Losses in quantum communication lines severely affect the rates of reliable information transmission and are usually considered to be state-independent. However, the loss probability does depend on the system state in general, with the polarization dependent losses being a prominent example. Here we analyze biased trace decreasing quantum operations that assign different loss probabilities to states and introduce the concept of a generalized erasure channel. We find lower and upper bounds for the classical and quantum capacities of the generalized erasure channel as well as characterize its degradability and antidegradability. We reveal superadditivity of coherent information in the case of the polarization dependent losses, with the difference between the two-letter quantum capacity and the single-letter quantum capacity exceeding 7.197 10⁻³ bits per qubit sent, the greatest value among qubit-input channels reported so far.

量子通信线路的损耗会严重影响可靠信息传输的速率，通常被认为与状态无关。然而，损失概率通常取决于系统状态，极化相关损失是一个突出的例子。在这里，我们分析了为状态分配不同丢失概率的偏迹减少量子操作，并引入了广义擦除通道的概念。我们找到了广义擦除通道的经典和量子容量的下限和上限，并表征了其可降解性和抗降解性。我们揭示了在偏振相关损耗的情况下相干信息的超可加性，两字母量子容量和单字母量子容量之间的差异超过 7.197 10发送的每个量子位^-3位，这是迄今为止报告的量子位输入通道中的最大值。