标题： 量子成本高效的方案，违反霍尔沃夫界限并在存在戴维斯封闭类时序曲线的情况下进行克隆 显示英文标题

标题： Quantum Cost Efficient Scheme for Violating the Holevo Bound and Cloning in the Presence of Deutschian Closed Timelike Curves

摘要： Brun \emph{等人} [Phys. Rev. Lett. \textbf{102}, 210402 (2009)] 表明，在存在 Deutschian 闭类时曲线（D-CTC）的情况下，可以违反 Holevo 界。 可以利用 Holevo 界的违反，在一个量子比特中编码$n$-位经典信息。 在这里，我们展示了一种新的量子成本高效的方案，在违反 Holevo 界的情况下，能够在 D-CTC 存在时忠实存储和检索$n$-位经典信息。 我们还提出了一种在 D-CTC 存在下克隆量子比特的新协议。 在这两种方案中，量子成本被发现是$O(n)$的数量级，这比现有具有指数级量子成本的方案具有优势。 显示英文摘要

摘要： Brun \emph{et al.} [Phys. Rev. Lett. \textbf{102}, 210402 (2009)] showed that in the presence of a Deutschian closed timelike curve (D-CTC), one could violate the Holevo bound. It is possible to utilize the Holevo bound violation to encode $n$-bit classical information in a single qubit. Here we demonstrate a new quantum cost efficient scheme, for storing and retrieving $n$-bit classical information faithfully in the presence of a D-CTC in violation of the Holevo bound. We also propose a new protocol for cloning a qubit in the presence of a D-CTC. In both the schemes, the quantum cost is found to be of order $O(n)$, which provides an advantage over the existing schemes having quantum cost of exponential order.