Researchers at the University of California, Berkeley, have shown that heat can be carried across a vacuum using quantum mechanics. This challenges one of the fundamental understandings of heat transfer and opens up entirely new thermal management technques.
The paper in the journal Nature, shows that heat energy can leap across a few hundred nanometers of a complete vacuum via a quantum mechanical phenomenon called the Casimir interaction.
While this is significant on very short distances, it could have profound implications for the design of chips and other nanoscale electronic components where heat dissipation is key.
“Heat is usually conducted in a solid through the vibrations of atoms or molecules, or so-called phonons — but in a vacuum, there is no physical medium. So, for many years, textbooks told us that phonons cannot travel through a vacuum,” said Xiang Zhang, the professor of mechanical engineering at UC Berkeley who guided the study. “What we discovered, surprisingly, is that phonons can indeed be transferred across a vacuum by invisible quantum fluctuations.”
Zhang’s team placed two gold-coated silicon nitride membranes a few hundred nanometers apart inside a vacuum chamber, and found that the effectiveness of the transfer varied with the shape and thickness of the membranes. When they heated up one of the membranes, the other warmed up as well, even though there was nothing connecting the two membranes and negligible light energy passing between them
“We use nanomechanical systems to realize strong phonon coupling through vacuum fluctuations, and observe the exchange of thermal energy between individual phonon modes,” says the team in the paper. “The experimental observation agrees well with our theoretical calculations and is unambiguously distinguished from other effects such as near-field radiation and electrostatic interaction. Our discovery of phonon transport through quantum fluctuations represents a previously unknown mechanism of heat transfer in addition to the conventional conduction, convection and radiation.”
Theorists have long speculated that the Casimir interaction could help molecular vibrations travel through empty space, but proving it experimentally has been a major challenge.
“This discovery of a new mechanism of heat transfer opens up unprecedented opportunities for thermal management at the nanoscale, which is important for high-speed computation and data storage,” said Hao-Kun Li, a former Ph.D. student in Zhang’s group and co-first author of the study. “Now, we can engineer the quantum vacuum to extract heat in integrated circuits.”