Entanglement fidelity quantifies how well a quantum channel preserves the correlations between a transmitted system and an inaccessible reference system. We derive closed-form expressions for the entanglement fidelity associated with several standard quantum noise models, including the random Pauli-X, dephasing, depolarizing, Werner-Holevo, generalized Pauli (Weyl), and amplitude-damping channels. For each model, we express the entanglement fidelity in terms of a general input density operator $ρ$, using Schumacher's Kraus-operator approach, which provides a channel-agnostic recipe applicable to any completely positive trace-preserving (CPTP) map with a finite Kraus representation. We then specialize to a communication scenario in which the source emits a two-letter parametric alphabet, thereby making explicit the dependence of entanglement preservation on both channel and source parameters. The resulting expressions enable direct comparisons of channel performance and rankings for representative families of input states, including common qubit states.

翻译：纠缠保真度用于量化量子信道在多大程度上保持了传输系统与不可访问参考系统之间的关联性。我们推导了若干标准量子噪声模型所对应的纠缠保真度闭式表达式，包括随机泡利-X信道、退相位信道、退极化信道、Werner-Holevo信道、广义泡利（Weyl）信道以及振幅阻尼信道。针对每个模型，我们采用舒马赫的克劳斯算符方法，以一般输入密度算符$ρ$的形式表示纠缠保真度，该方法为具有有限克劳斯表示的任意完全正定保迹（CPTP）映射提供了与信道无关的通用计算框架。随后我们将研究聚焦于通信场景，其中信源发射双字母参数化字母表，从而明确揭示纠缠保持特性对信道参数与信源参数的双重依赖关系。所得表达式使得我们能够直接比较信道性能，并对包括常见量子比特态在内的典型输入态族进行信道排序。