Making Thermodynamics Work at Quantum Scale

Physicists at the University of Basel have extended the laws of thermodynamics into the quantum realm, resolving a long-standing gap between classical physics and quantum behavior. Thermodynamics traditionally distinguishes “work” (useful energy) from “heat” (random energy), but in tiny quantum systems everything blurs together. The researchers developed a new formalism for laser-driven quantum systems that clearly defines work vs. heat on the quantum level. They showed that when a laser beam passes through a cavity with atoms, the coherent part of the light (ordered photons) can be treated as work capable of charging a “quantum battery,” while the incoherent, scattered light is treated as heat. Using this definition, a small quantum system obeyed both the First and Second Laws of thermodynamics – energy was conserved and entropy (disorder) never decreased. This approach, published in Physical Review Letters, essentially “fixes” thermodynamics for quantum machines, letting scientists calculate energy efficiency and loss even for single photons. “In the future, we can use our formalism to consider more subtle problems in quantum thermodynamics,” said co-author Aaron Daniel, noting it could inform emerging quantum technologies like quantum networks. By bridging microscopic quantum effects with macroscopic laws, the work could help design quantum engines, refrigerators, or batteries that operate near the limits of physics. It also sheds light on how classical thermodynamic behavior emerges from quantum systems, a fundamental question in physics