Quantum phenomena in condensed atomic and molecular hydrogen

非技术描述：氢原子中的自旋电子表现为微小的磁铁，当嵌入固体氢分子中时，它们可以相互作用，导致磁相的形成。根据量子力学，氢原子可以隧穿分子氢的晶格。在足够低的温度和足够高的密度下，嵌在氢分子晶格中的氢原子会有量子重叠，这可能导致一种叫做玻色-爱因斯坦凝聚的现象，在这种现象中，单个原子失去了它们的身份，整个系统的行为就像一个单一的量子波。这导致了超流体特性，如无摩擦流动。本研究的目标是在最低温度下研究固体氢分子中的氢原子，以寻找嵌入固体氢分子中的氢原子的玻色-爱因斯坦凝聚和随后的超流体行为。如果成功，该项目将开创凝聚态物理的一个新领域，并使研究化学反应的化学家受益。第二个目标是观察分子对氢团簇集合中的超流动性，作为玻色-爱因斯坦凝聚的另一个证明。研究生在获得远低于1 K温度的技术方面接受了广泛的培训。在德克萨斯A&amp；M大学物理节期间，将进行积极的推广活动，包括讲座、与高中教师会面和示范。项目还与芬兰低温集团保持国际合作。技术描述：本研究项目的基本目标是观察嵌入在固体分子氢膜中的氢原子系统中的新量子现象。这些氢原子即使在低于1K的温度下仍保持离域，如果冷却到足够低的温度，可能会表现出玻色-爱因斯坦凝聚和超固体。这项工作包括将稀释冰箱与波莫兰丘克冷却阶段相结合，将固体氢分子中的氢原子样品冷却到1 mK，在那里有望出现新的量子现象。利用128 GHz电子自旋共振技术可以探测氢原子的基态居群和玻色-爱因斯坦凝聚的可能发生。最近在T=0.1-0.8 K时固体分子氢膜中氢原子的核极化相的发现暗示了可能的量子跃迁。将实验扩展到更低的温度应该有助于阐明这些相的起源以及它们与氢原子玻色-爱因斯坦凝聚的可能关系。此外，氢原子在固体氢分子中的空间量子扩散研究也在进行中，该研究可以确定氢原子的有效质量和估计玻色-爱因斯坦凝聚的起始温度。该项目的第二个目标是在含有大量小的对氢团簇的宏观样品中寻找氢超流动性。在0.15 K的温度下，实验观察了包裹在氦纳米液滴中的单个小对氢团簇的超流动性。在石英微天平表面生长的多孔固体霓虹灯薄膜中嵌入了一组小的对氢簇，研究了对氢分子的超流动性。对氢团簇中超流动性的开始被记录为通过转变温度时微平衡频率的变化。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。

Non-technical description: Spinning electrons in hydrogen atoms behave as tiny magnets which can interact when embedded in solid molecular hydrogen leading to formation of magnetic phases. Hydrogen atoms can tunnel through the lattice of molecular hydrogen according to quantum mechanics. At low enough temperatures and high enough densities, the hydrogen atoms embedded in the lattice of molecular hydrogen have quantum overlap which can lead to a phenomenon called Bose-Einstein condensation, in which individual atoms lose their identities and the whole system behaves like a single quantum wave. This leads to superfluid properties such as flow without friction. A goal of this research is to study hydrogen atoms in solid molecular hydrogen at the lowest temperatures to look for Bose-Einstein condensation and subsequent superfluid behavior of hydrogen atoms embedded in solid molecular hydrogen. If successful, this project could initiate a new field in condensed matter physics and benefit chemists studying chemical reactions. A second goal is the observation of superfluidity in the collection of molecular para-hydrogen clusters as another demonstration of Bose-Einstein condensation. Graduate students get extensive training in techniques used to attain temperatures well below 1 K. Active outreach programs including lectures, meetings with high school teachers and demonstrations are performed during the Texas A&M University Physics Festival. The project also maintains the international collaboration with the low temperature group in Finland.Technical description: This research project pursues the fundamental goal of observing new quantum phenomena in a system of hydrogen atoms embedded in solid molecular hydrogen films. These hydrogen atoms remain delocalized even at temperatures below 1K and may exhibit Bose-Einstein condensation and supersolidity if cooled to low enough temperatures. This work involves a dilution refrigerator combined with a Pomeranchuk cooling stage to cool the samples of hydrogen atoms in solid molecular hydrogen down to 1 mK, where new quantum phenomena is expected to occur. The hydrogen atom ground state population and possible onset of Bose-Einstein condensation can be probed by using 128 GHz electron spin resonance techniques. The recent discovery of the nuclear polarized phases of hydrogen atoms in solid molecular hydrogen films at T=0.1-0.8 K implies possible quantum transitions. Extending the experiments to lower temperatures should help throw light on the origin of these phases and their possible relation to hydrogen atom Bose-Einstein condensation. Additionally, studies are in progress of hydrogen atom spatial quantum diffusion in solid molecular hydrogen which allows determination of hydrogen atom effective mass and estimation of the onset temperature for Bose-Einstein condensation. The second goal of the project is the search for hydrogen superfluidity in macroscopic samples containing a large number of small para-hydrogen clusters. Superfluidity of single small para-hydrogen clusters encapsulated in helium nanodroplets was observed experimentally at 0.15 K. The search for superfluidity of para-hydrogen molecules is performed for a collection of small para-hydrogen clusters embedded in porous solid neon films grown on the surface of a quartz microbalance. The onset of superfluidity in para-hydrogen clusters is registered as a microbalance frequency change while passing through the transition temperature.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.