Sympathetic Cooling of Large Molecules in a Cold-Atom Trap

量子化学和计算化学现在可以高精度地确定甚至大分子的内能态。同样，分子动力学方法允许分子结构变化的时间和空间分辨视图，这可能发生在与外力场的相互作用之后。对这种变化的微观视图的实验访问通常限于分子强烈耦合的不受控制的环境中的系综平均值。我们项目的长期目标是在受控环境中解决单个大分子（大小为102-103道尔顿）内能态的随机发展。我们预计，如果在足够低的温度下将其在环境中保持足够长的时间，则可以检查聚集体的量子性质。在没有热碰撞的条件下，弱的长程力以及与热黑体背景的相互作用将控制孤立聚集体的时间发展。为了实现这样一个目标，我们将尝试识别和表征的结构，动力学和相干性的一个孤立的和冷的大分子，嵌入在一个被困的激光冷却的原子云，陷阱限制的平移运动，制冷剂原子和大分子。我们的目标是表征光谱量子签名，一旦大分子达到亚开尔文温度就会出现。通过这项研究，我们希望确定分子自由度与冷铷浴自由度之间的耦合，分子平移与内部自由度之间的耦合，在亚热能下从基态和激发态冷却剂原子到大分子的能量转移，以及冷却，加热，这一雄心勃勃的项目涉及若干子项目，其中一些子项目目前已经完成（见下文2.3），另一些子项目需要拟议项目的持续研究和支持（见下文3.3）。

Quantum chemistry and computational chemistry can nowadays determine to a high degree of precision internal energy states of even large molecules. Likewise molecular dynamics methods permit time- and space-resolved views of changes in molecular structure, which may occur following interaction with external force fields. Experimental access to microscopic views of such change is generally limited to ensemble averages in an uncontrolled environment to which the molecule is strongly coupled. The long term goal of our project aims at resolving the stochastic development of internal energy states of a single large molecule (size of 102-103 Dalton) in a controlled environment. We anticipate that the quantum nature of the aggregate can be examined, provided it is kept sufficiently long in an environment at sufficiently low temperature. Under such conditions when hot collisions are absent, weak long-range forces as well as the interaction with the thermal black-body background will control the temporal development of an isolated aggregate. In order to achieve such a goal we will attempt to identify and characterize the structural, dynamic, and coherence properties of an isolated and cold macromolecule, embedded in a trapped cloud of laser-cooled atoms, the trap confining the translational motion of both, refrigerant atoms and the macromolecule. We aim to characterize the spectral quantum signatures, which emerge once the macromolecule reaches sub-Kelvin temperatures. From this study, we hope to identify the stochastic cycles of coupling between molecular degrees of freedom and those of the cold rubidium bath, coupling between translation and the internal degrees of freedom of the molecule, energy-transfer from ground-and excitedstate coolant atoms to the macromolecule at sub-thermal energies, as well as the balance of cooling, heating, and clustering in the combined trap and the role of black-body radiation.This ambitious project entails several subprojects, some of which have by this time been completed (see below 2.3) and some which require ongoing research and support by the proposed project (see below 3.3).