In a major milestone for quantum research, scientists from the University of Copenhagen, in collaboration with Ruhr University Bochum, have achieved what was previously thought impossible—simultaneous control over two quantum light sources. Until now, researchers had only been able to manage one, making this a pivotal step forward for the future of quantum technology.
To those outside the field, the feat may seem modest. But within the realm of quantum, it's a transformational leap. The breakthrough enables entanglement between two light sources, paving the way for future computing, encryption, and network applications powered by quantum systems.
Mastering the interaction of multiple quantum light sources is essential for building scalable quantum networks. Entanglement—the phenomenon where two particles remain interconnected regardless of distance—is central to quantumphysics. Without it, efforts to create ultra-fast quantumcomputers and advanced cybersecurity solutions would stall.
The findings, recently published in Science, mark a turning point. Researchers from the Niels Bohr Institute believe this could accelerate the commercialization of quantum technologies.
Peter Lodahl, who led the initiative, described it as a major step forward. "We can now control two quantum light sources and connect them. It might not sound like much, but it’s a major advancement and builds upon the past 20 years of work," he shared.
Lodahl, who has been investigating the potential of quantum light since 2001, added: "By doing so, we’ve revealed the key to scaling up the technology, which is crucial for the most groundbreaking of quantum hardware applications." This progress propels the global race to develop quantum-based computers, security, and even a new form of the internet.
The innovation stems from a custom-designed nanochip, only slightly wider than a human hair. Developed over several years, this chip has become the foundation for this scientific leap.
Lodahl's team specializes in photon-based quantum communication, where particles of light transport information. Until this breakthrough, the challenge was that these light sources were too sensitive to external disturbances, limiting control to just one at a time. Now, they've succeeded in developing two identical, noise-resistant quantum light sources.
"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," explained lead author and postdoctoral researcher Alexey Tiranov.
A quantumbit, or qubit, can exist as both a 1 and 0 simultaneously—enabling processing speeds that dwarf traditional systems. As Lodahl notes, 100 photons from a single quantum light source contain more information
than the world's largest supercomputer can process.
With 20-30 entangled light sources, scientists could construct a universal, error-corrected quantum computer—the ultimate prize in this field. Leading technology companies are already investing billions into this endeavor.
The biggest obstacle? Scaling from one to two light sources. This required crafting ultra-quiet nanochips and achieving precise control over both light sources. With that now achieved, the foundational research is in place. The next step: transitioning from lab success to real-world quantum systems.
"It is too expensive for a university to build a setup 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," said Lodahl.
The research was conducted at the Danish National Research Foundation's Center of Excellence for Hybrid Quantum Networks (Hy-Q), a joint effort between the University of Copenhagen’s Niels Bohr Institute and Ruhr University Bochum in Germany.
