Frequency metrology of the HD+ molecular ion: THz and vibrational spectroscopy at the 10-10 accuracy level

HD+分子非常重要，因为它是最简单的分子之一，只包含一个电子。对其振动跃迁频率的精确测量最终将允许(1)测试分子水平精确计算的理论方法；（ii）建立一个新的系统，以测量分子中的QED效应/测试QED理论；（iii）以一种新颖的方法确定电子与质子的质量比，并且可能比其他方法具有更高的精度；（iv）测量核性质，如四极矩，(v)测试核质量比的时间独立性。我们最近进行了反振动光谱分析，并以十亿分之2.3 （ppb）的相对精度测量了跃迁频率。我们的实验结果与之前获得的理论预测一致，并且可以确定α4阶的QED贡献，准确度约为10%。在本提案中，我们打算引入几个主要的实验改进，以达到接近2 / 1010 （0.2 ppb）的精度水平，这是十倍的改进。在这种精度水平上，实验结果将挑战改进的QED和超精细效应的理论公式和计算。我们的测量结果可能导致电子与质子质量比的另一种测定方法，其精度与目前建立的方法相似。除了在计量学中的应用之外，在拟议项目中开发的新方法引起了广泛的兴趣，因为它们将适用于各种其他分子离子。

The HD+ molecule is of fundamental importance because it is one of the simplest molecules, containing just a single electron. Precise measurement of its vibrational transition frequencies will ultimately allow (i) to test theoretical methods of precision calculation of molecular levels; (ii) establish a new System allowing to measure QED effects / test QED theory in molecules; (iii) to determine the ratio of electron-to-proton mass in a novel way and with potentially higher precision than with alternative methods; (iv) to measure nuclear properties such as quadrupole moments, (v) to test the time-independence of nuclear mass ratios.We have recently performed ro-vibrational spectroscopy and measured the transition frequency with a relative accuracy of 2.3 parts per billion (ppb). Our experimental result is in agreement with theoretical predicitions that were obtained shortly before and allowed the determination of QED contributions of order α4 to about 10% accuracy.In this proposal, we intend to introduce several major experimental improvements in order to reach an accuracy close to the level of 2 parts in 1010 (0.2 ppb), a tenfold improvement. At this level of accuracy, the experimental results will challenge an improved theoretical formulation and calculation of the QED and hyperfine effects. Our measurements could lead to an alternative determination of the electron-to-proton mass ratio, with an accuracy similar to that of currently established approaches.Apart from this application in metrology, the new methods to be developed in the proposed project are of wide interest since they will be applicable to a large variety of other molecular ions.