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Precision Measurement of Atomic Dipole Matrix Elements Using Tune-Out Wavelength Spectroscopy

使用调谐波长光谱精确测量原子偶极子矩阵元素

基本信息

批准号：
1607571
负责人：
Charles Sackett
金额：
$ 59.24万
依托单位：
University of Virginia Main Campus
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2016
资助国家：
美国
起止时间：
2016-09-01 至 2020-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1607571&HistoricalAwards=false
关键词：
Precision Measurement Atomic Dipole Matrix

项目摘要

Although an atom is sometimes depicted with the electrons orbiting the nucleus like planets orbit the sun, in reality motion at the atomic scale is governed by the laws of quantum mechanics. These say that even though the electron is a point-like particle, it is impossible to say exactly where an electron is at any given time. Instead, the location of an electron is spread out around the nucleus. In order to understand an atom's properties it is necessary to know how all its electrons are spread out. One useful set of properties that measure how electrons are distributed are the "dipole matrix elements" (numerical values that arise from particular mathematical constructs which help describe how the electron distributions change when the energy of the atom is changed). Even the dipole matrix elements cannot be measured directly, but they can be reliably inferred from several types of experiments. Recently, a new way to obtain dipole matrix elements more precisely has been demonstrated, called tune-out wavelength spectroscopy. For this project, tune-out wavelength measurements will be used to obtain improved values for several matrix elements of the rubidium atom. One example of why these measurements are important relates to whether an atom has "handedness," like a right-handed or left-handed glove. Theories and measurements in nuclear physics indicate that the atomic nucleus has a handedness. The role of this handedness in nuclear physics is very important for understanding how matter was created in the early universe, and why the universe looks the way it does now. It can be studied in large particle accelerators, but doing so is difficult and expensive. In an atom, a slight amount of the handedness is transmitted from the nucleus to the electrons. Although the effect is small, the atomic handedness can be measured very precisely and this has been useful for improving nuclear physics theories. However, relating the atomic measurement to nuclear physics requires accurate dipole matrix elements. The improved values that will be provided by this project will be useful for this purpose, and in this way help improve our understanding of why the universe is as it is.In tune-out wavelength spectroscopy, the atom is illuminated by a laser beam that is tuned far from any atomic resonances. In most cases, this causes the energy of the atom to change. The energy can either increase or decrease, depending on the wavelength of the light. At specific wavelengths, however, the energy change is exactly zero. The value of these wavelengths depends on the dipole matrix elements of the atom, and by measuring the wavelength accurately the ratios of various matrix elements can be determined with high precision. The method used in this project to determine the tune-out wavelength is atom interferometry. Here the overall wave function of the atom is split into two branches that separate in space. One branch passes through the laser, and any resulting energy change results in a phase shift of the wave function. When the two branches are later recombined, this phase shift can be detected. The tune-out wavelength is determined by adjusting the laser to make the phase shift zero. A particular focus of this project will be to observe how the tune-out wavelength depends on the polarization of the laser light. By combining polarization-dependent measurements at a few different tune-out wavelengths, it is possible to accurately extract several groups of small matrix elements that are otherwise very challenging to measure or calculate. These small matrix elements are nonetheless important, as they represent dominant uncertainties in measurements of atomic parity violation and other atomic properties like the dc electric polarizability.

尽管原子有时被描绘成电子围绕原子核运行，就像行星绕太阳运行一样，但实际上原子尺度上的运动是受量子力学定律支配的。他们说，即使电子是点状粒子，也不可能说出电子在任何给定时间的确切位置。相反，电子的位置分布在原子核周围。为了了解一个原子的性质，有必要知道它所有的电子是如何扩散的。衡量电子如何分布的一组有用的属性是“偶极矩阵元”(从特定的数学结构中产生的数值，这些数值有助于描述当原子的能量改变时电子分布如何变化)。即使是偶极矩阵元也不能直接测量，但可以从几种类型的实验中可靠地推断出来。最近，一种更精确地获得偶极矩阵元的新方法被证明，称为调谐波长光谱学。在这个项目中，调谐波长测量将被用来获得Rb原子的几个矩阵元素的改进值。为什么这些测量很重要的一个例子是关于一个原子是否有“惯用手”，比如右手手套或左手手套。核物理中的理论和测量表明，原子核具有利手。这种左撇子在核物理中的作用对于理解早期宇宙中物质是如何产生的，以及为什么宇宙看起来像现在这样是非常重要的。它可以在大粒子加速器中进行研究，但这样做既困难又昂贵。在原子中，极少量的左手原子从原子核传递到电子。虽然影响很小，但可以非常精确地测量原子的利手性，这对改进核物理理论是有用的。然而，将原子测量与核物理联系起来需要精确的偶极矩阵元。这个项目将提供的改进的值将对这个目的有用，通过这种方式帮助我们更好地理解为什么宇宙是这样的。在调谐波长光谱学中，原子被一束远离任何原子共振的激光照射。在大多数情况下，这会导致原子的能量发生变化。能量可以增加，也可以减少，这取决于光的波长。然而，在特定的波长，能量变化完全为零。这些波长的值取决于原子的偶极矩阵元素，通过精确测量波长，可以高精度地确定各种矩阵元素的比例。本项目中用来确定调谐波长的方法是原子干涉法。在这里，原子的整体波函数被分成两个在空间上分开的分支。一个分支穿过激光器，任何由此产生的能量变化都会导致波函数的相移。当两个分支稍后重新组合时，可以检测到这种相移。调谐波长是通过调节激光器使相移为零来确定的。这个项目的一个特别的重点将是观察调谐波长如何依赖于激光的偏振。通过组合几个不同调谐波长的偏振相关测量，可以准确地提取几组小矩阵元素，否则测量或计算起来非常困难。尽管如此，这些小的矩阵元素仍然很重要，因为它们代表了原子宇称破坏和其他原子属性(如直流电极化率)测量的主要不确定性。