We present an alternative method for describing the evolution of a mode of the quantized electromagnetic field in contact with a finite temperature thermal bath. We use the expansion of the field density operator in terms of coherent states and the related Glauber-Sudarshan $P$-function in phase space. The method allows us to obtain analytical expressions of the system's time-evolved $P$-function without needing to solve the corresponding master equation.

中文翻译：

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耦合到热浴的量子场的时间演化：一种相空间方法

我们提出了一种替代方法来描述与有限温度热浴接触的量化电磁场模式的演变。我们在相空间中使用相干态和相关的 Glauber-Sudarshan $P$ 函数的场密度算子的扩展。该方法使我们无需求解相应的主方程即可获得系统随时间演化的 $P$ 函数的解析表达式。