Molecular Quantum Control by Coherence Effects

这个项目将使用激光来控制分子，即化学结合在一起的原子。 通常需要至少两个电子才能在原子之间建立化学键。这些电子的自旋可以是平行的（三重态）或反平行的（单重态）。该项目将使用激光在单重态和三重态之间切换分子，从而实现具有量子计算潜在应用的“自旋开关”。此外，该项目还将研究在明确定义的初始条件下原子和分子的碰撞。一般来说，分子不是球对称的物体，因此大多数涉及它们的碰撞过程强烈依赖于碰撞伙伴的相对排列。该项目将使用激光来控制这种对准。理解原子和分子之间碰撞过程的基本物理对于化学反应等过程具有重要意义。由于耦合导致的量子态特征的混合取决于相互作用的强度以及相互作用量子态之间的能量分离。利用强控制激光的交流斯塔克效应使锂二聚体的自旋-轨道耦合振转能级对的能级发生共振，在外加光场的影响下，单重态和三重态之间的布居转移将在时域内以受控的方式发生。当两个状态处于共振状态（具有相同的能量）时，概率函数具有振荡时间依赖性，其周期与两个状态的耦合强度成反比。因此，如果种群最初被置于其中一个状态，并且两个状态仅在半整数振荡周期的持续时间内迅速进入共振，然后迅速脱离共振，则种群将有效地从其中一个状态切换到另一个状态。控制激光的电场幅度由两个态的共振条件决定，脉冲宽度由它们的振荡周期决定。碱金属分子和惰性气体原子之间的碰撞的动力学和动力学将在定义明确的初始条件下使用控制激光器的AC斯塔克效应创建的分子排列进行研究。取向将通过使用跃迁偶极矩的取向依赖性去除磁子能级的简并来实现。磁子能级是分子的总角动量在实验室固定轴上的投影，该轴由共振激光场的偏振方向定义。对于足够大的控制激光拉比频率，子能级将被足够好地分离，因此可以探测一个或多个旋转量子态的分子的特定量子化取向，并研究它们之间的碰撞转移。这种方法的优点在于，与使用外部磁场或电场的情况相比，它将允许选择性地去除磁子级简并。

This project will use laser light to control molecules, atoms that are chemically bound together. Typically it takes at least two electrons to create a chemical bond between atoms. The spins of these electrons can be parallel (triplet states) or antiparallel (singlet states). This project will use laser light to switch the molecule between a singlet and a triplet state, thus realizing a "spin switch" with potential applications to quantum computing. Additionally, this project will study the collisions of atoms and molecules under well-defined initial conditions. In general, molecules are not spherically symmetric objects and as a result most collisional processes involving them strongly depend on the relative alignment of the colliding partners. This project will use lasers to control this alignment. Understanding the basic physics of collision processes between atoms and molecules is of importance for processes such as chemical reactivity. The mixing of the character of quantum states due to coupling depends on the strength of the interaction as well as on the energy separation between the interacting quantum states. Using the AC Stark effect of a strong control laser to shift the energy levels of a spin-orbit coupled pair of ro-vibrational levels of the Lithium dimer into resonance, the population transfer between a singlet and a triplet state would occur in a controlled fashion in the time domain under the influence of an external optical field. When two states are on resonance (have the same energy) the probability function has an oscillatory time dependence with a period inversely proportional to the coupling strength of the two states. Thus, if the population is initially placed in one of the states and the two states are rapidly brought into resonance only for the duration of half integer oscillatory periods, and then rapidly moved off resonance, the population will effectively switch from one of the states to the other one. The electric field amplitude of the control laser is determined by the resonance condition of the two states, and the pulse duration by their oscillatory period. The kinetics and dynamics of collisions between alkali molecules and noble gas atoms will be studied under well-defined initial conditions of molecular alignment created using the AC Stark effect of a control laser. The orientation will be achieved by removing the degeneracy of the magnetic sublevels using the orientation dependence of the transition dipole moment. The magnetic sublevels are projections of the total angular momentum of the molecule on a laboratory fixed axis defined by the polarization direction of the resonant laser field. For sufficiently large control laser Rabi frequencies, the sublevels will be separated well enough so specific quantized orientations of the molecules of one or more rotational quantum states can be probed and the collisional transfer between them studied. An advantage of this method is that it will allow for selective removal of the magnetic sublevel degeneracy in contrast to cases where external magnetic or electric fields are used.