While apps like Signal make it possible to exchange encrypted communications, no system is fully secure. But, owing to quantum mechanics, the esoteric area of science that regulates the cosmos at the lowest scales, encryption may become far more difficult to crack in the future.
You’re almost probably viewing this on an electrical gadget that relies on silicon-based transistors to work at its most basic level. Each of those bits carries a single number in the non-quantum realm, which physicists refer to as the “classical” universe.
Quantum devices have their quantum bits, or “qubits” (pronounced “Q-bits”), that follow quantum mechanics’ principles. This enables qubits to behave in strange and wonderful ways. For example, a qubit may hold both zero and one at the same time.
Photons, for example, which scientists can send via the fiber-optic cables that support the traditional internet, may be sent through a quantum network.
These networks, which are still in the experimental stage, are used to connect quantum devices. “Now that quantum computers are starting to be created, people are starting to think more seriously about networking them,” says Christoph Simon, a researcher at the University of Calgary who specializes in quantum optics.
Building a quantum computer is difficult enough, but making quantum computers larger is considerably more difficult. According to Oliver Slattery, a physicist at the National Institute of Standards and Technology, “one method to scale up the processing power would be to entangle many networked quantum computers to create a single ‘super’ quantum computer.”
However, the initial (and most well-known) application of quantum networks is to construct connections that are considerably more incomprehensible in principle than anything on the extremely flawed classical internet.
The quantum entanglement concept is used to create these ultra-secure links. To put it another way, you may make particles that are “entangled.” Observing the state of one of them will impact the state of its entangled partner, regardless of how far away that other particle is.
It’s possible to encrypt data using this method. Let’s say you want to send a message to your spy pal in the next city over. One of a pair of entangled photons would be given to each of you. Measuring the states of those photons would provide you and your colleague with a unique key, which you could use to encrypt a message and your buddy to decode it.
If someone tried to tap in for the key, the photons would be affected, and you’d know. “You can’t eavesdrop and conduct measurements on the channel without people noticing,” says Nathalie de Leon, a Princeton University professor of electrical and computer engineering. “You also can’t merely intercept and duplicate the data.”
Another quantum oddity known as the “no-cloning principle” prevents you from copying a qubit. That same concept, however, is a quantum network’s fatal weakness. When a qubit is sent down a line, it can only travel so far before it fades. You may just forward such information on the traditional internet. But in the quantum realm, you can’t replicate a qubit, therefore it won’t work.
As a result, quantum networks can only send qubits a few kilometers distant at the moment. That implies you can’t send qubits over fiber at a scale greater than a city right now.
“To be able to do anything at larger distances,” adds de Leon, “fundamentally new technologies are required.” There are shortcuts, but they aren’t always safe. They’re like having your message relayed through intermediaries, and middlemen aren’t necessarily trustworthy.
It’s also feasible to send a qubit through what’s known as “free space”—literally the open air—rather than fiber. It’s as though a light is being flashed from one peak to the next. It’s impossible to perceive the other side without personally seeing it, which is impracticable in most instances. It’s also susceptible to atmospheric influence.
However, in the vacuum of space, it works. In 2017, the Chinese satellite QUESS was able to “teleport” a qubit from orbit to the ground. Although the technology is sluggish and inefficient, the scientists behind QUESS (and the Chinese government) believe that it may one day serve as the foundation for a quantum satellite network.
As remarkable as the achievement is, de Leon points out that it builds on previous work. “It was a significant display… “I believe we as a community learn a lot,” she says. “However, what they did could have been written down ten, fifteen years ago.”
Still, some scientists are focusing their efforts there, constructing ground stations to collect qubits from space. QUESS won’t be alone for long: Several Canadian experts, notably Christoph Simon, will be in charge of another spacecraft, QEYSSat.
“We’re trying to figure out what’s feasible and reasonable,” Simon adds. “To be honest, we’re already planning the next [satellite].”
Is it possible that all of these connections may ultimately coalesce into a “quantum internet”? After all, the traditional internet started as a nascent network of links spun between labs and colleges.
There’s a long way to go before that happens, and there are plenty of technological hurdles to overcome along the way. Quantum computers, for example, must operate at extremely low temperatures, just above absolute zero. However, most fiber-optic cables do not operate at such low temperatures. As a result, any connection between the two must overcome the temperature differential.
The main problem, however, is that no one can agree on what to use to create a quantum network. Today’s quantum networks rely on relatively simple hardware. Scientists are working on more sophisticated nodes that can utilize quantum trickery, circumvent the no-cloning principle, and create longer quantum networks in the future.
De Leon says, “We haven’t… found the thing that’s like the silicon-based transistor.”
Qubits can be read by trapping them in rubidium vapor, according to some researchers. Others seek to make a magnetic cage to accomplish something similar. De Leon’s company intends to employ diamonds, which are (literally) dazzling. The “nitrogen-vacancy center,” a form of defect found in diamonds, can function as a quantum memory.
“The fundamental unit is still up for grabs,” de Leon argues.
Quantum networks will, for the most part, remain lab-bound until basic challenges like these are resolved. Quantum networks, as fascinating as they are, are unlikely to entirely replace the Internet anytime soon.
According to Slattery, “classical networks will almost certainly need to run alongside quantum networks to make them useable in a practical sense.”