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arXiv quant-ph/0308168quant-ph
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关于任意约束通道的可加性猜想

On the additivity conjecture for channels with arbitrary constraints

M. E. Shirokov

摘要:

最近Shor证明了几个与Holevo容量和形成纠缠有关的开放(子)可加性问题的等价性[15]。在我们之前的注释[6]中,这些等价于具有任意线性约束的信道的Holevo容量的可加性。本说明是前一个在一般约束通道方向上的发展。引入输入约束提供了更大的灵活性,在治疗的可加性猜想。考虑了任意约束信道的Holevo容量,导出了该信道的最优系综的特征性质,推广了Schumacher和Westmoreland的最大距离性质(命题1).它表明,两个通道与单一的线性约束的可加性猜想是等价的两个任意约束的通道,因此,一个有趣的次加性性质的$χ$ -功能的张量积这些通道(定理1)的类似猜想。我们还提出了另一种方法来证明任何两个无约束通道的可加性猜想意味着形成纠缠的强超可加性。从凸分析的参数提供了另一个表征通道的次加性的$χ$ -功能保持(定理3)。Shor的通道扩展的这种表征和一些修改提供了一种简单的方法来证明无约束通道的最小输出熵的全局可加性意味着$χ$ -函数的全局次可加性和形成纠缠的强超可加性。

英文摘要:

Recently Shor proved equivalence of several open (sub)additivity problems related to the Holevo capacity and the entanglement of formation [15]. In our previous note [6] equivalence of these to the additivity of the Holevo capacity for channels with arbitrary linear constraints was shown. This note is the development of the previous one in the direction of channels with general constraints. Introducing input constraints provides greater flexibility in the treatment of the additivity conjecture. The Holevo capacity of arbitrarily constrained channel is considered and the characteristic property of an optimal ensemble for such channel is derived, generalizing the maximal distance property of Schumacher and Westmoreland (proposition 1). It is shown that the additivity conjecture for two channels with single linear constraints is equivalent to the similar conjecture for two arbitrarily constrained channels and, hence, to an interesting subadditivity property of the $χ$-function for the tensor product of these channels (theorem 1). We also propose an alternative way of proving that the additivity conjecture for any two unconstrained channels implies strong superadditivity of the entanglement of formation. The arguments from the convex analysis provide another characterization of channels for which subadditivity of the $χ$-function holds (theorem 3). This characterization and some modification of Shor's channel extension provide a simple way of proving that global additivity of the minimum output entropy for unconstrained channels implies global subadditivity of the $χ$-function and strong superadditivity of the entanglement of formation.

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