Precision Measurements with Laser-Cooled Cadmium: Optical-Lattice Clock and Cold Collision Experiments

摘要：该项目将开发基于镉的光频原子钟的实验技术，镉是下一代主原子钟的有吸引力的候选者，并有望重新定义国际原子时。原子钟能实现所有类型中最精确的测量。原子钟通常测量的微小的滴答率差异和较短的时间间隔具有广泛的应用，包括全球定位系统（GPS）、安全的金融交易以及美国和国际官方时间。原子钟的科学应用包括广义相对论和基础物理学的测试、大地测量学、长基线干涉测量学和计量学。原子钟解决的问题包括一些基本常数，比如电子质量与质子质量之比，是否随时间变化。大爆炸之后，基本常数是否与现在不同？镉原子对高精度时钟和其他精密测量的吸引力源于镉原子对室温环境的热辐射的适当激发不敏感，这是许多原子钟的限制。此外，一个实际的方面是，制造镉原子钟所需的激光预计比其他具有小热敏度的原子钟更可靠。镉也有一长串的八种同位素，它们在时钟使用的低温下（绝对零度的百万分之一），原子间的碰撞有显著不同。镉同位素包括多个玻色子和费米子，它们在超冷温度下具有不同的行为。在这样的温度下，原子气体的量子力学性质变得明显，这些气体的基础科学在现代物理学研究中具有广泛的兴趣。该项目还将为研究生提供现代技术许多领域的培训，包括激光、非线性光学、相干紫外光的产生、射频和微波技术、超高真空、原子钟和频率控制。技术听众摘要：本研究项目的具体目标包括研究镉同位素的超冷散射特性和研究不同晶格结构下光学晶格光的频移。晶格光频移非线性地依赖于由磁偶极子和电四极子跃迁引起的强度，以及双光子跃迁引起的镉的小超极化。不同的晶格结构可以减少低晶格强度下晶格位置之间的隧穿，导致更小的多普勒和光移。不同的结构可以研究光移，从而提高时钟的精度。该项目的另一个重要组成部分是与世界各地的原子钟小组合作，例如，评估构成国际原子时（TAI）的主原子钟的准确性。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。

General audience abstract:The project will develop experimental techniques for optical-frequency atomic clocks based on Cadmium, an attractive candidate for the next generation of primary atomic clocks and an anticipated redefinition of international atomic time. Atomic clocks realize the most accurate measurements of any type. The small tick-rate differences and the short time intervals that atomic clocks routinely measure have wide-ranging applications, including the Global Positioning System (GPS), secure financial transactions, and official U.S. and international time. Scientific applications of atomic clocks include tests of general relativity and fundamental physics, geodesy, long baseline interferometry, and metrology. Atomic clocks address questions such as whether fundamental constants, for example the ratio of the mass of an electron and the mass of a proton, change in time. Just after the big bang, were fundamental constants different than they are now? The attractiveness of Cadmium atoms for highly accurate clocks and other precision measurements stems from an insensitivity of a suitable excitation of the atoms to thermal radiation from room-temperature surroundings, a limitation for many atomic clocks. Additionally, a practical aspect is that the lasers needed to make a Cadmium clock are expected to be more reliable than for other clock species with small thermal sensitivities. Cadmium also has a long series of eight isotopes, which have significantly different atom-atom collisions at the low temperatures used in clocks, within a millionth of a degree of absolute zero. The Cadmium isotopes include multiple bosons and fermions, which have different behaviors at ultra-cold temperatures. At such temperatures, the quantum-mechanical nature of atomic gases becomes evident and the basic science of these gases is of broad interest in modern physics research. The project will also provide training of graduate students in many areas of modern technology, including lasers, non-linear optics, the generation of coherent ultraviolet light, radio-frequency and microwave techniques, ultra-high vacuum, and atomic clocks and frequency control.Technical audience abstract:Specific goals for this research program include studying the ultracold scattering properties of the cadmium isotopes and investigating the frequency shifts due to the optical lattice light in a variety of lattice configurations. The lattice light frequency shifts depend non-linearly on the intensity due to magnetic dipole and electric quadrupole transitions, and the small hyperpolarizability of cadmium from two-photon transitions. Different lattice configurations can reduce tunneling between lattice sites at low lattice intensities, leading to smaller Doppler and lattice light shifts. The different configurations allow the light shifts to be studied to subsequently improve the accuracy of clocks. Another important component of the project is collaborations with atomic clock groups around the world, for example, to evaluate the accuracies of primary atomic clocks that contribute to International Atomic Time (TAI).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.