Members of the SNI network have developed a new theoretical approach to thermodynamics for quantum systems that interact with light. The researchers led by Prof. Dr. Patrick Potts (Department of Physics, University of Basel) take into account that that the light emitted by such a system can contain useful energy, not just waste heat. 

The quantum systems under investigation interact with light confined between mirrors and form an optical “cavity”. These systems play a central role in many modern technologies, from lasers to emerging platforms for quantum communication and computation. However, understanding how these systems use and convert energy remains a challenge. 

Unlike in the macro world
In the macroscopic world that is familiar to us, we can clearly distinguish between work (useful energy) and heat (waste energy) in an engine, for example. In the quantum world, the standard approach to thermodynamics treats all light leaving a cavity as heat and thus as waste energy, even when this light is actually useful, as in a laser’s output. 

The new approach recently published in Physical Review Letters by the researchers from Basel distinguishes between the useful energy emitted, stored in the average amplitude of the light, and the part that is truly lost, stored in random fluctuations. 

“This refined analysis allows us to meaningfully discuss energy conversion and efficiency in optical cavities and networks thereof,” notes Max Schrauwen from the RWTH Aachen. “Such networks could be the foundation of a quantum internet and our framework is an essential step towards understanding the thermodynamics of these future quantum technologies”, adds Aaron Daniel from the Potts team.

Original publication
Max Schrauwen, Aaron Daniel, Marcelo Janovitch and Patrick P. Potts
Thermodynamic framework for coherently driven systems
Physical Review Letters (2025), doi: 10.1103/zdbv-rksc

Further information
Forschungsgruppe Prof. Dr. Patrick Potts
https://qtd.physik.unibas.ch/en/