The stages of a quantum internet As indispensable as the internet has become in our daily lives, it still has many shortcomings, not least of which is that communication can be intercepted and information stolen. If, however, the internet attained the capability of transmitting quantum information—qubits—many of these security concerns would be addressed. Wehner et al. review what it will take to achieve this so-called quantum internet and propose stages of development that each correspond to increasingly powerful applications. Although a full-blown quantum internet, with functional quantum computers as nodes connected through quantum communication channels, is still some ways away, the first long-range quantum networks are already being planned. Science, this issue p. eaam9288 BACKGROUND The internet has had a revolutionary impact on our world. The vision of a quantum internet is to provide fundamentally new internet technology by enabling quantum communication between any two points on Earth. Such a quantum internet will—in synergy with the “classical” internet that we have today—connect quantum information processors in order to achieve unparalleled capabilities that are provably impossible by using only classical information. As with any radically new technology, it is hard to predict all uses of the future quantum internet. However, several major applications have already been identified, including secure communication, clock synchronization, extending the baseline of telescopes, secure identification, achieving efficient agreement on distributed data, exponential savings in communication, quantum sensor networks, as well as secure access to remote quantum computers in the cloud. Central to all these applications is the ability of a quantum internet to transmit quantum bits (qubits) that are fundamentally different than classical bits. Whereas classical bits can take only two values, 0 or 1, qubits can be in a superposition of being 0 and 1 at the same time. Moreover, qubits can be entangled with each other, leading to correlations over large distances that are much stronger than is possible with classical information. Qubits also cannot be copied, and any attempt to do so can be detected. This feature makes qubits well suited for security applications but at the same time makes the transmission of qubits require radically new concepts and technology. Rapid experimental progress in recent years has brought first rudimentary quantum networks within reach, highlighting the timeliness and need for a unified framework for quantum internet researchers. ADVANCES We define different stages of development toward a full-blown quantum internet. We expect that this classification will be instrumental in guiding and assessing experimental progress as well as stimulating the development of new applications by providing a common language and reference frame for the different scientific and engineering disciplines involved. More advanced stages are distinguished by a larger amount of functionality, thus supporting ever more sophisticated application protocols. For each stage, we describe some of the application protocols that are already known and that can be realized with the functionality provided in that stage. It is conceivable that a simpler protocol, or better theoretical analysis, may be found in the future that solves the same task but is less demanding in terms of functionality. In parallel to the daunting experimental challenges in making quantum internet a reality, there is thus an opportunity for quantum software developers to design protocols that can realize a task in a stage that can be implemented more easily. We identify relevant parameters for each stage to establish a common language between hardware and software developers. Last, we review technological progress in experimental physics, engineering, and computer science that is required to attain such stages. OUTLOOK Building and scaling quantum networks is a formidable endeavor, requiring sustained and concerted efforts in physics, computer science, and engineering to succeed. The proposed stages of development will facilitate interdisciplinary communication by summarizing what we may actually want to achieve and providing guidelines both to protocol design and software development as well as hardware implementations through experimental physics and engineering. Although it is hard to predict what the exact components of a future quantum internet will be, it is likely that we will see the birth of the first multinode quantum networks in the next few years. This development brings the exciting opportunity to test all the ideas and functionalities that so far only exist on paper and may indeed be the dawn of a future large-scale quantum internet. Stages in the development of a quantum internet. Each stage is characterized by an increase in functionality at the expense of greater technological difficulty. This Review provides a clear definition of each stage, including benchmarks and examples of known applications, and provides an overview of the technological progress required to attain these stages. The internet—a vast network that enables simultaneous long-range classical communication—has had a revolutionary impact on our world. The vision of a quantum internet is to fundamentally enhance internet technology by enabling quantum communication between any two points on Earth. Such a quantum internet may operate in parallel to the internet that we have today and connect quantum processors in order to achieve capabilities that are provably impossible by using only classical means. Here, we propose stages of development toward a full-blown quantum internet and highlight experimental and theoretical progress needed to attain them.

