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计算机处理器，不与0和1操作。相反，它将以原子、离子或分子等量子系统的能级保存数据。 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，但不会太多，使他们难以控制。 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，以便在一个能级上准备它们，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，因为室温下的分子往往会剧烈运动，振动和旋转。 驯服所有这些运动需要将分子冷却到低温，仅比绝对零度高几度。该项目将探索冷却分子的方法，从而通过使用与慢（“激光冷却”）原子的碰撞来准备它们的外部（运动）和内部（旋转和振动）状态，这些原子可以作为冰箱来“同情地冷却”分子。为了告知这种方法，该项目的一部分将致力于计算原子和分子的能量景观，作为其分离，方向和内部能量状态的函数。“非弹性”（内部状态变化）碰撞的概率也将被计算。总之，这些计算将帮助该研究团队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，学生还将接受如何执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的培训，这是为这一新兴领域未来劳动力的重要准备。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。 特别令人感兴趣的是那些化学键由一个单价电子控制的分子，它们既有极性又有顺磁性，因此可以被电场和磁场操纵。这种分子的光阱阵列是无误差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.