Production of Positronium atoms, ions, and molecules

正电子是一种由电子-正电子对组成的原子系统，在其原子性质方面与氢有许多相似之处。然而，由粒子-反粒子对组成的Ps系统比氢更复杂，因为自湮灭和虚湮灭过程的可能性在基本能级结构和实验的实用性中起着很大的作用。然而，正电子捕获技术的最新进展已经使生产高密度Ps气体成为可能，其中Ps-Ps散射很容易被观察到，并且可以用激光探测。实验成功地产生了Ps2分子，并用激光激发它们，观察了Ps-Ps散射，以及随后Ps气体的自旋极化。此外，还观察到与介观多孔膜内表面相互作用引起的Ps能级的变化。随着光束密度的增加，将有可能以更高的效率产生Ps2分子，因此可以更详细地研究它们的性质。一个更强大的Ps2分子源也允许正负Ps离子的产生，这可以用激光来分解Ps2分子。这些离子和分子是稳定的原子系统（尽管它们会自我湮灭），可以用光学方法进行研究。因为它们是由三个或四个质量近似相等的物体组成的，就像玻恩-奥本海默方法（电子和原子核被独立处理）一样，不能使用。因此，Ps离子和分子对理论家提出了一个有趣的挑战。它们还具有迄今尚未在实验中广泛研究的独特性质。冷Ps原子源的可用性也是几个实验努力的关键一步，包括高分辨率光谱和（反）物质波干涉测量，可以用来测试束缚态QED理论和寻找新的物理。Ps原子是纯QED系统，因为QED是光和轻子的理论，所以它们对非QED效应特别敏感，比如未知的粒子或力。如果能对这些最简单的系统进行足够详细的研究，它们可能会揭示宇宙中一些保守得最好的秘密。

Positronium is an atomic system made from an electron-positron pair, which has many similarities to hydrogen in terms of its atomic properties. Being composed of a particle-antiparticle pair makes the Ps system more complex than hydrogen, however, because the possibility of both self and virtual annihilation processes plays a large role in the fundamental energy level structure and in the practicalities of performing experiments. Nevertheless, recent advances in positron trapping technology have made it possible to produce high-density Ps gases in which Ps-Ps scattering is readily observed, and which can be probed with lasers. Experiments have succeeded in producing Ps2 molecules and exciting them with laser light, observing Ps-Ps scattering, and the subsequent spin polarization of a Ps gas. The shift of Ps energy levels caused by interactions with the internal surfaces of mesoscopic porous films has also been observed.With an increased beam density it will be possible to generate Ps2 molecules with higher efficiency, and therefore to study their properties in much greater detail. A more robust source of Ps2 molecules also allows for the production of both positive and negative Ps ions, which can be created using lasers to break up a Ps2 molecule. These ions and molecules are stable atomic systems (although they do self-annihilate) and can be studied optically. Because they are composed of three or four bodies of equal mass approximations like the Born-Oppenheimer approach (where electrons and nuclei are treated independently) cannot be used. Thus, Ps ions and molecules present an interesting challenge to theorists. They also possess unique properties that have so far not been widely studied experimentally. The availability of a source of cold Ps atoms is also a key step in several experimental endeavors, including high resolution spectroscopy and (anti)matter wave interferometry, which can be used to test bound state QED theory and search for new physics. Ps atoms are pure QED systems, as QED is a theory of light and leptons, and so they are especially sensitive to non-QED effects, such as unknown particles or forces. If they can be studied in sufficient detail these simplest of systems may reveal some of the best kept secrets in the universe.