中文翻译：

---

量子互联网：未来之路的愿景

量子互联网的发展阶段 互联网已经成为我们日常生活中不可或缺的一部分，但它仍然存在许多缺点，其中最重要的是通信可以被拦截，信息可以被窃取。然而，如果互联网获得了传输量子信息——量子比特的能力——其中许多安全问题将得到解决。韦纳等人。回顾实现这个所谓的量子互联网需要什么，并提出与日益强大的应用程序相对应的发展阶段。尽管以功能性量子计算机作为通过量子通信通道连接的节点的成熟量子互联网还有很长的路要走，但第一个远程量子网络已经在规划中。科学，这个问题 p。eaam9288 背景 互联网对我们的世界产生了革命性的影响。量子互联网的愿景是通过实现地球上任意两点之间的量子通信来提供全新的互联网技术。这样的量子互联网将——与我们今天拥有的“经典”互联网协同作用——连接量子信息处理器，以实现仅使用经典信息不可能实现的无与伦比的能力。与任何全新的技术一样，很难预测未来量子互联网的所有用途。然而，已经确定了几个主要应用，包括安全通信、时钟同步、扩展望远镜基线、安全识别、实现分布式数据的高效协议、通信的指数节省、量子传感器网络以及对远程量子的安全访问。云中的计算机。所有这些应用的核心是量子互联网传输与经典位根本不同的量子位（qubit）的能力。经典位只能取两个值，0 或 1，而量子位可以同时处于 0 和 1 的叠加状态。此外，量子比特可以相互纠缠，导致远距离相关性比经典信息强得多。量子位也不能被复制，任何这样做的尝试都可以被检测到。这一特性使量子比特非常适合安全应用，但同时也使量子比特的传输需要全新的概念和技术。近年来的快速实验进展使第一个基本的量子网络触手可及，强调量子互联网研究人员统一框架的及时性和必要性。进展我们定义了走向成熟量子互联网的不同发展阶段。我们预计这种分类将有助于指导和评估实验进展，并通过为所涉及的不同科学和工程学科提供通用语言和参考框架来刺激新应用程序的开发。更高级的阶段以更多的功能为特色，从而支持更复杂的应用协议。对于每个阶段，我们描述了一些已知的应用协议，并且可以通过该阶段提供的功能来实现。可以想象，一个更简单的协议，或者更好的理论分析，将来可能会发现可以解决相同的任务，但对功能的要求较低。与使量子互联网成为现实的艰巨实验挑战并行，因此量子软件开发人员有机会设计可以在更容易实现的阶段实现任务的协议。我们确定每个阶段的相关参数，以在硬件和软件开发人员之间建立通用语言。最后，我们回顾了达到这些阶段所需的实验物理、工程和计算机科学的技术进步。前景构建和扩展量子网络是一项艰巨的任务，需要在物理学、计算机科学和工程学方面持续和协同努力才能取得成功。拟议的开发阶段将通过总结我们可能真正想要实现的目标，并通过实验物理和工程为协议设计和软件开发以及硬件实现提供指导，从而促进跨学科交流。尽管很难预测未来量子互联网的确切组成部分是什么，但我们很可能会在未来几年内看到第一个多节点量子网络的诞生。这一发展带来了令人兴奋的机会，可以测试迄今为止仅存在于纸上的所有想法和功能，并且可能确实是未来大规模量子互联网的曙光。量子互联网发展的阶段。每个阶段的特点是功能增加，但技术难度更大。本审查提供了每个阶段的明确定义，包括已知应用的基准和示例，并概述了实现这些阶段所需的技术进步。互联网——一个能够同时进行远程经典通信的庞大网络——对我们的世界产生了革命性的影响。量子互联网的愿景是通过实现地球上任意两点之间的量子通信，从根本上增强互联网技术。这样的量子互联网可能与我们今天拥有的互联网并行运行，并连接量子处理器，以实现仅使用经典方法不可能实现的功能。在这里，我们提出了成熟量子互联网的发展阶段，并强调了实现这些阶段所需的实验和理论进展。