Branderhorst Matthijs P A, Londero Pablo, Wasylczyk Piotr, Brif Constantin, Kosut Robert L, Rabitz Herschel, Walmsley Ian A
Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, UK.
Science. 2008 May 2;320(5876):638-43. doi: 10.1126/science.1154576.
Manipulation of quantum interference requires that the system under control remains coherent, avoiding (or at least postponing) the phase randomization that can ensue from coupling to an uncontrolled environment. We show that closed-loop coherent control can be used to mitigate the rate of quantum dephasing in a gas-phase ensemble of potassium dimers (K2), which acts as a model system for testing the general concepts of controlling decoherence. Specifically, we adaptively shaped the light pulse used to prepare a vibrational wave packet in electronically excited K2, with the amplitude of quantum beats in the fluorescence signal used as an easily measured surrogate for the purpose of optimizing coherence. The optimal pulse increased the beat amplitude from below the noise level to well above it, and thereby increased the coherence life time as compared with the beats produced by a transform-limited pulse. Closed-loop methods can thus effectively identify states that are robust against dephasing without any previous information about the system-environment interaction.
对量子干涉的操控要求受控系统保持相干性，避免（或至少推迟）因与不受控环境耦合而可能产生的相位随机化。我们表明，闭环相干控制可用于减缓钾二聚体（K₂）气相系综中的量子退相干速率，该系综用作测试控制退相干一般概念的模型系统。具体而言，我们对用于在电子激发的K₂中制备振动波包的光脉冲进行自适应整形，将荧光信号中量子拍的幅度用作易于测量的替代量，以优化相干性。与变换极限脉冲产生的拍相比，最优脉冲将拍幅度从噪声水平以下提高到远高于该水平，从而延长了相干寿命。因此，闭环方法可以有效地识别对退相干具有鲁棒性的状态，而无需任何关于系统 - 环境相互作用的先验信息。
