In this article, we analyse the relationship between the Bell violation and the secure key rate of entanglement assisted quantum key distribution (QKD) protocols. Specifically, we address the question whether Bell violation is necessary or sufficient for secure communication. We construct a class of states which do not show Bell violation, however, which can be used for secure communication after local filtering. Similarly, we identify another class of states which show Bell violation but can not be used for generating secure key even after local filtering. The existence of these two classes of states demonstrates that Bell violation as an initial resource is neither necessary nor sufficient for QKD. Our work therefore forces a departure from traditional thinking that the degree of Bell violation is a key resource for quantum communication and brings out the role of local filtering.

中文翻译：

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Bell-CHSH违规和局部过滤在量子密钥分发中的作用

在本文中，我们分析了贝尔违规与纠缠辅助量子密钥分发 (QKD) 协议的安全密钥率之间的关系。具体来说，我们解决了贝尔违规对于安全通信是否必要或充分的问题。然而，我们构造了一类不显示贝尔违规的状态，可用于本地过滤后的安全通信。类似地，我们确定了另一类显示 Bell 违规但即使经过本地过滤也不能用于生成安全密钥的状态。这两类状态的存在表明，贝尔违规作为初始资源对于 QKD 既不必要也不充分。