與量子化電磁場作用的帶電粒子的非平衡有效作用量，可用閉時路徑公式，在一般協變規範下，
藉由積分掉場變數而求得。由此可得帶電粒子的化約密度矩陣，並藉著在電磁量子化擾亂之影響下的干涉實驗，可根據去同調函數W 的觀點探討帶電粒子的 量子去同調現象。在本論文中，亦討論到去同調函數的規範不變性。

The nonequilibrium effective action for a charged particle interacting with the quantized electromagnetic fields is derived within the context of the closed-time-path formalism by integrating out field variables
in general covariant gauge. The reduced density matrix of the charged particle is then obtained, thus enabling us to explore quantum decoherence phenomena of the charged particle in terms of the decoherence
functional W by an interference experiment under the influence of electromagnetic quantum fluctuations.The issue of gauge invariance of the decoherence functional is discussed.PACs numbers: 03.65.Yz, 05.40.a, 42.50.Lc