Quantum entanglement can be used to encrypt messages – making data more secure

The way we currently send secure information over the internet – like credit card details – is under threat from quantum computing. Our current methods of encrypting data are very difficult to crack with current computers, but the next generation of quantum computers would be able to do it.

But two new studies suggest that, just as quantum physics causes problems for security, it might also be able to solve them.

The two papers, both published in Nature, demonstrate together a way to encrypt messages using quantum entanglement.

At the moment, secure information is sent publicly over the internet, the same as any other information. It’s just as easy to intercept credit card details and passwords as it is to intercept web searches.

Encryption is what keeps your credit card safe: the information is translated into a secret code, only decodable if you have the right key. Modern encryption depends on extremely complicated maths problems, solvable only with collections of algorithms that behave as keys. (For more detail on how encryption works, read our explainer.)

Diagram explaining quantum encryption using a photo of j. S. Bell, which is encrypted and turned into an illegible box of black and white snow.
Device-independent quantum key distribution, or DIQKD. A message is encrypted using a key made from quantum entanglement. Then, even if it’s sent over a public network, it can’t be read until it’s decrypted with a matching key. Credit: David Nadlinger/ University of Oxford, original photo of J. S. Bell: CERN

Eventually, we will develop powerful enough quantum computers that will be able to find these keys – rendering all that coded data public.

These two studies have shown that quantum entanglement can overcome this problem, by using quantum particles as keys.

“Two people who wish to create a secret key prepare, send and measure photons,” explains Krister Shalm, a researcher in the Department of Physics at the University of Colorado at Boulder, US, in a Nature News and Views article accompanying the two papers.

“The information encoded in the photon cannot be perfectly copied — any measurement of the system will disturb it.

“A hacker who is trying to intercept the information encoded in a photon will have to measure it in some way, and will therefore introduce anomalies into the system that the sender and receiver can detect.”

While this idea has been theorised for decades (in fact, since 1991), these two experiments are the first to show it works in the real world.

Black box connected to two clear boxes via wires, the two clear boxes each contain keys being made from tiny particles and glowing blue orbs
An artist’s rendition of device-independent quantum key distribution. Credit: Scixel/Enrique Sahagú

One team of Swiss, UK, and French researchers were able to encrypt, send, and decrypt a message using this quantum entanglement method. The sender and the receiver were only a couple of metres apart, and the whole process took eight hours, so it’s not yet particularly practical. But it’s a successful proof of concept.

In their paper, the researchers write that “the present apparatus could potentially be adapted to span building-scale local-area networks”. They also state that it’s theoretically possible to extend it over several kilometres.

More on encryption with quantum physics: ‘Beyond quantum’ link secures encryption, universal theory

A second team of German and Singaporean researchers have demonstrated that they could measure particles for encryption at a distance of 400 metres. This slowed the process down so much that it wasn’t feasible to send a message – but it does again provide evidence that it works.

“[Our results] indicate that state-of-the-art quantum links are capable of generating secret keys,” write the researchers in their paper.

They write that their findings are “a major step towards the goal of ultimate secure communication based solely on the laws of physics”.

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