Sympathetic Cooling of Large Molecules in a Cold-Atom Trap

如今，量子化学和计算化学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对分子结构的变化进行时间和空间分辨，这些变化可能在与外力场相互作用后发生。对这种变化进行微观观察的实验通常限于在分子与之强耦合的不受控制的环境中的总体平均值。我们项目的长期目标是解决单个大分子（大小为102-103道尔顿）在受控环境中内能态的随机发展。我们预计，如果聚集体在足够低的温度下保持足够长的时间，就可以检查其量子性质。在不存在热碰撞的条件下，弱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。为了实现这一目标，我们将尝试识别和表征一个孤立的冷大分子的结构、动力学和相干性，它被嵌入在激光冷却原子的陷阱云中，这个陷阱限制了冷媒原子和大分子的平移运动。我们的目标是描述光谱量子特征，一旦大分子达到亚开尔文温度就会出现。从这项研究中，我们希望确定分子自由度与冷铷浴之间耦合的随机循环，分子平移与内部自由度之间的耦合，从基态和激发态冷却剂原子到亚热能量的大分子的能量传递，以及联合阱中冷却，加热和聚集的平衡以及黑体辐射的作用。这个雄心勃勃的项目包括几个子项目，其中一些到目前为止已经完成（见下文2.3），还有一些需要拟议项目进行研究和支持（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).