Scientists develop first chip containing two entangled quantum light sources

Recently, the Niels Bohr Institute at the University of Copenhagen, in collaboration with Ruhr University Bochum, has solved a problem that has been a headache for quantum researchers for years [1].

Researchers can now control two quantum light sources instead of one. Although seemingly trivial, this huge breakthrough allows researchers to create the phenomenon of "quantum mechanical entanglement", which in turn will open new doors for companies and others to use quantum technology commercially.

A chip consisting of two entangled quantum light sources

From 1 to 2: The first step in "quantizing" existing devices

In most cases, going from 1 to 2 is a small achievement; but in the world of quantum physics, doing so is crucial. For years, researchers around the world have been working to develop stable quantum light sources and to realize the phenomenon of quantum mechanical entanglement: a phenomenon with almost science-fictional properties, where two light sources can immediately interact with each other and may span large geographical distances. Not only that, but entanglement is the basis of quantum networks and is central to the development of efficient quantum computers.

This time, the latest results published by the Niels Bohr Institute team in the journal Science [2] show that they have succeeded in doing just that. According to Professor Peter Lodahl, one of the researchers of the results, this is a key step in the effort to take quantum technology to the next level and "quantumize" computers, encryption and the Internet.

"We can now control two quantum light sources and connect them to each other. That may not sound like much, but it's a major advance that builds on the work of the past 20 years. By doing so, we reveal the key to scaling up the technology, which is critical for the most groundbreaking quantum hardware applications."

Illustration of photon-mediated coupling between two quantum dots in a photonic crystal waveguide, where one quantum dot is optically pumped. Subsequently, the emission dynamics of the coupled quantum dot system exhibits superradiation and subradiation, which arise from constructive (bright lines) or destructive (dark lines) interference of the fields emitted into the photonic crystal waveguide and scattering from each quantum dot.

Optical quantum technology with performance stronger than supercomputers

Peter Lodahl's group is working on a quantum technology that uses particles of light called photons as microscopic transporters to move quantum information.

The project team, from left to right: Peter Lodahl, Anders Sørensen, Vasiliki Angelopoulou, Ying Wang, Alexey Tiranov, Cornelis van Diepen

Although Lodahl's group is a leader in this discipline of quantum physics, until now they have been able to control only one light source at a time. This is because light sources are extremely sensitive to external "noise", making them very difficult to replicate. In their new result, the group has succeeded in creating two identical quantum light sources, rather than just one.

"Entanglement means that by controlling one light source, it immediately affects the other. This makes it possible to create an entire network of entangled quantum light sources, all of which interact with each other, and you can make them operate with quantum bits in the same way as bits in a normal computer, only much more powerful." explained Alexey Tiranov, a postdoctoral fellow and lead author of the article.

This is because a quantum bit can be both a 1 and a 0, which results in processing power that is unattainable using today's computer technology. According to Professor Lodahl, just 100 photons from a quantum light source will contain more information than the world's largest supercomputers can process.

By using 20-30 entangled quantum light sources, it is possible to build a fault-tolerant quantum computer - the ultimate "holy grail" of quantum technology; today, large IT companies are investing billions of dollars to achieve this goal.

Deploying quantum physics on the applications side: computers, the Internet, cryptography

According to Lodahl, the biggest challenge is to go from controlling one quantum light source to two quantum light sources. Among other things, this has made it necessary for researchers to develop extremely quiet nanochips with precise control of each light source.

With the new research breakthroughs, the basic quantum physics research is in place. Now it's time for other actors to embrace the researchers' work and use it in their quest 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 device where we control 15-20 quantum light sources. So now that we have contributed to the understanding of fundamental quantum physics and taken the first steps along the way, further scaling up will largely be a new technical task." Professor Lodahl said.

Reference links：

[1]https://nbi.ku.dk/english/news/news23/danish-quantum-physicists-make-nanoscopic-advance-of-colossal-significance/

[2]https://www.science.org/doi/10.1126/science.ade9324