New record in quantum entanglement gets us one step closer to quantum internet

Dan Broadbent

In a study published today, scientists report they entangled two quantum memories over "dozens of kilometers."

In a study published today in the journal Nature, scientists at the University of Science and Technology of China reported they successfully entangled two quantum memories over "dozens of kilometers."

Referred to by Einstein as "spooky action at a distance", quantum entanglement happens when a pair of particles like photons interact with one another.

As LiveScience explains:

The rules of quantum physics state that an unobserved photon exists in all possible states simultaneously but, when observed or measured, exhibits only one state. Spin is depicted here as an axis of rotation, but actual particles do not rotate. Entanglement occurs when a pair of particles, such as photons, interact physically. A laser beam fired through a certain type of crystal can cause individual photons to be split into pairs of entangled photons. The photons can be separated by a large distance, hundreds of miles or even more.

Once separated, when one of the particles is observed, it will instantly influence the measurement of the other particle, regardless of the distance they are separated. If you're familiar with Schrödinger's Cat, it's kind of like that.

Get it? Good.

Of course, information is not being exchanged between these two particles, because that would mean that information would be traveling faster than the speed of light. However, the usefulness of this comes from being able to create ultra-secure encryption. To hack the encryption, you'd have to hack the laws of physics itself, as New Scientist explains:

Their quantum memories were each made of about 100 million extremely cold rubidium atoms in a vacuum chamber. The quantum state of each system of atoms was entangled with the state of a single photon, and the researchers sent those photons through the fibre-optic cables.

When a particular observation called a Bell measurement was performed on the two photons simultaneously, the quantum memories with which the photons were paired before the measurement became entangled to one another.

While the team was able to entangle two quantum memories over 22 kilometers using an underground fiber optic cable, they were also able to entangle them over 50 kilometers on a cable that was coiled.

This gets us one step closer to having an ultra-secure encryption method using quantum internet.

MIT Technology Review explains how the encryption would work:

One technique is to encrypt a pair of digital keys, a technology known as quantum key distribution (QKD). If two people both have these keys, they can talk without fear of being snooped on, because an eavesdropper would change the state of the keys and be found out.

But QKD relies on measuring the state of the quantum-encrypted keys, and since that measurement can be affected by conditions in the sending and receiving devices, you need to know their exact physical conditions. That can be impractical, especially because even tiny physical fluctuations can throw off the measurements.

They went on to explain that quantum keys aren't as useful for a quantum internet as entanglement would be, using entangled nodes in the network. This is because the connection would completely bypass the actual devices. And observing the state of the particles would then change their state, preventing the encrypted connection from being hacked.

Of course, the real-world implementation of this is quite a way's off. It requires ideal conditions to be successful, which isn't practical to scale-up. Progress is usually incremental though, and the researchers believe they can use the method they created in the near future to create quantum networks over long distances, outside of a laboratory setting.

Cover image via iStock

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