Precision Measurements with Nuclear Spins

在这个项目中，科学家们将寻找原子之间新的、非常弱的作用力。目前对物理学和宇宙学的理解允许这样一种可能性，即除了已知的四个基本力之外，由于新粒子的存在，还可能存在额外的弱力。为了寻找这种作用力，该研究小组将使用核磁共振医学扫描仪(核磁共振)基础技术的一种变体，对原子进行非常敏感的实验。在拟议的实验中，该小组将使用激光来定位原子的核自旋，并观察自旋方向如何随时间变化。他们预计，与早期的实验相比，灵敏度将提高几个数量级。除了允许科学家搜索原子之间的新作用力外，拟议中的实验还将在非常敏感的磁场测量和精确导航方面具有实际应用。提议描述了一个基于高灵敏度核自旋磁强计的精确测量计划。在该计划的一部分中，现有的碱金属稀有气体共磁力仪将被用来对几个假设的自旋相互作用设定新的限制。自旋和质量之间可能的相互作用可以由轴子或其他轻的伪标量粒子来调节。然而，现有的寻找这种效应的实验室实验还没有达到可以与天体物理极限竞争的灵敏度。其中一个拟议的实验将把这些极限提高3个数量级以上，并首次达到一个未知的参数空间范围。另一种可以由假想的轻粒子调节的相互作用是非磁性的自旋-自旋相互作用。利用现有的实验设备，最近对这种电子自旋相互作用的限制可以提高1到2个数量级。该计划的另一部分重点是开发一种新型的自旋共磁强计，使用两种稀有气体核自旋物种和带有Ramsey脉冲询问的碱金属读数。与现有方法相比，该方法具有更高的精度和更好的精度。新的协磁强计的灵敏度已经足以实现在普朗克尺度上寻找具有能量灵敏度的自旋-重力相互作用。在这项实验中，该小组的努力将集中在系统效应的控制上。

In this project scientists will search for new, very weak forces between atoms. The current understanding of physics and cosmology allows for the possibility that in addition to the four known fundamental forces there may be additional weak forces due to the existence of new particles. To search for such forces the group supported by the present grant will perform very sensitive experiments on atoms using a variant of the technique that underlies MRI medical scanners (nuclear magnetic resonance). In the proposed experiments the group will orient the nuclear spins of atoms using lasers and watch how the spin orientation changes with time. They expect to improve the sensitivity by several orders of magnitude compared with earlier experiments. In addition to allowing the scientists to search for new forces between atoms, the proposed experiments will also have practical applications for very sensitive measurements of magnetic fields and for precision navigation.The proposal describes a program of precision measurements based on high-sensitivity nuclear spin magnetometers. In one part of the program an existing alkali-metal noble-gas co-magnetometer will be used to set new limits on several hypothetical spin interactions. A possible interaction between spin and mass can be mediated by axions or other light pseudo-scalar particles. However, existing laboratory experiments searching for this effect have not yet reached a sensitivity that is competitive with astrophysical limits. One of the proposed experiments will improve these limits by more than 3 orders of magnitude and reach, for the first time, an unexplored range of parameter space. Another type of interaction that can be mediated by hypothetical light particles is a non-magnetic spin-spin interaction. Recent limits on such electron spin interactions can be improved by 1 or 2 orders of magnitude using already existing experimental apparatus. Another part of the program is focused on development of a new type of spin co-magnetometer, using two noble gas nuclear spin species and an alkali-metal readout with a Ramsey pulse interrogation. It is designed to have a higher accuracy as well as better precision compared with existing approaches. The sensitivity of the new co-magnetometer is already sufficient to realize a search for spin-gravity interaction with energy sensitivity at the Planck scale. The group's efforts will focus on the control of systematic effects in this experiment.