Confinement of gaseous atoms with superfluid helium film and its application to the test of time-reversal symmetry

本项目的目的是实现液氦温度下的碱蒸气池，通过在池壁镀上超流氦膜，适用于与自旋相关的基础物理，特别是用于测量原子电偶极矩（EDM），检验时间反演对称性。通过本课题的研究，我们可以得到如下重要成果。(1)实验上可实现气态碱原子寿命达10-100 s的碱蒸气电池。(2)我们可以发展一种新的产生碱金属气态原子的方法，即“光诱导原子解吸LIAD”方法，它可以在弱连续光下产生气态原子，而没有强对流。(3)结果表明，壁面液氦的超流性对LIAD起着重要的作用，并揭示了其机理。(4)对冷池中产生的原子进行了光抽运实验。我们发现自旋弛豫时间由原子寿命10-100 s决定。(5)我们发展了利用法拉第效应测量原子自旋的方法，使对自旋态的扰动最小化。本文还提出了自旋非破坏测量方法，该方法非常适合于原子电火花测量。(7)我们还提出并研究了一种新的观测自旋极化分布的方法--光学磁共振成像。(8)作为冷氦气对碱金属原子的一种新的作用，我们发现氦原子与激发态碱金属原子结合形成激基缔合物和激基复合物。通过对这些激发态分子的光谱研究，我们可以确定它们的能量，包括振动能，从而得到它们的形成信息。

The purpose of this project is to realize the alkali vapor cell at liquid helium temperature, by coating the cell walls with superfluid helium film, suitable for the spin- related fundamental physics, particularly to the measurement of atomic electric dipole moment (EDM) for the test of time reversal symmetry. Through this project we could get various important results as follows.(1) We could realize experimentally alkali vapor cell, where the life of gaseous alkali atoms was as long as 10-100 s.(2) We could develop a novel method of production of alkali gaseous atoms, so called "light-induced atom desorption LIAD" method, witch can produce gaseous atoms with weak cw light, without strong convection.(3) It was found that the superfluidity of the liquid helium on the wall plays an important role for the LIAD, and the mechanism could be revealed.(4) Optical pumping experiment was made to the produced atoms in the cold cell. We found that the spin-relaxation time was determined by the lifetime of atoms 10-100 s.(5) We developed the method of atomic spin with the Faraday effect, which minimized the perturbation to the spin state. We also proposed the method of spin non-demolition measurement, which is very suitable for the atomic EDM measurement.(7) We also proposed and studied a novel method to observe the special distribution of spin polarization, optical magnetic-resonance imaging.(8) As a new effect of cold helium gas to alkali-metal atom, we found the formation of excimer and exciplexes, where helium atoms are sticking to the excited state alkali atoms. Trough spectroscopic studies of these excited-state molecules, we could determine their energies, including vibrational energies, and could get the information of formation.