Explainer: What Is Quantum Communication?

Researchers and companies are creating ultra-secure communication networks that could form the basis of a quantum internet. This is how it works.

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By Martin Giles

Barely a week goes by without reports of some new mega-hack that's exposed huge amounts of sensitive information, from people's credit card details and health records to companies' valuable intellectual property. The threat posed by cyberattacks is forcing governments, militaries, and businesses to explore more secure ways of transmitting information.
几个星期过去了,没有报道一些新的大型黑客暴露了大量的敏感信息,从人们的信用卡详细信息和健康记录到公司宝贵的知识产权。网络攻击带来的威胁迫使政府,军队和企业探索更安全的信息传输方式。

Today, sensitive data is typically encrypted and then sent across fiber-optic cables and other channels together with the digital "keys" needed to decode the information. The data and the keys are sent as classical bits --- a stream of electrical or optical pulses representing
今天,敏感数据通常被加密,然后通过光纤电缆和其他通道与解码信息所需的数字"密钥"一起发送。数据和密钥作为经典位发送 - 表示电脉冲或光脉冲流 1 s and
s and 0 s. And that makes them vulnerable. Smart hackers can read and copy bits in transit without leaving a trace.
秒。这使他们变得脆弱。聪明的黑客可以在传输过程中读取和复制位而不会留下痕迹。

Quantum communication takes advantage of the laws of quantum physics to protect data. These laws allow particles --- typically photons of light for transmitting data along optical cables --- to take on a state of
量子通信利用量子物理定律来保护数据。这些定律允许粒子 - 通常是光子光沿着光缆传输数据 - 呈现出一种状态superposition, which means they can represent multiple combinations of
,这意味着它们可以代表多种组合 1 and
and 0 simultaneously. The particles are known as quantum bits,
同时。这些粒子被称为量子比特,or qubits.
.

The beauty of qubits from a cybersecurity perspective is that if a hacker tries to observe them in transit, their super-fragile quantum state "collapses" to either
从网络安全的角度来看,量子比特的美妙之处在于,如果黑客试图在传输过程中观察它们,那么它们超级脆弱的量子态会"崩溃"到 1 or
or 0 . This means a hacker can't tamper with the qubits without leaving behind a telltale sign of the activity.
。这意味着黑客无法在不留下活动迹象的情况下篡改量子比特。

Some companies have taken advantage of this property to create networks for transmitting highly sensitive data based on a process called quantum key distribution, or QKD. In theory, at least, these networks are ultra-secure.
一些公司利用这个属性创建网络,用于基于称为量子密钥分发或QKD的过程传输高度敏感的数据。理论上,至少,这些网络是超安全的。

What is quantum key distribution?

QKD involves sending encrypted data as classical bits over networks, while the keys to decrypt the information are encoded and transmitted in a quantum state using qubits.
QKD涉及通过网络将加密数据作为经典比特发送,而解密信息的密钥使用量子比特以量子状态进行编码和传输。

Various approaches, or protocols, have been developed for implementing QKD. A widely used one known as BB84 works like this. Imagine two people, Alice and Bob. Alice wants to send data securely to Bob. To do so, she creates an encryption key in the form of qubits whose polarization states represent the individual bit values of the key.
已经开发了用于实现QKD的各种方法或协议。被广泛使用的BB84就是这样的。想象一下两个人,爱丽丝和鲍勃。 Alice希望将数据安全地发送给Bob。为此,她以量子比特的形式创建加密密钥,其极化状态表示密钥的各个比特值。

The qubits can be sent to Bob through a fiber-optic cable. By comparing measurements of the state of a fraction of these qubits --- a process known as "key sifting" --- Alice and Bob can establish that they hold the same key.
量子比特可以通过光纤电缆发送给Bob。通过比较这些量子比特的一部分状态的测量值 - 称为"关键筛选"的过程---爱丽丝和鲍勃可以确定他们持有相同的密钥。

