Quantum queue-channels arise naturally in the context of buffering in quantum networks, wherein the noise suffered by the quantum states depends on the time spent waiting in the buffer. It has been shown that the upper-bound on the classical capacity of an additive queue-channel has a simple expression, and is achievable for the erasure and depolarizing channels [IEEE JSAIT, 1(2):432-444]. In this paper, we characterise the classical capacity for the class of unital qubit queue-channels, and show that a simple product (non-entangled) decoding strategy is capacity-achieving. As an intermediate result, we derive an explicit capacity achieving product decoding strategy for any i.i.d. unital qubit channel, which could be of independent interest. As an important special case, we also derive the capacity and optimal decoding strategies for a symmetric generalized amplitude damping (GAD) queue-channel. Our results provide useful insights towards designing practical quantum communication networks, and highlight the need to explicitly model the impact of buffering.
翻译:在量子网络缓冲的背景下,量子队列通道自然产生,量子队列受到的噪音取决于在缓冲中等待的时间。已经表明,一个添加式队列通道古典容量的上限是一个简单的表达方式,对于消化和分解渠道来说是可以实现的[IEEE JUSAIT, 1(2):432-444.4]。在本文中,我们描述了单子qubit队列通道类的古典能力,并表明一个简单的(非缠绕的)解码战略是能力实现。作为中间结果,我们产生了一种明确的实现任何i.i.d. 单子队列通道产品解码战略的能力,这种能力可能具有独立的兴趣。作为一个重要的特殊案例,我们还从一个对称通用缩排队列网(GAD)中获取了能力和最佳解码战略。我们的成果为设计实用的量子通信网络提供了有用的洞察力,并突出了明确模拟缓冲影响的必要性。