存在各向同性退相干时的Uhlmann几何相位
Uhlmann's geometric phase in presence of isotropic decoherence
摘要：
Uhlmann的混合态几何相位[Rep. Math. Phys. { \bf 24}，229（1986）]是在一个量子位受各向同性退相干影响的情况下，在马尔可夫近似处理分析。结果表明，该相位随退相干速率的增加而迅速减小，对于纯或近纯初态，该相位对弱退相干最为脆弱。在单一的情况下，我们比较乌尔曼的几何相位的混合状态与发生在标准马赫-曾德尔干涉[物理评论快报。{ \bf 85}，2845（2000）]，并表明后者对Bloch向量长度的减少更鲁棒。我们还描述了如何乌尔曼的几何相位在目前的情况下，原则上可以实现实验。
英文摘要：
Uhlmann's mixed state geometric phase [Rep. Math. Phys. {\bf 24}, 229 (1986)] is analyzed in the case of a qubit affected by isotropic decoherence treated in the Markovian approximation. It is demonstrated that this phase decreases rapidly with increasing decoherence rate and that it is most fragile to weak decoherence for pure or nearly pure initial states. In the unitary case, we compare Uhlmann's geometric phase for mixed states with that occurring in standard Mach-Zehnder interferometry [Phys. Rev. Lett. {\bf 85}, 2845 (2000)] and show that the latter is more robust to reduction in the length of the Bloch vector. We also describe how Uhlmann's geometric phase in the present case could in principle be realized experimentally.
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