Efficient Sympathetic Cooling of Neutral and Ionic Molecules for Quantum Information Processing

量子信息技术的目标是建立一个不以零和一操作的计算机处理器。相反，它将把数据保存在原子、离子或分子等量子系统的能级上。相对简单的分子是有利的候选者，因为这样的分子有足够的水平来编码所有的信息，但又不至于多到难以控制。然而，为了利用这种方法，分子必须在一个地方保持足够长的时间，以使它们在一个能级上做好准备，等待计算发生，然后再次读出信息。保持分子如此静止，几乎处于静止状态，是具有挑战性的，因为分子在室温下往往会剧烈地移动、振动和旋转。控制所有这些运动需要将分子冷却到较低的温度，仅比绝对零度高几度。这个项目将探索冷却分子的方法，从而准备它们的外部（运动）和内部（旋转和振动）状态，通过与慢速（“激光冷却”）原子的碰撞，可以作为一个冰箱来“同情冷却”分子。为了说明这种方法，项目的一部分将致力于计算原子和分子的能量景观，作为它们的分离，它们的方向和它们的内能态的函数。“非弹性”（内部状态改变）碰撞的概率也将被计算。总之，这些计算将帮助该研究小组分析制备超冷分子的不同方法的可行性。作为该项目的一部分，学生们还将接受培训，学习如何进行这些计算，以及如何评估这种超冷分子对量子技术的好处，为这一新兴领域的未来劳动力做好重要准备。几十年来，物理学家已经成功地用激光产生的力冷却和捕获简单的原子，使气体的温度降至接近绝对零度，例如使用光学糖蜜和磁光阱。然而，这些方法对分子的应用有限，因为分子缺乏循环转变。在这个项目中，首席研究员将从理论上研究一种新的冷却技术，通过与激光冷却原子的碰撞来操纵分子。特别是，在非弹性碰撞中，原子从分子中窃取能量，然后飞走，使分子内部和外部都变得更冷。该项目将依靠量子动力学计算和混合半经典散射模型来理解原子和分子的碰撞过程。我们特别感兴趣的是那些化学键由一个价电子主导的分子。它们都是极性的和顺磁性的，因此可以被电场和磁场操纵。这种分子的光学捕获阵列是无差错量子计算的候选系统。

The objective of quantum information technology is to build a computer processor that does not operate with zeros and ones. Instead, it will save data in the energy levels of quantum systems such as atoms, ions, or molecules. Relatively simple molecules are favorable candidates because such molecules have enough levels to encode all the information, but not so many as to make them difficult to control. To take advantage of this approach, however, molecules must be held in one place for long enough to prepare them in an energy level, wait for a computation to occur, and then read out the information again. Holding molecules so still, nearly at rest, is challenging because molecules at room temperature tend to vigorously move, vibrate, and rotate. Taming all of that movement requires that molecules to be chilled to a low temperature, just a fraction of a degree above absolute zero. This project will explore ways to cool molecules, and thereby prepare their external (motional) and internal (rotational and vibrational) states, by using collisions with slow ("laser cooled") atoms that can act as a refrigerator to "sympathetically cool" the molecules. To inform this approach, part of the project will be devoted to calculating the energy landscapes for atoms and molecules as a function of their separation, their orientation, and their internal energy states. The probabilities of "inelastic" (internal-state-changing) collisions will also be calculated. Together, these calculations will help this research team analyze the feasibility of different ways to prepare ultra-cold molecules. As part of this project, students will also receive training on how to perform these calculations and how to evaluate the benefits of such ultra-cold molecules for quantum technologies, important preparation for the future workforce in this emerging area. For several decades now, physicists have been successful in cooling and trapping simple atoms with laser-generated forces to get gasses down to temperatures near absolute zero, for example using optical molasses and magneto-optical traps. These approaches, however, have limited applications for molecules, because molecules lack a cycling transition. In this project, the principal investigator will theoretically study a novel cooling technique whereby molecules are manipulated by collisions with laser cooled atoms. In particular, in inelastic collisions, atoms steal energy from the molecule and then fly away leaving the molecule colder, both internally and externally. This project will rely on quantum dynamics calculations and hybrid semi-classical scattering models to understand the collision processes for atoms and molecules. Of particular interest are molecules with a chemical bond that is dominated by a single-valence electron. They are both polar and paramagnetic, and thus can be manipulated by electric and magnetic fields. An optically-trapped array of such molecules is a candidate system for error-free quantum computation.