The Quantum Internet of the Future




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You’ve just captured the intel and now you have to get it back to the CIA, ASAP. You have the latest encryption, but there’s still a chance the network could be compromised, and there’s no way to know. Do you risk it? This scenario could be from a spy thriller or a video game, but it’s not totally absurd. In fact, scientists across the globe are working on a solution to this very problem. And this week, physicists at Princeton and the Australian National University have made some progress. In a paper published in the journal Nature Physics, they announced that they’re a little closer to making a long-range quantum internet a reality. A quantum what? Alright, we’re going to need to take a step back here. A quantum internet, which would encode information using tiny particles, could be the perfect way to send messages that are completely secure. You’ve probably heard about quantum computing, which uses quantum bits, or qubits, instead of the ones and zeroes our regular computers use. Qubits are special because they’re based on the physical properties of particles, like an electron’s spin. An electron’s spin can be up or down, but because this is quantum mechanics, where everything is complicated and weird to think about, its spin can also be up and down at the same time. That’s what’s known as superposition, where particles like electrons or photons are in two opposite states at once. It makes no sense in the context of how we normally experience the world, but that’s just the tip of the very, very strange quantum mechanical iceberg. On the scale of tiny particles, the classic principles of science start to break down, and things happen that seem like they should be impossible. But based on a lot of experiments and math, we know they are happening. So even though it can be hard to wrap our brains around it, we’ve just had to accept that particles can do things like be in two opposite states at once. With quantum computing, we’re using this weirdness to our advantage in two main ways. First, you can encode more information in a qubit than in a conventional bit. Two conventional bits, for instance, will have one of four possible values: 00, 01, 10, or 11. Each qubit, though, can be both a zero and a one at the same time, so two qubits can be all four possibilities at once. As you add more qubits, the amount of information you can store and process goes up incredibly fast. With a 300 qubit computer, you could do more calculations at once than there are atoms in the universe. Basically, a big enough quantum computer would be infinitely more powerful than the best supercomputer we could ever build the regular way, and it’s why physicists have been geeking out over this ever since they realized it was theoretically possible. The second main advantage of quantum computing is that you can use qubits to send information in a way that’s inherently secure. When you encrypt information, you jumble it up so that when you send it, anyone listening in won’t be able to decipher the message. But the person you’re sending it to, who you actually /want/ to read it, needs to be able to decode it, so you send them a key they can use to decrypt the message. Problem is, if someone’s eavesdropping on the key, they’ll be able to decode it too. There are lots of ways cryptographers try to get around this, but they all have some flaws, and in theory could be hacked eventually. Quantum computing, on the other hand, might be the perfect answer because of another weird rule of quantum mechanics: When you measure something like an electron’s spin, the act of taking the measurement actually /changes/ some of the electron’s properties. So if you use qubits to send your friend Bob a key, and your archnemesis Eve intercepts any of the particles before sending them along to Bob, you and Bob will be able to tell that someone messed with the qubits before he got them. In other words: no one can eavesdrop on your key without you knowing about it. This is next-order encryption, and we’d like to take advantage of it. But that means having more than one quantum computer, and hooking them up over long distances. Basically, we want to build a quantum internet. And that’s where this new research comes in. We already have a massive global network of fiber optic cables, so it’d be great to piggyback on our existing infrastructure as we build the internet of the future. And fiber optic cables are a pretty good choice, because you can use photons of light as qubits. But there are two big challenges. First, to use those fiber optic cables, you need to transmit photons with a certain wavelength. Second, qubits are super fragile. If anything interferes with the particles before you transfer your message, you’ve lost your data. So you need to keep your qubits stable. We’ve already discovered how to use certain materials to store quantum information for long enough to send it through a network, but they don’t work on the right wavelength for our fiber optic cables. And the materials that are compatible with those cables can store information for only a fraction of a second. That’s too short. To solve this problem, the Australian team wanted to find a way to lengthen that time. So they started experimenting with a crystal that had some erbium in it. Erbium is a rare earth metal, and a crystal with erbium ions in it can work on a wavelength that matches fiber optic cables, but it can only store quantum information for short bursts. To increase that timeframe, the group applied a super-strong 7 Tesla magnet. That’s the strength of the most powerful MRI machines. Magnets are helpful because they can freeze electrons in the crystal in place, which keeps them from interfering with and destroying the data. And … it worked! The magnet increased the crystal’s storage time to 1.3 seconds. Now, that might not seem very long, but it’s a 10,000-fold improvement over what scientists could do before — and it’s good enough for a quantum internet. Other experts have estimated that with quantum repeaters to boost the signals, you need storage times of just 1 second to send messages 1000 kilometers. So, where’s our quantum internet? Any kind of widespread network is still a ways off. For one thing, the Australian setup required very low temperatures to work: 1.4 Kelvin, or -272 Celsius. That’s seriously cold, and seriously expensive to maintain. And, of course, there’s that strong magnetic field. The researchers think their material will still work with a less powerful 3 Tesla magnet, but it’s not like that’s nothing. Think of a more typical MRI machine instead of the most advanced. Not exactly chump change. Even if we solve those problems, quantum networks might never be used for things like watching this video, or to execute run-of-the-mill Google searches. You know, like ‘quantum repeater’ or ‘erbium crystal’. They’ll be reserved for super-secret situations when you want your communication to be absolutely secure. So, maybe your banking, but probably more like high-level international intelligence. Basically, spy stuff. But no matter who ends up using it, the quantum internet will be a major upgrade for the world of cryptography. Thanks for watching this episode of SciShow News, and if you want to learn more about quantum computers, you can check out an earlier episode we did about another amazing quantum computing breakthrough.