Engineering Polyatomic Molecules with Optical Cycling Centers for Quantum Science Applications

激光冷却和俘获原子使原子和分子物理学发生了革命性的变化，并导致了几个科学和技术学科的突破。这些进展使新一代原子钟、物质奇异相的模拟、高灵敏度传感器的开发以及基于原子的量子信息科学得以实现。激光冷却原子也使超冷、亚微开尔文双原子分子样品的组装成为可能，这些样品足够致密，以至于量子简并效应变得重要。这些分子受到电场和磁场以及光学陷阱或镊子的限制，在那里它们与环境隔离，可以进行仔细的研究。用更大的多原子分子实现类似的控制仍然具有挑战性。这种分子有更复杂的电子、振动和弯曲运动，能量可能会在不经意间转移到这些运动中。那么，是否存在成功激光冷却所需的近乎封闭的光学循环转变的多原子分子就远不明显了。然后，这些跃迁可以重复地散射光子，这样分子质心的运动就可以冷却到毫开尔文或更小的等值动能以下。确实存在一系列多原子分子独有的有前途的应用。这包括进行精密光谱测试粒子物理的标准模型，以及令人兴奋的是，由于每个超冷分子都可以在独特的振动状态下制备，因此有望对化学反应进行量子控制。由于分子的De-Broglie波长远大于分子间作用力的范围，因此断裂和建立化学键的动力学将更加有趣。这个项目将提高对“相对简单”的三原子分子M-OH的电子和振动结构的理解，其中金属阳离子M是碱土或稀土原子。它们在金属阳离子上有一个有用的光学循环跃迁。然后，研究人员将研究用更大的配体或分子链取代M-OH中的氢原子的效果。将具有循环跃迁的碱土或稀土原子添加到未来的多原子分子中是另一个研究方向。在任何一种方法中，金属阳离子的价电子都不应该受到明显的干扰，光学循环和冷却仍然是可能的。最终的梦想是设计出具有不止一个光学循环中心的多原子分子。从科学上讲，这项研究将促进对金属-配体偶联的理解，并阐明分子复杂性对Franck-Condon因子对角特性的作用，Franck-Condon因子是衡量光学循环跃迁质量的定量指标。势能面的形状将被描述为原子几何，其中所有原子彼此接近，并且在可行的情况下，在更多原子中的一个已经解离并远离的地方。研究人员将定位它们的极小点、鞍点以及圆锥形交点，在那里，相同电子对称的两个势面接触。还将研究接近线性几何构型的M-OH三聚体的Renner-Teller效应。这项工作由物理部的理论原子、分子和光学物理计划和量子信息科学计划以及化学部的化学理论、模型和计算方法计划共同支持。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Laser cooling and trapping of atoms has revolutionized atomic and molecular physics and led to breakthroughs in several disciplines of science and technology. The advances enabled a novel generation of atomic clocks, simulation of exotic phases of matter, the development of highly-sensitive sensors, and atom-based quantum information science. Laser cooling of atoms has also made possible the assembly of ultracold, sub microkelvin diatomic molecular samples that are sufficiently dense for quantum degeneracy effects to be important. These molecules are confined by electric and magnetic fields as well as optical traps or tweezers, where they are isolated from their environment and can be carefully studied. Achieving similar control with larger polyatomic molecules remains challenging. Such molecules have more complex electronic, vibrational, and bending motion into which energy can be inadvertently transferred. It is then far from obvious whether there exist polyatomic molecules with a nearly-closed optical cycling transition needed for successful laser cooling. These transitions can then repeatedly scatter photons so that the molecular center-of-mass motion can be cooled below a milli-Kelvin or less equivalent kinetic energy. A list of promising applications unique to polyatomic molecules does exist. This includes performing precision spectroscopy to test the Standard Model of particle physics, and, excitingly, the promise of quantum control of chemical reactions as each ultracold molecule can be prepared in a unique vibrational state. As the de-Broglie wavelength of the molecules is much larger than the range of intermolecular forces, the dynamics of the breaking and making chemical bonds promises to be even more interesting.This project will improve understanding of the electronic and vibrational structure of the "relatively-simple" triatomic molecules M-OH, where the metal-cation M is an alkaline-earth or rare-earth atom. They have a usable optical cycling transition located on the metal cation. The researchers will then study the effect of replacing the hydrogen atom in M-OH by a larger ligand or chains of molecules. Adding alkaline-earth or rare-earth atoms with their cycling transitions to prospective polyatomic molecules is another research direction. In either approach the valence electron of the metal-cation should not be significantly disturbed, and optical cycling and cooling might remain possible. The ultimate dream is to design polyatomic molecules with more than one optical cycling center. Scientifically, the research will advance understanding of metal-ligand couplings and elucidate the role of molecular complexity on the diagonal character of Franck-Condon factors, the quantitative measure for the quality of optical cycling transitions. The shape of potential energy surfaces will be characterized for atomic geometries, where all atoms are close to each other and, when feasible, where one of more atoms has dissociated and is far away. The researchers will locate their minima, saddle points as well as conical intersections, where two potential surfaces of the same electron symmetry touch. Renner-Teller effects will also be studied for the M-OH trimer near linear geometries. This work is jointly supported by the Theoretical Atomic, Molecular and Optical Physics Program and the Quantum Information Science Program within the Division of Physics, as well as by the Chemical Theory, Models and Computational Methods Program in the Division of Chemistry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.