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

普通观众摘要：该项目将开发基于镉的光学频率原子钟的实验技术，镉是下一代初级原子钟的有吸引力的候选者，并有望重新定义国际原子时间。原子钟实现了任何类型的最精确的测量。原子钟常规测量的微小滴答率差和短时间间隔具有广泛的应用，包括全球定位系统(GPS)、安全金融交易和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。原子钟解决了一些问题，如基本常量，如电子质量与质子质量之比，是否随时间变化。就在大爆炸之后，基本常量与现在不同了吗？镉原子对高精度时钟和其他精密测量的吸引力源于原子的适当激发对室温环境的热辐射不敏感，这对许多原子钟来说是一个限制。此外，一个实用的方面是，制造镉钟所需的激光预计比其他热敏性较小的时钟物种更可靠。镉也有一长串的八种同位素，在钟表使用的低温下，原子与原子的碰撞显著不同，绝对零度在百万分之一度以内。镉同位素包括多个玻色子和费米子，它们在超低温下有不同的行为。在这样的温度下，原子气体的量子力学性质变得显而易见，这些气体的基础科学在现代物理学研究中引起了广泛的兴趣。该项目还将为研究生提供多个现代技术领域的培训，包括激光、非线性光学、相干紫外光的产生、射频和微波技术、超高真空以及原子钟和频率控制。技术受众摘要：该研究计划的具体目标包括研究镉同位素的超冷散射特性，以及调查由于各种晶格构型的光学晶格光引起的频率漂移。晶格光频移与磁偶极跃迁和电四极跃迁的强度以及双光子跃迁引起的镉的小超极化率呈非线性关系。不同的晶格组态可以减少低晶格强度下晶格位置之间的隧道效应，导致较小的多普勒和晶格光移。不同的配置允许研究光移，以随后提高时钟的精度。该项目的另一个重要组成部分是与世界各地的原子钟组织合作，例如，评估对国际原子时(TAI)做出贡献的初级原子钟的精确度。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.