态变换的量子控制理论：暗态及其启示
Quantum Control Theory for State Transformations: Dark States and their Enlightenment
摘要：
对于许多量子信息协议，如状态传输、纠缠传输和纠缠产生，量子系统的标准可控性概念太强。我们引入了较弱的概念，可访问对，并证明了一个上限上的一对状态之间的变换的对称性的基础上实现的保真度。提出了一个大类的自旋网络，这个界限可以饱和。在这种情况下，我们将展示如何计算一个给定的激发保持演化的不可访问的暗态，并说明如何使用额外的催化激发访问其中的一些。这强调了自旋网络中状态转移的分析仅限于单激发子空间是不够的。在这些自旋网络中的一类对称性是完全特征的基本图形属性。
英文摘要：
For many quantum information protocols such as state transfer, entanglement transfer and entanglement generation, standard notions of controllability for quantum systems are too strong. We introduce the weaker notion of accessible pairs, and prove an upper bound on the achievable fidelity of a transformation between a pair of states based on the symmetries of the system. A large class of spin networks is presented for which this bound can be saturated. In this context, we show how the inaccessible dark states for a given excitation-preserving evolution can be calculated, and illustrate how some of these can be accessed using extra catalytic excitations. This emphasises that it is not sufficient for analyses of state transfer in spin networks to restrict to the single excitation subspace. One class of symmetries in these spin networks is exactly characterised in terms of the underlying graph properties.
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