As the qubits travel to their destination, the fragile quantum state of some of them will collapse because of
随着量子比特到达目的地,其中一些脆弱的量子态将因为而崩溃decoherence. To account for this, Alice and Bob next run through a process known as "key distillation," which involves calculating whether the error rate is high enough to suggest that a hacker has tried to intercept the key.
。为了解释这一点,Alice和Bob接下来经历了一个称为"关键蒸馏"的过程,其中涉及计算错误率是否足够高以表明黑客试图拦截密钥。

If it is, they ditch the suspect key and keep generating new ones until they are confident that they share a secure key. Alice can then use hers to encrypt data and send it in classical bits to Bob, who uses his key to decode the information.
如果是的话,他们会丢弃可疑密钥并继续生成新密钥,直到他们确信他们共享一个安全密钥。然后,Alice可以使用她来加密数据并将其以经典位发送给Bob,Bob使用他的密钥对信息进行解码。

We're already starting to see more QKD networks emerge. The longest is in China, which boasts a 2,032-kilometer (1,263-mile) ground link between Beijing and Shanghai. Banks and other financial companies are already using it to transmit data. In the US, a startup called Quantum Xchange has
我们已经开始看到更多的QKD网络出现了。最长的是中国,它拥有北京和上海之间2,032公里(1,263英里)的地面连接。银行和其他金融公司已经在使用它来传输数据。在美国,一家名为Quantum Xchange的初创公司拥有struck a deal giving it access to 500 miles (805 kilometers) of fiber-optic cable running along the East Coast to create a QKD network. The initial leg will link Manhattan with New Jersey, where many banks have large data centers.
允许它访问沿东海岸运行的500英里(805公里)的光纤电缆,以创建QKD网络。最初的一条腿将连接曼哈顿与新泽西州,许多银行都拥有大型数据中心。

Although QKD is relatively secure, it would be even safer if it could count on quantum repeaters.
尽管QKD相对安全,但如果能够依靠量子中继器,它会更安全。

What is a quantum repeater?

Materials in cables can absorb photons, which means they can typically travel for no more than a few tens of kilometers. In a classical network, repeaters at various points along a cable are used to amplify the signal to compensate for this.
电缆中的材料可以吸收光子,这意味着它们通常可以行进不超过几十公里。在传统网络中,沿着电缆的各个点处的中继器用于放大信号以补偿这一点。

QKD networks have come up with a similar solution, creating "trusted nodes" at various points. The Beijing-to-Shanghai network has 32 of them, for instance. At these waystations, quantum keys are decrypted into bits and then reencrypted in a fresh quantum state for their journey to the next node. But this means trusted nodes can't really be trusted: a hacker who breached the nodes' security could copy the bits undetected and thus acquire a key, as could a company or government running the nodes.
QKD网络提出了类似的解决方案,在各个点创建"可信节点"。例如,北京到上海的网络有32个。在这些路径上,量子密钥被解密成比特,然后以新的量子状态重新加密,以便到达下一个节点。但这意味着受信任的节点实际上不可信任:违反节点安全性的黑客可以复制未检测到的位,从而获取密钥,运行节点的公司或政府也可以。

Ideally, we need quantum repeaters, or waystations with quantum processors in them that would allow encryption keys to remain in quantum form as they are amplified and sent over long distances. Researchers have demonstrated it's possible in principle to build such repeaters, but they haven't yet been able to produce a working prototype.
理想情况下,我们需要量子中继器或带有量子处理器的路由器,它们允许加密密钥在被放大并长距离发送时保持量子形式。研究人员已经证明原则上可以制造这样的中继器,但他们还没有能够生产出工作原型。

There's another issue with QKD. The underlying data is still transmitted as encrypted bits across conventional networks. This means a hacker who breached a network's defenses could copy the bits undetected, and then use powerful computers to try to crack the key used to encrypt them.
QKD还有另一个问题。基础数据仍然作为传统网络的加密比特传输。这意味着违反网络防御的黑客可以复制未检测到的位,然后使用功能强大的计算机尝试破解用于加密它们的密钥。

The most powerful encryption algorithms are pretty robust, but the risk is big enough to spur some researchers to work on an alternative approach known as quantum teleportation.
最强大的加密算法相当强大,但风险足以刺激一些研究人员开发一种称为量子隐形传态的替代方法。

What is quantum teleportation?

