发表机构
Cornell University（康奈尔大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文证明了纯损耗玻色子信道在无约束量子容量下的强逆定理，通过结合量子检验不等式和平衡信道方差界，确保高于容量时保真度随信道使用次数倒数衰减。
AI 中文摘要
本文报告了无约束量子容量下纯损耗玻色子信道的强逆定理的证明。在高于容量的每个固定速率下，每个码的纠缠生成保真度被限制为信道使用次数的倒数乘以一个常数。该界限在无能量约束下成立，并适用于任意编码态，包括跨所有输入模式相关的态，以及任意联合解码器。证明结合了量子切比雪夫不等式和曲棍球棒检验不等式，以及对应于透射率 $\eta=1/2$ 的平衡纯损耗信道的均匀相对熵方差界。方差界通过将平衡分束器表示为亮模式和暗模式得出：暗模式恰好处于真空态，而任何与该真空态正交的态至少包含一个暗光子。对于一般透射率，通过膨胀退化衰减器将问题简化为平衡信道设置，并将解码器检验精确地限制为产生已知量子容量阈值的因子。由此得到的论证为每个纯损耗玻色子信道建立了无约束量子容量下的强逆定理。
英文摘要
This paper reports the proof of a strong converse for the unconstrained quantum capacity of the pure-loss bosonic channel. At every fixed rate above capacity, the entanglement-generation fidelity of every code is bounded by a constant times the reciprocal of the number of channel uses. The bound holds without an energy constraint and for arbitrary encoded states, including states correlated across all input modes, and arbitrary joint decoders. The proof combines quantum Chebyshev and hockey-stick testing inequalities with a uniform relative-entropy-variance bound for the balanced pure-loss channel, corresponding to transmissivity $η=1/2$. The variance bound follows by expressing the balanced beam splitter in bright and dark modes: the dark modes are exactly in vacuum, and any state orthogonal to that vacuum contains at least one dark photon. For general transmissivity, dilating the degrading attenuator reduces the problem to this balanced-channel setting and bounds the decoder test by precisely the factor that produces the known quantum-capacity threshold. The resulting argument establishes the strong converse at the unconstrained quantum capacity for every pure-loss bosonic channel.
Comments26 pages, 1 figure
