Coherent Control and Precision Spectroscopy of a Polyatomic Molecular Ion

这个项目的动机是有机会实现对单个多原子分子量子态的相干控制，并利用这种控制进行精确测量。该项目将重点关注捕获和控制分子离子N_2H+，但该方法可以推广到许多其他分子离子。N_2H+分子离子将与钙离子共同被捕获和冷却到接近它们共同运动的基态。然后，分子离子的纯量子态可以通过使用量子逻辑光谱的投影测量来初始化，正如研究人员最近在氢化钙离子CaH+上所证明的那样。这很重要，因为这种方法可以推进量子化学，并可能影响材料科学以及化学、生物和制药行业。此外，用于天文观测的新的和更好的参考光谱可以更好地理解星际气体云和宇宙，包括对超出标准模型的严格物理测试。最终，在量子水平上控制分子可以实现精确的协调碰撞和完全控制的量子化学。虽然双原子分子的激光冷却、俘获和精确测量取得了巨大的进展，但多原子分子由于其复杂的能级结构和大量的填充态而难以进行精确研究。本项目将扩展量子逻辑光谱技术，以制备多原子分子的纯量子态，并在多普勒或压力位移等最小扰动下操纵和检测其状态。精密光谱学最终将只受状态寿命的限制，因此可以被推到以前只有光学原子钟才能达到的水平。N_2H+分子是最早在星际云中观测到的离子之一，也是天体物理学中最重要的示踪剂之一。提高光谱精度可能使基本常数在空间或时间上的可能变化得到更好的约束。这项工作还将训练科罗拉多大学的一名学生学习量子逻辑光谱学所需的技术。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project is motivated by the opportunity to achieve coherent control of the quantum state of a single polyatomic molecule, and to exploit this control for precision measurements. This project will focus on trapping and controlling the molecular ion N_2H+, but the approach can be generalized to many other molecular ions. The N_2H+ molecular ion will be co-trapped and sympathetically cooled with a calcium ion to near the ground state of their shared motion. Pure quantum states of the molecular ion can then be initialized by projective measurements using quantum-logic spectroscopy, as recently demonstrated on the calcium hydride ion CaH+ by the investigators. This is important because this approach can advance quantum chemistry and may impact materials science and the chemical, biological, and pharmaceutical industries. In addition, new and superior reference spectra for astronomical observations could lead to a better understanding of interstellar gas clouds and the universe, including stringent tests of physics beyond the standard model. Ultimately, controlling molecules at the quantum level may enable precisely orchestrated collisions and fully controlled quantum chemistry.While laser cooling, trapping, and precision measurements of diatomic molecules are making tremendous progress, polyatomic molecules have eluded precision studies due to their complicated level structures and vast number of populated states. This project will extend the technique of quantum-logic spectroscopy to prepare pure quantum states of polyatomic molecules, and to manipulate and detect their states with minimal perturbations such as Doppler or pressure shifts. Precision spectroscopy will ultimately only be limited by the lifetime of the states and can therefore be pushed to levels that have only been reached previously in optical atomic clocks. The molecule N_2H+ was one of the first ions observed in interstellar clouds and remains one of the most important tracers in astrophysics. Improved spectroscopic precision might enable improved constraints on possible spatial or temporal variations of fundamental constants. This work will also train a student at the University of Colorado in techniques needed for quantum logic spectroscopy.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.