Formation, Dynamics and Application of Ultracold Molecules

现代物理学的本质是量子力学。特别是原子核和周围电子的结构，以及分子和材料的相应结构，本质上是量子力学的。理解原子、分子和材料在室温或更高温度下的量子结构，其中有数千或数百万或更多的量子态，可以使用激光的选择性。然而，在低于0.001 K的超冷温度下，只有少数量子态被填充，并且像超流体和许多粒子的玻色-爱因斯坦凝聚这样的奇异现象是可能的，每个粒子都处于一个独特的量子态。这项研究涉及了解由两个原子组成的简单分子在超冷温度下的量子态，包括分子如何在特定的可选择状态下形成，以及分子在暴露于特定波长的光或与其他分子或原子碰撞时如何变化。作为回应，它们可能会发光、发射电子或分裂成两个原子。这种行为有许多有趣的可能应用，如量子密码学、量子计算和更复杂系统的量子模拟。这一前沿研究领域为物理学和相关领域的学生提供了一个未知的和具有挑战性的教育。在我们的项目中，我们将使用两个精心挑选的双原子分子，Rb2和KRb。在这两个分子中都有一个令人着迷的电子量子态是三重态。这种状态原则上可以衰减，但对Rb2的计算预测，它在最低的旋转振动水平上有长达200秒的寿命，在此期间可以对其进行研究。我们的实验将确定由于自发光发射或与超冷原子或分子碰撞而导致的超冷温度下这种“亚稳态”的极限。我们还将研究这些分子中另一种令人着迷的电子量子态：所谓的“三叶虫”或“蝴蝶”电子量子态，在这种电子量子态中，一种全新的化学键发生在核间距离至少比普通化学键大十倍的地方。它们的名字来自于电子波函数平方的复杂空间结构，它可以像古代的三叶虫或现代的蝴蝶。这种新型的键合涉及到高度激发的里德伯原子的电子与嵌入在大里德伯电子波函数中的第二个基态原子之间的吸引力。光谱学将确定预测的和不寻常的“原子间过山车”势能曲线，具有许多最大值和最小值，以及确定这些状态寿命的多个衰变过程。特别是，将确定这些态以令人费解的速度衰变为（Rb2）阳离子和负电子的机制。我们还将研究由离子对（Rb正离子和Rb阴离子）产生的远程电子态，其中一些与“蝴蝶”态处于相同的能量和核间距离区域。这些都是“重里德伯”态，和氢原子一样受到库仑引力的束缚。离子对实验将提供有关较短距离共价态（成键电子共享）与较长距离离子态（两个价电子明显位于其中一个原子上）耦合的宝贵信息。

The essence of modern Physics is quantum mechanics. In particular, the structure of the atomic nucleus and the surrounding electrons, and the corresponding structure of molecules and materials is inherently quantum mechanical. Understanding the quantum structure of atoms, molecules, and materials at room temperature and higher, where thousands or millions or more quantum states are populated, is possible using the selectivity of lasers. However, at ultracold temperatures of less than 0.001 K, only a few quantum states are populated and exotic phenomena such as superfluidity and Bose-Einstein condensation of many particles, each in a single unique quantum state are possible. This research involves understanding the quantum states of simple molecules composed of two atoms at ultracold temperatures, including how the molecules are formed in particular selectable states and how the molecules change when they are exposed to light of specific wavelengths or collide with other molecules or atoms. In response, they may emit light, emit an electron, or split into two atoms. There are a number of interesting possible applications of this behavior such as quantum cryptography, quantum computing and quantum simulation of more complex systems. This area of frontier research provides an uncharted and challenging education for students in Physics and related fields.In our project, we will work with two carefully selected diatomic molecules, Rb2 and KRb. One fascinating electronic quantum state in both molecules is the triplet state. This state can in principle decay, but calculations for Rb2 predict it has a very long lifetime of up to 200 seconds in its lowest rovibrational level, during which it can be studied. Our experiments will define the limits of this "metastability" at ultracold temperatures due to spontaneous emission of light or to collisions with ultracold atoms or molecules. We will also study another fascinating type of electronic quantum state in these molecules: the so-called "trilobite-like" or "butterfly" electronic quantum states, where a completely new kind of chemical bonding takes place at internuclear distances at least ten times larger than ordinary chemical bonds. Their name comes from the complex spatial structures of the square of the electronic wavefunction, which can resemble ancient trilobites or modern butterflies. This novel bonding involves the attraction between the electron of a highly excited "Rydberg" atom with a second ground state atom imbedded within the large Rydberg electronic wavefunction. Spectroscopy will determine the predicted and unusual "interatomic roller coaster" potential energy curves with numerous maxima and minima, as well as the multiple decay processes that determine lifetimes of these states. In particular, the mechanisms of the puzzlingly rapid rates of decay of these states to (Rb2) cation and the negative electron will be determined. We will also investigate the long-range electronic states arising from the ion-pair (Rb cation and Rb anion), some in the same region of energy and internuclear distance as the "butterfly" states. These are "Heavy Rydberg" states, bound by the Coulomb attraction in the same way as in the H atom. The ion pair experiments will yield valuable information on the coupling of shorter range covalent states, where the bonding electrons are shared, to the longer range ionic states, where the two valence electrons clearly reside on one of the atoms.