Physicists achieve quantum mechanical entanglement breakthrough

Researchers at the University of Copenhagen, in collaboration with Ruhr University Bochum, have controlled two quantum light sources rather than one. This allows researchers to create a phenomenon known as quantum mechanical entanglement, which in turn opens new doors for companies and others to use the technology commercially.

For years, researchers have strived to develop stable quantum light sources and achieve quantum mechanical entanglement — a phenomenon where two light sources can affect each other instantly and potentially across large geographic distances. Entanglement is the basis of quantum networks and central to the development of an efficient quantum computer.

Researchers from the Niels Bohr Institute published a result in the journal Science, in which they outlined how they achieved quantum mechanical entanglement. Professor Peter Lodahl, one of the researchers behind the result, said it is a crucial step in the effort to take the development of quantum technology to the next level and to “quantize” society’s computers, encryption and the internet.

“We can now control two quantum light sources and connect them to each other. 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 said.

The development concerned a so-called nanochip — which is not much larger than the diameter of a human hair — that the researchers also developed in recent years. Lodahl’s group is working with a type of quantum technology that uses light particles, called photons, as micro transporters to move quantum information about. Lodahl’s group has only been able to control one light source at a time until now, because light sources are sensitive to outside ‘noise’, making them difficult to copy. In their new result, the research group succeeded in creating two identical quantum light sources rather than one.

Alexey Tiranov, the article’s lead author, said entanglement means that by controlling one light source, you immediately affect the other. “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,” Tiranov said.

This is because a quantum bit can be both a 1 and a 0 at the same time, which results in processing power that is unattainable using today’s computer technology. According to Lodahl, just 100 photons emitted from a single quantum light source will contain more information than the world’s largest supercomputer can process. By using 20–30 entangled quantum light sources, there is the potential to build a universal error-corrected quantum computer. According to Lodahl, the biggest challenge has been to go from controlling one to two quantum light sources. Among other things, this has made it necessary for researchers to develop quiet nanochips and have precise control over each light source.

With this development, the fundamental quantum physics research is now in place, for other researchers to take the research findings and use them in their quests to deploy quantum physics in a range of technologies including computers, the internet and encryption. “It is too expensive for a university to build a set-up where we control 15–20 quantum light sources. So, now that we have contributed to understanding the fundamental quantum physics and taken the first step along the way, scaling up further is very much a technological task,” Lodahl said.

Image caption: Illustration of a chip comprising two entangled quantum light sources. Image credit: Niels Bohr Institute