Improving the Experimental Characterization of Dipole Matrix Elements in Rubidium

原子由束缚在原子核上的电子组成。这有时被描述为电子绕核运行，就像行星绕太阳运行一样，但实际上，原子尺度上的运动是由量子力学定律支配的。这些理论认为，即使电子是点状粒子，也不可能准确地说出电子在任何给定时间的位置。相反，电子的位置以概率的方式分布在原子核周围。为了了解原子的性质，有必要知道这种分布的性质。不幸的是，这种分布很难精确地直接观察到。通常，最好的方法是测量依赖于电子的原子属性，并使用这些值来约束分布。一组有用的性质是偶极矩阵元素，它有助于描述当原子被置于电场中时电子如何运动。即使偶极矩阵元素也不能直接测量，但它们可以从几种实验中可靠地推断出来。一种特别精确的方法叫做调谐波长光谱学。在这个项目中，调谐测量将用于获得铷原子的几个矩阵元素的改进值。为了举例说明为什么这些测量是重要的，考虑一下原子是否具有“手性”的问题，就像右手手套或左手手套一样。核物理学的理论和测量表明，原子核确实具有旋向性。这种旋向性在核物理学中的作用对于理解物质是如何在早期宇宙中产生的，以及为什么宇宙看起来是现在的样子非常重要。它可以在大型粒子加速器中进行研究，但这样做既困难又昂贵。在原子中，有少量的手性从原子核传递给电子。虽然影响很小，但原子的手性可以非常精确地测量，这对改进核物理理论很有用。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素。这个项目将提供的改进值将有助于实现这一目的，并以这种方式帮助提高我们对宇宙为什么是这个样子的理解。除了这些科学成果外，该项目还将为物理学本科生和研究生提供重要的训练机会。本项目使用的技术适用于量子计算、量子通信等其他重要研究领域，也适用于激光、量子传感等国家重要技术。该项目的参与者将做好充分准备，在这些领域作出贡献。在调谐波长光谱学中，原子被远离任何原子共振的激光束照射。在大多数情况下，这会导致原子的能量发生变化。能量可以增加或减少，这取决于光的波长。然而，在特定波长处，能量变化恰好为零。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。在这个项目中用来确定调谐波长的方法是原子干涉法。在这里，原子的整个波函数被分成两个分支，在空间上分开。一个分支穿过激光，任何产生的能量变化都会导致波函数的相移。当两个分支后来重新组合时，可以检测到这种相移。调谐波长是通过调节激光使相移为零来确定的。有多个波长会发生调谐，并且波长也取决于光的偏振。该项目将精确测量Rb原子在790nm波长附近的偏振依赖性，也将精确测量420 nm波长附近的偏振依赖性。通过结合这些测量，将有可能确定一些小而重要的术语，例如高海拔原子状态的总贡献，以及价电子和原子核心之间相互作用的影响。此外，光谱测量将用于测量从Rb的5P激发态到高能级的矩阵元素。虽然这不是一个高精度的测量，但结果将有助于解释实验，如上面描述的手性测量。最后，将探讨使用Rb原子进行手性（或宇称违反）测量的可能性。虽然Rb原子的这种效应比其他原子小，但Rb原子在现代冷却和俘获技术中使用起来非常方便。这些技术的好处可能是提高精度的一个有竞争力的选择，测量将能够直接利用将在项目中获得的改进的矩阵元素。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。

An atom consists of electrons bound to a nucleus. This is sometimes depicted with the electrons orbiting the nucleus like planets orbit the sun, but 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 a probabilistic way. In order to understand an atom’s properties, it is necessary to know the nature of this distribution. Unfortunately, the distribution is hard to observe directly with high precision. Typically, the best approach is to measure properties of the atom that depend on the electrons and use these values to constrain the distribution. One useful set of properties are the dipole matrix elements, which help describe how the electrons move when the atom is placed in an electric field. Even the dipole matrix elements cannot be measured directly, but they can be reliably inferred from several types of experiments. A particularly precise method is called tune-out wavelength spectroscopy. In this project, tune-out measurements will be used to obtain improved values for several matrix elements of the rubidium atom. To give one example of why these measurements are important, consider the question of whether an atom has “handedness,” like a right-handed or left-handed glove. Theories and measurements in nuclear physics indicate that the atomic nucleus does have 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 addition to these scientific results, the project will provide an important training opportunity for both undergraduate and graduate students in physics. The techniques used in this project are applicable to other important research areas such as quantum computing and quantum communication, as well as to nationally important technologies such as lasers and quantum sensing. Participants in this project will be well prepared to contribute in these areas.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. There are multiple wavelengths at which tuneouts occur, and the wavelengths also depend on the polarization of the light. This project will result in a precise measurement of the polarization dependence for Rb atoms at a wavelength near 790 nm, and also precise measurements near 420 nm. By combining these measurements, it will be possible to determine a number of small but important terms, such as the total contribution of the high-lying atomic states, and also the impact of interactions between the valence electron and the atomic core. In addition, spectroscopic measurements will be used to measure the matrix elements from the 5P excited state of Rb to high-lying states. Although this will not be a high-precision measurement, the results will be useful for interpreting experiments like the handedness measurement described above. Finally, the possibility of using Rb atoms for a handedness (or parity violation) measurement will be explored. Although the effect is smaller in Rb than in some other atoms, Rb atoms are very convenient to use with modern cooling and trapping techniques. It may be that the benefits of these techniques make a competitive option for improving precision, and the measurements would be able to take direct advantage of the improved matrix elements which will be obtained in the project.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.