Amid growing hopes for quantum technology, scientists have demonstrated the first proven quantum advantage in a photonic system.
A new study shows how entangled light slashes the number of measurements needed to learn the noise of a quantum system.
Researchers at the Technical University of Denmark (DTU) led the work with partners from the US, Canada, and South Korea.
They used an optical setup that showed entangled light could identify the behaviour of a noisy quantum system far faster than classical approaches.
“This is the first proven quantum advantage for a photonic system,” said corresponding author Ulrik Lund Andersen, a professor at DTU Physics. “Knowing that such an advantage is possible with a straightforward optical setup should help others look for areas where this approach would pay off, such as sensing and machine learning.”
At the heart of the study lies a long-standing challenge. When scientists want to understand a physical device, they must repeat measurements to determine its “noise fingerprint.” For quantum devices, the problem intensifies.
Quantum noise is built into measurements, and the number of required trials grows exponentially as systems get larger.
“We built a process we could control and asked a simple question: Does entanglement reduce the number of measurements you need to learn such a system? And the answer is yes, by a lot,” said Andersen.
He added that the team learned the behaviour of their system in 15 minutes. A comparable classical method would take around 20 million years.
Simple but powerful setup
The experiment took place in the basement labs at DTU Physics. The team used standard optical parts running at telecom wavelengths.
Even with ordinary losses in the setup, the system worked. That, they noted, showed the advantage came from the measurement method, not from ideal equipment.
The setup relied on an optical channel where multiple light pulses shared the same noise pattern. Two beams of light were squeezed until they became entangled. One beam probed the system while the other served as reference.
A joint measurement compared them in a single shot, cancelling much of the noise and extracting more information per trial than classical approaches.
That work suggested entangled light would deliver the needed leap, which the current experiment confirmed.
A step for quantum technology
The researchers stress they have not yet targeted a specific real-world system. Still, the breakthrough confirms a long-sought goal for quantum physics.
“Even though a lot of people are talking about quantum technology and how they outperform classical computers, the fact remains that today, they don’t,” said co-author Jonas Schou Neergaard-Nielsen, associate professor at DTU Physics. “So, what satisfies us is primarily that we have finally found a quantum mechanical system that does something no classical system will ever be able to do.”
The study is published in the journal Science.