Li Changhao, Li Jianfeng, Yang Yuliang
The State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai 200433, China.
Entropy (Basel). 2022 Nov 4;24(11):1609. doi: 10.3390/e24111609.
This work is devoted to deriving the entropy of a single photon in a beam of light from first principles. Based on the quantum processes of light-matter interaction, we find that, if the light is not in equilibrium, there are two different ways, depending on whether the photon is being added or being removed from the light, of defining the single-photon entropy of this light. However, when the light is in equilibrium at temperature , the two definitions are equivalent and the photon entropy of this light is hν/T. From first principles, we also re-derive the Jüttner velocity distribution showing that, even without interatomic collisions, two-level atoms will relax to the state satisfying the Maxwell-Jüttner velocity distribution when they are moving in blackbody radiation fields.
这项工作致力于从第一原理推导光束中单个光子的熵。基于光与物质相互作用的量子过程，我们发现，如果光处于非平衡态，根据光子是被添加到光中还是从光中被移除，有两种不同的方式来定义这种光的单光子熵。然而，当光在温度(T)下处于平衡态时，这两种定义是等效的，并且这种光的光子熵为(h\nu/T)。从第一原理出发，我们还重新推导了尤特纳速度分布，表明即使没有原子间碰撞，二能级原子在黑体辐射场中运动时也会弛豫到满足麦克斯韦 - 尤特纳速度分布的状态。
