Quantum advantage—where quantum technologies outperform their classical counterparts to solve specific tasks—has long been the goal of quantum information science researchers.
Now, University of Chicago Pritzker School of Molecular Engineering (UChicago PME) researchers are part of an international, multi-institution collaboration that has shown a significant speed-up in using quantum learning techniques to characterize physical systems.
By harnessing the unique quantum phenomenon of entanglement, the research team directly probed the properties of a quantum system in a way not possible with classical techniques.
In fact, the team showed that while a classical, entanglement-free approach to these measurements would take 20 million years, their quantum, entanglement-enhanced approach took less than 15 minutes.
“Through both rigorous theory and experiments, we tie the origin of this quantum advantage to quantum entanglement,” said Prof. Liang Jiang, who led UChicago PME’s team in the collaboration. “Ultimately, we could take these quantum signals and process them with a quantum processor, allowing us to have more applications with quantum advantage.”
"Quantum science has reached an extraordinary stage, where theorists can dream up a scheme for exploiting quantum entanglement to perform measurements that would otherwise be impossible, and a heroic team of experimentalists can swiftly turn that dream into reality,” said Prof. John Preskill of the California Institute of Technology, a co-author on the paper.
Other institutions involved include Technical University of Denmark, Perimeter Institute for Theoretical Physics, University of Waterloo, Massachusetts Institute of Technology, and Korea Advanced Institute of Science and Technology (KAIST).
Quantum advantage with entanglement
When scientists and engineers probe a physical system—like the Earth’s atmosphere, for example—they generally take measurements of certain variables (like water vapor) and use software to apply statistical methods to estimate the variables’ distribution. That graph can then be used to infer information about the properties of the system (the effects of climate change.)
But quantum systems are much more difficult to measure, since they adhere to Heisenberg’s uncertainty principle. That states that we cannot accurately measure both the position and the momentum of a quantum particle. This might lead to the impression that scientists cannot monitor changes in position and momentum simultaneously.
But scientists and engineers have found a way around this conundrum by using what are called Einstein-Podolsky-Rosen (EPR) entangled states. Entanglement, a unique feature of the quantum realm, allows particles to share a quantum state. The research team prepared an EPR entangled state of a probe mode and a memory mode on a photonic continuous variable platform, an architecture that has been used for quantum sensing and computing.
This special entangled state allowed researchers to measure the sum of an oscillator’s position and the difference of its momentum simultaneously. “We used entanglement to get around the uncertainty principle and simultaneously monitor changes of position and movement,” Jiang said.
The team prepared up to a hundred of these entangled modes, which went through random changes of position and momentum draw from some unknown higher dimensional distribution. The possible random changes of position and momentum increase exponentially with the number of modes. While previous measurements of such quantum systems could only provide limited information of the unknown distributions of measurements, this team had direct information about measurement distribution.
In doing so, they learned learn the amplitude and phase distributions of the oscillators with 1011 times fewer samples than required by an approach without entanglement.
Theoretical proof seals the advantage
The researchers have spent several years developing a rigorous mathematical proof, as well as designing experiment to unambiguously demonstrate the quantum advantage.
“And with those two parts together, between theory and experiment, we can unambiguously show that there is a barrier, that it's the quantum entanglement that enables this advantage,” Jiang said. “Which is a very clear message that where the borderline between quantum and the classical is in this particular setting.”
“This is an exciting theoretical proposal using the quantum property of light to probe the fascinating physical world,” said Zhenghao Liu, a postdoctoral fellow at the Technical University of Denmark and co-author of the paper. “And we are happy that we managed to demonstrate and validate it experimentally.”
Potential applications include quantum sensors, which could be used in environmental monitoring or medical imaging. “It’s a very interesting quantum tool, and we look forward to talking with other research team to discover new use cases,” Jiang said.
Other authors on the paper include Senrui Chen, a former UChicago student who is now a postdoctoral researcher at Caltech, Changhun Oh, a former postdoctoral researcher at UChicago who is now at KAIST, Romain Brunel, Emil E. B. Østergaard, Oscar Cordero, Yat Wong, Jens A. H. Nielsen, Axel B. Bregnsbo, Sisi Zhou, Hsin-Yuan Huang, Jonas S. Neergaard-Nielsen, and Ulrik L. Andersen.
Citation: “Quantum learning advantage on a scalable photonic platform,” Liu et al. Science. Sept. 25, 2025. DOI: 10.1126/science.adv2560
Funding: Army Research Office, Air Force Office of Scientific Research, Department of Defense, National Science Foundation, NTT Research, and the Packard Foundation