If a measurement is made on one half of a bipartite system, then, conditioned on the outcome, the other half has a new reduced state. If these reduced states defy classical explanation-that is, if shared randomness cannot produce these reduced states for all possible measurements-the bipartite state is said to be steerable. Determining which states are steerable is a challenging problem even for low dimensions. In the case of two-qubit systems a criterion is known for T-states (that is, those with maximally mixed marginals) under projective measurements. In the current work we introduce the concept of keyring models-a special class of local hidden state models. When the measurements made correspond to real projectors, these allow us to study steerability beyond T-states. Using keyring models, we completely solve the steering problem for real projective measurements when the state arises from mixing a pure two-qubit state with uniform noise. We also give a partial solution in the case when the uniform noise is replaced by independent depolarizing channels.

中文翻译：

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钥匙圈模型：一种实现可操纵性的方法

如果对二分系统的一半进行测量，则根据结果，另一半具有新的减少状态。如果这些简化状态无视经典解释——也就是说，如果共享随机性不能为所有可能的测量产生这些简化状态——那么二分状态就被称为是可控的。即使对于低维，确定哪些状态是可操纵的也是一个具有挑战性的问题。在双量子位系统的情况下，投影测量下的 T 状态（即具有最大混合边缘的那些）的标准是已知的。在当前的工作中，我们引入了密钥环模型的概念——一种特殊的局部隐藏状态模型。当测量结果与真实投影仪相符时，我们就可以研究超出 T 状态的可操纵性。使用钥匙圈模型，当状态是由纯双量子位状态与均匀噪声混合而产生时，我们完全解决了真实投影测量的转向问题。当均匀噪声被独立的去极化通道代替时，我们也给出了部分解决方案。