单分子中的回声
Echo in a Single Molecule
摘要：
回声是一种普遍存在于许多物理系统中的现象，从磁场中的自旋到强子加速器中的粒子束。它通常在非均匀加宽的非线性物体集合中观察到，并用于消除环境引起的失相的影响，从而能够观察到适当的固有物体属性。在这里，我们报告的实验观察到的量子波包回波在一个单一的孤立分子。与常规回波相反，在这里，整个去相位-再相位循环发生在单个分子内，而没有分子特性的任何不均匀扩散，或与环境的任何相互作用。在我们的实验中，我们用短脉冲激光激发非简谐分子势中的振动波包，观察其随时间的振荡和最终色散。施加第二延迟脉冲激励，产生回波：初始相干波包的部分恢复。单分子的振动动力学是可视化的时间延迟探测脉冲解离他们一次一个。回声形成的两种机制进行了讨论：交流斯塔克诱导的分子势的动摇和创建的耗尽诱导的“洞”的核空间分布。观察并理论分析了振动波包的光致回波与量子回复之间的相互作用。单分子波包回波可能导致探测各种分子中超快分子内过程的新工具的发展。
英文摘要：
Echo is a ubiquitous phenomenon found in many physical systems, ranging from spins in magnetic fields to particle beams in hadron accelerators. It is typically observed in inhomogeneously broadened ensembles of nonlinear objects, and is used to eliminate the effects of environmental-induced dephasing, enabling observation of proper, inherent object properties. Here, we report experimental observation of quantum wave packet echoes in a single isolated molecule. In contrast to conventional echoes, here the entire dephasing-rephasing cycle occurs within a single molecule without any inhomogeneous spread of molecular properties, or any interaction with the environment. In our experiments, we use a short laser pulse to impulsively excite a vibrational wave packet in an anharmonic molecular potential, and observe its oscillations and eventual dispersion with time. A second delayed pulsed excitation is applied, giving rise to an echo: a partial recovery of the initial coherent wavepacket. The vibrational dynamics of single molecules is visualized by time-delayed probe pulse dissociating them one at a time. Two mechanisms for the echo formation are discussed: ac Stark-induced molecular potential shaking and creation of depletion-induced "hole" in the nuclear spatial distribution. Interplay between the optically induced echoes and quantum revivals of the vibrational wave packets is observed and theoretically analyzed. The single molecule wave packet echoes may lead to the development of new tools for probing ultrafast intramolecular processes in various molecules.
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