该研究团队证明了负光学温度的等熵膨胀-压缩和焦耳膨胀，这是通过在热力学微正则光子系统中纯非线性光子-光子相互作用实现的。他们的光子方法为探索新型全光学热机提供了一个平台，并有望在光学以外的其他玻色系统（如冷原子和光力学）中产生影响。
据悉，根据统计力学的要求，如果系统的内能没有上限，那么系统的温度必须为正数。然而，如果这个条件不成立，高阶能态在热力学上倾向于成为主要的能态，这就导致了负温度的产生。虽然在自旋和玻色-哈伯德设置以及量子流体中曾报道过负温度现象，但在这个区域内观察热力学过程目前仍然难以实现。
附：英文原文
Title: Observation of photon-photon thermodynamic processes under negative optical temperature conditions
Author: A. L. Marques Muniz, F. O. Wu, P. S. Jung, M. Khajavikhan, D. N. Christodoulides, U. Peschel
Issue&Volume: 2023-03-10
Abstract: Statistical mechanics demands that the temperature of a system is positive provided that its internal energy has no upper bound. Yet if this condition is not met, it is possible to attain negative temperatures for which higher-order energy states are thermodynamically favored. Although negative temperatures have been reported in spin and Bose-Hubbard settings as well as in quantum fluids, the observation of thermodynamic processes in this regime has thus far remained elusive. Here, we demonstrate isentropic expansion-compression and Joule expansion for negative optical temperatures, enabled by purely nonlinear photon-photon interactions in a thermodynamic microcanonical photonic system. Our photonic approach provides a platform for exploring new all-optical thermal engines and could have ramifications in other bosonic systems beyond optics, such as cold atoms and optomechanics.
DOI: ade6523
Source: https://www.science.org/doi/10.1126/science.ade6523