基于自旋系统混合量子体系中的态传输研究

The Heisenberg spin system has proved to be a useful and effective model for realizing robust quantum state transfer. Theoretical studies have shown that, in principle, perfect state transfer can be achieved when couplings are properly configured. To date, two configurations have been found that permit perfect state transfer. Noise will be present in any experiment, therefore it is important to study, characterize, and compare the effects of realistic noise processes between various communication schemes. For example, a perfect state transfer protocol may set the bar in the idealized setting, but may perform worse than a "good" state transfer protocol when noise is taken into account. We aim to address questions such as these as we investigate the fidelity of state transfer resulting from a diverse array of coupling configurations that satisfy the symmetric distribution. For each of these configurations, we propose to outline a procedure that can be taken to test our theoretical predictions in the laboratory. Furthermore, we propose to devise schemes for reducing the noise effects which will inevetibly emerge in an experimental realization. Finally, we will study the state and heat transfer in a hybrid structure where a spin chain interacts with two reservoirs as well as the information exchange which occcurs between the environment and the chain. We will primarily focus on facets associated with practical quantum communication -fruitful results can be obtained by addressing the practicality of an emerging technology.

海森堡自旋系统是量子计算装置内部进行高质量量子通信的有效载体，如何在自旋系统中实现完美的态传输已有系统而深入的研究。本项目以自旋系统中两种耦合位形能产生完美的态传输为基础，探讨实验上实现理论要求的耦合强度分布的方案，研究各种对称性耦合分布下的传输保真度。在此基础上，研究自旋系统各种不同物理实现所面临的不同噪声对通信的影响并进一步提出减弱噪声影响的方案。另外，考虑自旋系统与热库连接所构成的混合量子体系中的态传输及热传输问题，研究热库与自旋系统之间的信息交换。本项目的研究内容将解决量子通信所面临的一些实际问题，这对于最终实现微观量子器件内部短距离通信具有重要的理论意义和实用价值。

近年来，利用海森堡自旋链进行量子通信得到了广泛而深入的研究。本项目主要研究基于自旋系统的混合量子体系中的量子态传输，重点探讨了一个自旋链的两端与外部两个热库相互作用的模型。重要结果如下（1）对外部存在两个非马尔科夫的热库模型，利用QSD方程方法计算了保真度随时间演化。我们发现环境的非马尔科夫性会使得保真度得以提高。（2）研究了噪声条件下绝热和非绝热的量子态传输问题。我们发现“绝热过程的捷径”也能适用于非绝热的控制路径，例如非绝热的量子态传输过程。通过施加有效的外部控制，能够有效实现量子态传输。（3）研究了实验室坐标系下的绝热泄露消除算符实现问题。通过在绝热基下面外加一个泄露消除算符，我们可以抑制绝热过程中不同瞬时本征态之间的交叉问题，从而实现了系统的绝热加速。上述研究成果对实现噪声条件下绝热量子计算，绝热量子通信有重要的理论意义。