This may sound like science fiction, but it's a real method that involves transmitting data wholly in quantum form. The approach relies on a quantum phenomenon known as
这可能听起来像科幻小说,但它是一种真正的方法,涉及完全以量子形式传输数据。该方法依赖于称为量子现象的量子现象entanglement.
.

Quantum teleportation works by creating pairs of entangled photons and then sending one of each pair to the sender of data and the other to a recipient. When Alice receives her entangled photon, she lets it interact with a "memory qubit" that holds the data she wants to transmit to Bob. This interaction changes the state of her photon, and because it is entangled with Bob's, the interaction instantaneously changes the state of his photon too.
量子隐形传态通过创建成对的纠缠光子然后将每对中的一对发送给数据发送者而将另一对发送给接收者来工作。当爱丽丝收到她纠缠的光子时,她让它与一个"记忆量子位"相互作用,该记忆量子点包含她想要传送给鲍勃的数据。这种相互作用改变了她的光子状态,因为它与鲍勃的光子纠缠在一起,这种相互作用也瞬间改变了他的光子状态。

In effect, this "teleports" the data in Alice's memory qubit from her photon to Bob's. The graphic below lays out the process in a little more detail:
实际上,这将爱丽丝的记忆量子位中的数据从她的光子"传送"到鲍勃的。下图更详细地介绍了该过程:

Researchers in the US, China,
美国,中国的研究人员,and Europe are racing to create teleportation networks capable of distributing entangled photons. But getting them to scale will be a massive scientific and engineering challenge. The many hurdles include finding reliable ways of churning out lots of linked photons on demand, and maintaining their entanglement over very long distances --- something that quantum repeaters would make easier.
正在竞相创造能够分布纠缠光子的传送网络。但要让它们扩大规模将是一项巨大的科学和工程挑战。许多障碍包括找到可靠的方法来按需生成大量连接的光子,并保持它们在很长距离内的纠缠 - 这是量子中继器更容易实现的。

Still, these challenges haven't stopped researchers from dreaming of a future quantum internet.
尽管如此,这些挑战并没有阻止研究人员梦想未来的量子互联网。

What is a quantum internet?

Just like the traditional internet, this would be a globe-spanning network of networks. The big difference is that the underlying communications networks would be quantum ones.
就像传统的互联网一样,这将是一个跨越全球的网络网络。最大的区别在于底层通信网络将是量子通信网络。

It isn't going to replace the internet as we know it today. Cat photos, music videos, and a great deal of non-sensitive business information will still move around in the form of classical bits. But a quantum internet will appeal to organizations that need to keep particularly valuable data secure. It could also be an ideal way to connect information flowing between
它不会像我们今天所知的那样取代互联网。猫照片,音乐视频和大量非敏感商业信息仍将以经典的形式移动。但量子互联网将吸引那些需要保护特别有价值数据的组织。它也可以是连接信息之间的理想方式quantum computers, which are increasingly being made available through the computing cloud.
,越来越多地通过计算云提供。

China is in the vanguard of the push toward a quantum internet. It launched a dedicated quantum communications satellite called Micius a few years ago, and in 2017 the satellite helped stage the world's first intercontinental, QKD-secured video conference, between Beijing and Vienna. A ground station already links the satellite to the Beijing-to-Shanghai terrestrial network. China plans to launch more quantum satellites, and several cities in the country are laying plans for municipal QKD networks.
对量子互联网的推动。它几年前发射了一颗名为Micius的专用量子通信卫星,并于2017年在北京和维也纳之间帮助举办了世界上第一个洲际QKD安全视频会议。地面站已经将卫星连接到北京到上海的地面网络。中国计划发射更多的量子卫星,该国的几个城市正在为市级QKD网络制定计划。

Some researchers
Some researchers have warned that even a fully quantum internet may ultimately become vulnerable to new attacks that are themselves quantum based. But faced with the hacking onslaught that plagues today's internet, businesses, governments, and the military are going to keep exploring the tantalizing prospect of a more secure quantum alternative.
甚至全量子互联网也可能最终容易受到基于量子的新攻击的攻击。但面对困扰当今互联网的黑客冲击,企业,政府和军方将继续探索更加安全的量子替代品的诱人前景。

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