Breaking boundaries: Researchers isolate quantum coherence in classical light systems

Understanding the boundary between classical and quantum physics has long been a central question in science. While thermal light fields have traditionally been viewed as classical, the team fragmented these fields into smaller multiphoton subsystems. Surprisingly, they uncovered quantum coherence—features such as particle interference previously thought unique to quantum systems—within a classical light source.

By using a sophisticated technique involving photon-number-resolving detection and orbital angular momentum (OAM) measurements, the researchers projected a classical pseudothermal light field into isolated multiphoton subsystems. They observed two contrasting behaviors:

       1.    Classical Coherence: Most subsystems behaved predictably, in line with traditional classical optics.

       2.    Quantum Coherence: A smaller subset exhibited quantum interference patterns similar to phenomena seen in entangled photon systems.

“This discovery shows that even a classical system hosts hidden quantum dynamics,” said Prof. Chenglong You, the study’s lead author. “We’ve unveiled novel mechanisms to isolate quantum systems, which could lead to more robust quantum technologies.”

The ability to extract quantum behaviors from classical systems offers new opportunities for developing advanced quantum technologies. From quantum imaging to quantum-enhanced sensors, this work provides a fundamental platform for mitigating decoherence and accessing quantum properties in open systems. The findings highlight universal quantum behaviors in many-body systems with broad applications, including condensed matter physics and quantum information science. Moving forward, this platform could be instrumental for engineering scalable quantum technologies at room temperature.

The study was a collaborative effort led by researchers from Louisiana State University and Universidad Nacional Autónoma de México. It was supported by funding from the U.S. Army Research Office, the Department of Energy, the National Science Foundation and DGAPA‑UNAM.