量子网络：下一代安全计算

继我的第一篇关于量子计算机的文章之后，我现在探索并尝试解释同样奇妙而又充满挑战的量子网络世界。量子计算带来了量子网络，而我们拥有的最好的技术就是光纤。尽管量子计算机接近绝对的魔力，但它们仍然需要网络进行通信，而且在大多数情况下，我们不会考虑铜线。光纤是关键，但独自发送微小的光子却是一个奇怪的挑战。即使未来看起来都是量子的，你也可以打赌，未来几年仍将有大量旧技术并行工作，因此确保它们都能共存并保持安全将是系统管理员面临的更大挑战之一。

我们所熟知的互联网

十几岁的时候，我和一些朋友去美国当交换生。在提高英语水平的同时，我们也注意到，通过切换到母语瑞典语，我们可以方便地进行私人交流。我们可以在公共场合说各种废话，但没人能听懂。直到有一天，一位老太太用严厉的眼神看着我们，用完美的瑞典语告诉我们，我们应该为自己感到羞耻，注意自己的语言。我们脸红了，觉得自己很傻，含糊地道歉，然后赶紧离开了。

互联网的情况也类似，大多数时候，我们可以进行私密且安全的对话；但是，这种通信始终存在被拦截的风险。信息可能会被盗用或篡改，因此，安全团队对任何漏洞迹象都严加防范，这是有充分理由的，尤其是当您碰巧接触到备受关注或高价值信息时。

众所周知，互联网上充满了安全协议和加密算法，以保护我们的对话和我们生成的所有数据。但是，邪恶势力猖獗，他们随时有可能解密、窃取、复制、伪造或以其他方式窃取我们的宝贵信息。如果他们无法破解这些信息，他们就会通过释放各种创造性的恶意软件和攻击来淹没通信链路，从而阻止这些信息。

量子计算机的通信方式不同。

[读者还喜欢： 运行快速 NMAP 扫描来清点我的网络]

量子纠缠网络

Quantum entanglement is when two connected particles are placed in different locations, where the sender has one part, and the receiver has the other. The entangled particles will simultaneously adopt the opposite position of the other entangled particle. This way, you immediately know what the other side is doing, and the weird thing is that at this stage, there is no communication to intercept.

At the University of Bristol, a team of international scientists has created a quantum network that, when extended, has "the potential to serve millions of users." This sounds very ambitious, and it is a pretty big deal because, up until now (when this article was written), quantum entangled networks have mostly consisted of just two nodes. Extending them with more nodes is not easy, as it requires a multitude of expensive components that, in turn, call for substantial financial backing. The Bristol team has created a quantum network sporting eight nodes and using eight receiver boxes.

Considering that previous methods would need 56 boxes to care for eight nodes, this is a huge breakthrough. Also, the fact that they are using existing technology is even better, but the challenge is still distance, which I will come to later.

Bye, bye, copper

Information in a quantum network can be transferred in fiber optics, and that is, of course, very good because there is a lot of it around, and more are being rolled out. The quantum state photons that travel along the fiber optics are very sensitive to interference, which means the quantum state is easily lost. The photons are so tiny and weak that, after some distance, they are absorbed into the fiber optic cable. There is much research on how to tackle this challenge, and progress is being made, but so far, only at temperatures around absolute zero.

Not power-hungry

I have already written about quantum computers and said that they are big, bulky, and consume lots of energy. The thing is, that energy is needed to create the special circumstances necessary for the quantum physics to kick in. This includes things like vacuum, temperatures close to absolute zero, and an environment that is absolutely free from interference. The actual photons and electrons that" do quantum" need minuscule amounts of power, so once quantum state can reliably operate at room temperatures, we might see much smaller computers that need very little energy.

Quantum repeaters

As already mentioned, the current fiber optic networks have the annoying knack of absorbing the transmitted photons, and this happens within just a few kilometers. The crux is that the quantum entanglement is a very fragile state, and it is hard to maintain. Even the smallest disturbance or interaction between one of the photons and whatever is around it will break the link—enter repeaters. However, current repeaters have limitations and vulnerabilities and become complex to maintain once you start to scale up.

Passing the baton

A quantum repeater will measure the quantum properties of the arriving photons. The repeater then transfers the quantum properties over to new photons and sends them off on the next leg. Considering there could easily be 100,000 photons per second, the repeater will be a busy place.

This relay process makes it possible to propagate the entanglement over much longer distances, but in my simple world, I just wonder how we can make sure that the correct quantum properties are transferred. Possibly, this is sorted by quantum entanglement, where the recipient already knows what to expect.

If we put this to scale, we are going to need some serious monitoring; not just to track errors but also to correct them. The field of mathematics dedicated to quantum physics and its peculiarities is constantly making progress. In fact, there is so much progress, I have to stop reading research papers, or I will never finish this article. That's how fast things are moving in this area.

