“转载”查看转载说明
相关内容
想要和更多志同道合的人一同讨论科普问题，获得墨子沙龙小秘书贴心服务，及时获取各类科普活动通知吗？扫码加墨子沙龙小秘书，拉你入墨子沙龙超大群。
墨子沙龙是由中国科学技术大学上海研究院主办、上海市浦东新区科学技术协会及中国科大新创校友基金会协办的公益性大型科普论坛。沙龙的科普对象为对科学有浓厚兴趣、热爱科普的普通民众，力图打造具有中学生学力便可以了解当下全球最尖端科学资讯的科普讲坛。
关于“墨子沙龙”