Quantum entanglement breakthrough sees Danish physicists achieve world first

For the first time, physicists have achieved quantum mechanical entanglement of two stable light sources.

Called “spooky action at a distance” by Einstein, quantum entanglement is a seemingly magical phenomenon. Entangled particles, for example light particles called “photons”, share a physical state. Changes to the physical state of one particle in an entangled pair instantaneously causes the same change to occur in its partner – no matter how far apart they are separated.

While quantum mechanical theory is clear on the existence of this effect in the universe, creating entangled pairs of particles is no trivial feat.

But mastery of quantum entanglement could revolutionise technology through the development of quantum networks, unhackable encryption and error-corrected super-powerful quantum computers.

“We can now control two quantum light sources and connect them to each other,” says one of the researchers behind the recent breakthrough, Professor Peter Lodahl from the Niels Bohr Institute at the University of Copenhagen, Denmark.

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“It might not sound like much, but it’s a major advancement and builds upon the past 20 years of work. By doing so, we’ve revealed the key to scaling up the technology, which is crucial for the most ground-breaking of quantum hardware applications.”

Lodahl’s team performed their experiment on a nanochip they developed which is about as large as the diameter of a human hair.

Until now, the researchers have only been able to control one light source at a time. This is because light sources are extremely sensitive to outside “noise”.

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“Entanglement means that by controlling one light source, you immediately affect the other,” explains postdoc Alexey Tiranov, lead author of a paper published on the research in journal Science. “This makes it possible to create a whole network of entangled quantum light sources, all of which interact with one another, and which you can get to perform quantum bit operations in the same way as bits in a regular computer, only much more powerfully.”

Lodahl says that just 100 photons emitted from a single quantum light source would contain more information than can be processed by the world’s largest supercomputer.

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