Quantum at a distance

A science team at Yokohama National University has developed a new way to entangle photons and has managed to send these photons in excess of 10 kilometers across optical fiber. They have also used a single repeater and, in doing so, achieved a total distance of 20 kilometers.

As of this writing, the farthest anyone has managed to maintain quantum entanglement was 83.7 kilometers, accomplished this year by scientists from the U.S. Department of Energy's Argonne National Laboratory and the University of Chicago. But I am sure we will see that record broken many times over in the near future.

Keeping a secret

The qubits that are transported across the quantum network have a very specific and unique characteristic called" the observer effect," which means they are impossible to interrupt, and this is part of how quantum mechanics work. The observer effect means that any attempt to monitor the photons as they move along the network would not only modify them but actually destroy them.

This means the intended recipient will immediately know if there have been attempts to eavesdrop en route. There is *currently no way around this phenomenon, as it is an inherent property of quantum mechanics—so, it's no surprise that governments, medical companies, and financial institutions are overtly interested.

*Since the research in this area is moving at such a fantastic speed, I wouldn't be surprised if scientists will figure out a way to circumvent this inherent property before you read this.

Encrypted quantum networks

So, how secure can you get? Apparently, not enough. The field of quantum cryptography is booming, and by using the technology of quantum key distribution (QKD), it is possible to encrypt and decrypt information between the sender and receiver. The qubits can only be read once they have arrived at their destination, and you have the correct quantum key to unlock it, so no more eavesdropping.

Quantum nodes in space?

By now, we know that quantum physics works best without any interference, in vacuums where it is very cold, and that makes some parts of space near Earth very suitable. The power that quantum computers need here on Earth mostly goes to create the special conditions that space offers in abundance. The qubit itself needs absolutely minuscule power to operate, so scientists are looking into the opportunity to have quantum computers in satellites entangled with each other, which would allow problems to be sent from Earth, processed in space, and then have the answer/s returned to Earth. The satellites would be sending entangled photons back to Earth—how cool is that.

This is not me completely off my hinges—the idea actually comes from scientists at Louisiana State University in Baton Rouge. Oh, and by the way, quantum entanglement in space has already been successfully tested—in 2017.

More is better

Hummingbird, Eagle, Osprey, and Condor—these are names of processors with an increasing number of qubits from Big Blue (IBM), which is on the path toward a one million-qubit quantum computer, targeted to launch in 2030. You might be surprised to know that, in September 2020, IBM released its new 65-qubit Quantum Hummingbird processor, but only to IBM Q Network members. Either way, you can read more about their roadmap here.

Qubits in perspective

Today's computers work with bits. One bit can be either zero or one. The equivalent in quantum computers is called a "qubit," and it can have the value of both zero and one at the same time, including everything in between. This makes the quantum computer superior in the sense that it does not take too many qubits to outrun the supercomputers we have today. Now, just imagine the performance of a one million qubit computer.

If we are going to have mega quantum computers in just 10 years (or less), we need some serious fiber networks and very clever network components to go with them. Looking at the rate of development in this area, we will need a lot of new tech that is yet to be invented. I believe we are on the verge of a technological super-jump that will be much bigger and more dramatic than anything we have previously experienced.

I am curiously following the companies entering this emerging market. They are leading; who will follow?

Quantum weakness

In my career, I have heard statements about technologies like" 100% secure" or" this is the absolute limit," just to see them broken another six months down the line. "How to achieve unconditional network security thanks quantum mechanics" is probably an equally feeble thought. Threats on the quantum internet are discussed in this document created by Takahiko Satoh, Shota Nagayama, Shigeya Suzuki, Takaaki Matsuo, and Rodney Van Meter. Their focus is on the quantum repeater architecture, and they argue that, since a repeater includes classical computing hardware, the possible attacks are very similar to those on classical systems.

Considering that attacks usually don't target the strongest points—which are the specifics of quantum mechanics—one can reasonably expect attacks on the weakest points, which, inevitably, will be the classical network components.

[ Network getting out of control? Check out Network automation for everyone, a free book from Red Hat. ] 

Wrapping up

With quantum computers come quantum networks, and the best current technology we have for that is fiber optics. Qubits carrying quantum state photons are transferred across the network, and thanks to the nature of quantum mechanics and the" observer effect," the quantum state can not be intercepted during transport. However, there might be weakness in the repeaters—a necessary component if any distance is to be achieved.

Some tech has yet to be engineered, and there are plenty of challenges, but with massive financial interest in a "secure internet," researchers have all the funding they need. The blistering progress in this area becomes obvious if you look at the sheer amount of scientific papers that are being published.

If it can be built, it can be broken. The debate around security and encryption is lively, and I would not expect dark forces to sit idle, waiting for quantum technology to mature.

Quantum computers and networks are already here, and within a few years, they will become commercially available. Will you be ready by then?