UCLA engineers observe quantum heat waves at room temperature

Researchers at the UCLA Samueli School of Engineering have demonstrated for the first time that phonons — atomic vibrations that carry heat — can travel in focused, ray-like paths at room temperature, a phenomenon previously observed only near absolute zero. The findings, published July 22 in Nature Physics, could reshape how engineers manage heat in electronics, AI hardware, and quantum devices.newsroom.ucla+1

Phonon Focusing in Boron Arsenide

The study, led by Yongjie Hu, a professor of mechanical and aerospace engineering at UCLA Samueli, showed that in boron arsenide — a crystalline semiconductor with high thermal conductivity — heat does not spread uniformly in all directions as it does in conventional materials. Instead, it moves along guided pathways dictated by the material's crystal structure, much like how optical fibers channel light.samueli.ucla+1

To capture the effect, the team developed a nanoscale temperature-mapping technique. In ordinary materials, they observed circular heat-spreading patterns consistent with diffusive conduction. In boron arsenide, however, they recorded ray-like temperature patterns that changed predictably with crystal orientation, producing distinct sixfold, eightfold, and fourfold focusing patterns depending on the crystal plane examined.newsroom.ucla

The quantum phonon behavior persists over distances of one micrometer and potentially up to tens of micrometers — distances relevant to modern electronic, photonic, and quantum devices.samueli.ucla+1

Implications for Future Technology

"This is a fundamental observation that enables us to think about thermal management in a new way," Hu said. "By enabling heat to be guided, focused and redistributed with nanoscale precision at room temperature, the discovery establishes a foundation for quantum thermal engineering."newsroom.ucla

Previous observations of phonon focusing required cryogenic temperatures — typically only a few degrees above absolute zero — where phonons can travel long distances without scattering. At room temperature, phonons had been thought to scatter too rapidly for such coherent behavior to emerge. Boron arsenide's unusually weak phonon scattering enables wave-like transport to persist under ambient conditions.nature+1

The discovery builds on Hu's earlier work pioneering the experimental characterization of boron arsenide in 2018. Controlling heat at the atomic level could help address thermal bottlenecks limiting the performance of AI chips, microelectronic devices, and aerospace systems, while also opening pathways to fine-tune how phonons interact with electrons in quantum information and sensing technologies.newsroom.ucla