Precision Measurements of Quantum Scattering Phase Shifts with a Juggling Fountain Clock

本实验研究计划将在原子钟内精确测量超冷铯原子的量子散射相移。该小组用一种新型的散射实验证明了这些测量结果，该实验将铯原子在超冷温度下以两个原子钟状态的相干叠加态散射出去。每个时钟状态都经历了s波散射相移，通过仅检测每个原子波函数的散射部分，可以直接观察到散射相移的差异，即拉姆齐条纹的相移。一个独特的特点是观测到的散射相移的差异与原子密度无关，为散射测量提供了原子钟精度。在高精度的情况下，该小组已经观察到两个能量在10到50微开尔文之间碰撞的云的许多费希巴赫共振，最近在一个云内的碰撞能量为1微开尔文。他们将进行首次精确演示，这有望显著提高Cs-Cs相互作用的知识。散射长度目前对铯原子钟的精度和操作参数的影响还不够了解，特别是计划在国际空间站上飞行的空间原子钟（ACES）时钟。该小组将评估主要由背景引起的系统误差，并提高相位测量的精度。改进的理论理解可以指导未来的测量，潜在地研究不同的角动量，相对于能量和磁场，以及各种内部状态。该小组还将与世界各地的国家实验室合作，以提高最好的原子钟的准确性。该小组在主原子钟微波腔的设计方面提供了独特的专业知识，并参与了主原子钟的精度评估。作为杂耍实验工作的一部分而发展起来的想法为光学晶格钟的超冷费米子相互作用提供了解释，最近在芯片级原子钟和Li-6费米子的射频跃迁中实验观察到。准确的计时对于导航、通信、全球定位和国家安全至关重要。这个小组最近的研究大大提高了构成国际原子时（TAI）的原子钟的准确性。他们的贡献对于实现目前最精确的原子钟至关重要。这项研究的新进展减少了以前限制原子钟性能的许多大的系统误差。早期的工作导致铷被采纳为国际单位制（SI）秒定义的第一个修正案，新的空间时钟设计，以及对精密测量中超冷碰撞引起的频率偏移的理解。该研究将进一步推动最精确的精密测量和对超冷原子-原子相互作用的理解。对研究生和本科生进行激光、电光、射频和微波技术、原子钟和频率控制等许多现代技术领域的培训，对国家科学队伍的发展非常重要。

This experimental research program will make precision measurements of quantum scattering phase shifts of ultracold cesium (Cs) atoms in an atomic clock. The group has demonstrated these measurements with a new type of scattering experiment that scatters a cesium atom in a coherent superposition of its two clock states off atoms in a pure state at ultracold temperatures. Each clock state experiences an s-wave scattering phase shift and, by detecting only the scattered part of each atom's wavefunction, the difference of the scattering phase shifts is directly observed as a phase shift of Ramsey fringes. A unique feature is that the observed difference of the scattering phase shifts is independent of the atomic density, providing atomic clock accuracy to scattering measurements. With high precision, the group has observed a number of Feshbach resonances with two clouds colliding at energies between 10 and 50 microKelvin, and recently at collision energies of order 1 microKelvin, within a single cloud. They will perform a first accuracy demonstration, which is expected to significantly improve the knowledge of the Cs-Cs interactions. The scattering lengths are presently insufficiently known that they impact the accuracy and operational parameters of cesium clocks, particularly the Atomic Clock Ensemble in Space (ACES) clock scheduled to fly on the International Space Station. The group will evaluate systematic errors, principally due to backgrounds, and improve the precision of the phase measurements. An improved theoretical understanding can guide future measurements, potentially studying different angular momenta, versus energy and magnetic field, and for various internal states. The group will also collaborate with national labs around the world to improve the accuracy of the best atomic clocks. The group provides a unique expertise on the design of microwave cavities for primary atomic clocks and participates in the accuracy evaluation of primary atomic clocks. Ideas developed as part of the juggling experimental work provided the explanation of the interactions of ultracold fermions for optical lattice clocks, recently experimentally observed in a chip-scale atomic clock and with a radio frequency transition in Li-6 fermions. Accurate time keeping is crucial for navigation, communication, global positioning, and national security. Recent research of this group has significantly advanced the accuracy of the atomic clocks that contribute to International Atomic Time (TAI). Their contributions were essential to realize the currently most accurate atomic clock. Novel advancements by the research have reduced many large systematic errors that previously limited the performance of atomic clocks. Earlier work had led to rubidium being adopted as the first amendment to the definition of the International System of Units (SI) second, novel space clock designs, and an understanding of the frequency shifts due to ultracold collisions in precision measurements. The research will further advance the most accurate precision measurements and the understanding of ultracold atom-atom interactions. The training of graduate and undergraudate students in many areas of modern technology from lasers, electro-optics, radio-frequency and microwave techniques, and atomic clocks and frequency control, is important for the development of the nation's scientific workforce.