The time evolution properties of the quantum fidelity in a system of multi-mode coherent light field resonantly interacting with a two-level atom via any Nj-degenerate NΣ-photon transition process are studied by the fully quantum theory and numerical calculations. The analytical expressions of the quantum fidelity of field and atom, and the numerical calculation results for three-mode field interacting with the atom are obtained. Our attention focuses on the discussion of the influences of the initial average photon number, the atomic distribution angle, the phase angle of the atom dipole, the field excitation angle, and the atomic degeneracy on the evolution of the quantum fidelity. The results obtained from the numerical calculation indicate that the above factors lead to the quantum fidelity changing with oscillation behavior. The quantum fidelity of field and atom will drastically decrease as the initial light increases, which is correlated sensitively with the fidelity. The speed change of quantum fidelity is strongly dependent on the atomic degeneracy and the intensity coupling between atoms and fields. The value and frequency of the quantum fidelity change lightly with the atomic distribution angle and the angle of light field excitation as well. The phase angles of the atom dipole almost have no influences on the quantum fidelity of field and atom. According to these properties of the quantum fidelity, we can control the speed and value of quantum fidelity in the system by these constraint conditions.%利用全量子理论和数值计算方法研究了多模相干态光场与单个二能级原子通过任意Nj 度简并NΣ光子共振相互作用系统中量子保真度的时间演化特性，给出了三模场与原子相互作用过程中光场和原子保真度的数值计算结果，详细讨论了初始平均光子数、原子分布角、原子偶极相位角、光场激发角以及原子简并度等对量子保真度的影响。数值计算结果表明：以上诸多因素对量子保真度影响的结果均导致其发生振荡性变化。光场和原子保真度随着初始光场增强而急剧减小，说明初始光强敏感地影响着保真度的大小；量子保真度的变化快慢程度强烈地依赖于原子简并度及场-原子的耦合系数；原子分布角、光场激发角不同程度地对量子保真度的大小和频率有所影响；而原子偶极相位角的变化对场和原子的量子保真度几乎没有影响。根据这些特性，通过某些条件的约束可以适当控制保真度变化的快慢及其大小。
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