Information-theoretic techniques are based on the assumption that resources are well characterized by independent and identically distributed (iid) states. This assumption cannot be justified operationally, since, for example, correlations between subsequent systems emitted by a source cannot be detected by any practical tomographic protocol. Operationally motivated symmetry assumptions still imply, via de Finetti theorems, that the resources are described by almost-iid states. This raises the question: Are almost-iid resources as effective as perfect iid resources for information-processing tasks? Here we address this question and prove that the conditional entropy of almost-iid states asymptotically coincides with that of iid states. As an application, this implies that squashed entanglement is robust for almost-iid states, asymptotically matching its value on iid states.

翻译：信息论技术通常基于资源可由独立同分布状态充分表征的假设。这一假设在操作层面无法得到验证，例如，源发射的连续系统间的关联性无法通过任何实际的层析成像协议检测。基于操作动机的对称性假设，通过德菲内蒂定理仍可推导出资源由近乎独立同分布状态描述。这引出一个核心问题：近乎独立同分布资源在信息处理任务中是否与完美独立同分布资源同样有效？本文针对该问题展开研究，证明了近乎独立同分布状态的条件熵在渐近意义上与独立同分布状态的条件熵一致。作为应用，该结论表明压缩纠缠在近乎独立同分布状态下具有鲁棒性，其渐近值与独立同分布状态下的值相符。