Spectroscopy of Dense Positronium

稠密正电子的光谱学

• 批准号: 1505903
• 负责人: Allen Mills
• 金额: $ 33.24万
• 依托单位: University of California-Riverside
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2022-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1505903&HistoricalAwards=false
• 关键词: Spectroscopy; Dense; Positronium

A Bose-Einstein condensate (BEC) is a cold gas of many identical atoms that have collected into the lowest energy state of a container. A BEC can exhibit frictionless flow and unique interference properties that make it an atomic analog of a laser. The coherence of light in lasers has found extraordinary applications in optical communication, medical imaging, and various industrial applications. The coherence of atoms may open new paths to atom-based quantum computation, simulation of new states of matter, and advances in high precision metrology. It has been proposed that a BEC formed from positronium (Ps) atoms (bound states of electrons and their positron antiparticles) would be of unique interest because it could exhibit double coherence, simultaneously condensing like a BEC and, at sufficiently high densities, exhibiting laser-like effects due to stimulated annihilation. Because positronium is thousands of times lighter than ordinary atoms, a positronium BEC does not need to be held at ultra-low temperatures and could even exist at room temperature, making it convenient for eventually making a practical gamma ray laser. An application of the positronium BEC would be the ability to induce coherent Ps atom emission to produce extremely monoenergetic atoms for ultrahigh precision optical spectroscopy measurements. The positronium BEC is predicted to form at 100 times higher density of positronium atoms than has ever been produced in a laboratory before. Two scientists from the University of California, Riverside (UCR) propose to study positronium at 100 times higher density and to observe the first positronium BEC. This is an ongoing project at the University of California Riverside (UCR) with the goal of studying the physics of a cold, dense gas of positronium (Ps), an ultra-light hydrogenic bound state of an electron and its positron antiparticle. Although the triplet ground state of Ps has a mean lifetime of only 142 ns, it is possible to make precision measurements of the energy levels of Ps and to observe Ps interactions with atoms, molecules and condensed mater. Scientists at UCR have thus far been able to create Ps densities sufficient to produce the dipositronium molecule (Ps2) for the first time. In this new phase of the project they will create a much denser Ps gas and study the effect that Bose-Einstein statistics is expected to have on atoms that are unit spin Bose particles. The specific objectives are: (1) Produce Ps pulses in a target with surface densities more than one hundred times greater than before; (2) Measure cooling rates of Ps atoms in cavities at cryogenic temperatures; (3) Observe an excess of low momentum cold Ps atoms in 2D cavities due to the effect of Bose statistics; and (4) Search for a Ps Bose-Einstein condensate (BEC) in 3D cavities at low temperature. Ps momentum distributions and temperatures for identifying a BEC will be measured directly in real time with a newly NSF-funded instrument specifically designed for this purpose.

玻色-爱因斯坦凝聚（BEC）是一种由许多相同原子组成的冷气体，这些原子聚集在一个容器的最低能量状态。 BEC可以表现出无摩擦流动和独特的干涉特性，使其成为激光的原子模拟物。 激光器中光的相干性在光通信、医学成像和各种工业应用中有着非凡的应用。原子的相干性可能为基于原子的量子计算、模拟新的物质状态以及高精度计量学的进步开辟新的途径。有人提出，由电子偶素（Ps）原子（电子及其正电子反粒子的束缚态）形成的BEC将是独特的兴趣，因为它可以表现出双相干性，同时像BEC一样凝聚，并且在足够高的密度下，由于受激湮灭而表现出类似激光的效应。由于正电子素比普通原子轻数千倍，因此正电子素BEC不需要保持在超低温下，甚至可以在室温下存在，这使得它便于最终制造实用的伽马射线激光器。 正电子偶素BEC的一个应用是诱导相干Ps原子发射产生极单能原子的能力，用于高精度光谱测量。正电子素BEC的正电子素原子密度预计将比以前在实验室中产生的高100倍。来自加州大学滨江分校（UCR）的两名科学家提议以100倍的密度研究正电子素，并观察第一个正电子素BEC。这是加州大学滨江（UCR）正在进行的一个项目，目标是研究电子偶素（Ps）的冷致密气体的物理学，电子及其正电子反粒子的超轻氢束缚态。虽然Ps的三重基态的平均寿命只有142 ns，但可以精确测量Ps的能级，并观察Ps与原子、分子和凝聚态物质的相互作用。到目前为止，UCR的科学家们已经能够创造出足以产生双电子素分子（Ps2）的Ps密度。在这个项目的新阶段，他们将创造一种密度更大的Ps气体，并研究玻色-爱因斯坦统计对单位自旋玻色粒子原子的影响。具体目标是：（1）在表面密度比以前大100倍以上的靶中产生Ps脉冲;（2）在低温下测量腔中Ps原子的冷却速率;（3）由于玻色统计的影响，在二维腔中观察到过量的低动量冷Ps原子;（4）在低温下在三维腔中寻找Ps玻色-爱因斯坦凝聚（BEC）。Ps的动量分布和温度，以确定一个BEC将直接测量真实的时间与一个新的NSF资助的仪器专门为此目的而设计的。