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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Boundary of quantum evolution under decoherence
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Boundary of quantum evolution under decoherence

机译：退相干下的量子演化边界

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摘要

Relaxation effects impose fundamental limitations on our ability to coherently control quantum mechanical phenomena. In this article, we use principles of optimal control theory to establish physical limits on how closely a quantum mechanical system can be steered to a desired target state in the presence of relaxation. In particular, we explicitly compute the maximum amplitude of coherence or polarization that can be transferred between coupled hetero-nuclear spins in large molecules at high magnetic fields in the presence of relaxation. Very general decoherence mechanisms that include cross-correlated relaxation have been included in our analysis. We give analytical characterization for the pulse sequences (control laws) that achieve these physical limits and provide supporting experimental evidence. Exploitation of cross-correlation effects has recently led to the development of powerful methods in NMR spectroscopy to study very large biomolecules in solution. For two heteronuclear spins, we demonstrate with experiments that cross-correlated relaxation optimized pulse (CROP) sequences provide significant gains over the state-of-the-art methods. It is shown that despite large relaxation rates, coherence can be transferred between coupled spins without any loss in special cases where cross-correlated relaxation rates can be tuned to autocorrelated relaxation rates.
机译：弛豫效应对我们一致地控制量子力学现象的能力施加了根本限制。在本文中，我们使用最佳控制理论的原理来建立物理限制，以了解在存在弛豫的情况下量子力学系统可如何紧密地转向所需的目标状态。特别是，我们明确地计算了在高磁场下存在弛豫的情况下，大分子中耦合的异核自旋之间可以转移的相干或极化的最大幅度。我们的分析中包括非常通用的退相干机制，其中包括互相关松弛。我们对达到这些物理极限并提供支持实验证据的脉冲序列（控制律）进行了分析表征。利用互相关效应最近导致了NMR光谱学中强大的方法的发展，以研究溶液中非常大的生物分子。对于两个异核自旋，我们通过实验证明了互相关的弛豫优化脉冲（CROP）序列提供了超过最新技术的显着收益。结果表明，尽管弛豫速率较大，但在互相关弛豫速率可以调整为自相关弛豫速率的特殊情况下，相干可以在耦合自旋之间转移而没有任何损失。

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