Laser Spectroscopy of Dense Positronium

稠密正电子的激光光谱

• 批准号: 1206100
• 负责人: Allen Mills
• 金额: $ 66万
• 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: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1206100&HistoricalAwards=false
• 关键词: Laser; Spectroscopy; Dense; Positronium

In this project Scientists at the University of California, Riverside (UCR) produce short bursts of millions of positronium atoms and cool them far below room temperature. The purpose is to prepare positronium ensembles suitable for making precision laser spectroscopy measurements and producing a Bose-Einstein condensed state. Positronium (chemical symbol Ps) is composed of an electron and a positron, the electron's antiparticle, bound together by the attraction of their opposite charges. Positronium is chemically like hydrogen but different because a positronium atom weighs only one-thousandth as much as a hydrogen atom and because the electron and positron in a positronium atom annihilate each other within about 100 nanoseconds. In previous work the UCR team has used dense bursts of positronium atoms at room temperature and above to measure Ps-Ps spin exchanging collision rates and to observe optical transitions between the ground and first excited states of Ps2 molecules. In the new work the team of UCR scientists and their students will use a new ps chirped pulse laser instrument developed under NSF MRI Award #1040590 to study the coherent excitation and deexcitation of Ps atoms in the adiabatic fast regime most familiar from NMR experiments. They will implement laser cooling of Ps in free space, using this technique to produce the rapid cooling needed for these short-lived atoms. In future experiments the methods developed in this project are expected to be used to produce and study the first Bose-Einstein condensate (BEC) formed from a dense gas of Ps atoms. The experiments of this project are of wide and compelling interest. Precision spectroscopy of purely electron-positron matter will give important information that can be compared with the essentially exact theory of quantum electrodynamics, which in turn will enable a unique search for new physics. The matter-antimatter BEC should exhibit fascinating quantum properties associated with collections of identical particles at comparatively high temperatures due to the light mass of the Ps atoms. The availability of cold Ps atoms emitted from a Ps BEC would be essential to possible measurements of the gravitational free-fall of Ps that would give us direct information about the nature of antimatter gravity for the first time. The possibility of a BEC producing stimulated electron-positron annihilation photons might someday be the basis for a gamma ray laser with important implications for defense and energy production. The project has a strong educational component since it will be partly carried out by graduate students who will receive high level training in a wide variety of leading edge techniques, in data analysis, and in the writing of scientific papers for high impact journals. The ongoing activities in the laboratory will form the basis for antimatter-based programs directed toward pre-college students and will be the centerpiece for laboratory tours and discussions for high school visitors and summer intern high school teachers.

在这个项目中，加州大学河滨分校(UCR)的科学家们产生了数百万个正电子原子的短时间爆发，并将它们冷却到远低于室温的温度。其目的是制备适合于进行精密激光光谱测量和产生玻色-爱因斯坦凝聚态的正电子系综。正电子(化学符号Ps)是由一个电子和一个正电子组成的，正电子是电子的反粒子，通过它们相反的电荷的吸引而结合在一起。正电子素在化学上类似于氢，但不同之处在于，正电子素原子的重量只有氢原子的千分之一，而且正电子素原子中的电子和正电子在大约100纳秒内相互湮灭。在之前的工作中，UCR团队使用了室温和更高温度下正电子原子的密集爆发来测量Ps-Ps自旋交换碰撞速率，并观察到PS2分子基态和第一激发态之间的光学跃迁。在这项新的工作中，UCR的科学家团队和他们的学生将使用一种由美国国家科学基金会核磁共振奖#1040590开发的新的ps啁啾脉冲激光仪器来研究在绝热快速区域中Ps原子的相干激发和去激发，这是核磁共振实验中最熟悉的。他们将在自由空间对Ps进行激光冷却，使用这项技术来产生这些短暂原子所需的快速冷却。在未来的实验中，该项目开发的方法有望用于生产和研究第一个由Ps原子组成的致密气体形成的玻色-爱因斯坦凝聚体(BEC)。这个项目的实验具有广泛而令人信服的兴趣。纯电子-正电子物质的精密光谱学将提供重要的信息，这些信息可以与量子电动力学的基本精确理论相比较，这反过来又将使对新物理的独特探索成为可能。由于Ps原子的轻质量，物质-反物质BEC应该会在相对较高的温度下显示出与相同粒子集合相关的迷人的量子性质。从Ps BEC发射的冷Ps原子的可用性对于可能测量Ps的重力自由落体是至关重要的，这将第一次给我们提供关于反物质引力性质的直接信息。BEC产生受激电子-正电子湮没光子的可能性有朝一日可能成为伽马激光的基础，对国防和能源生产具有重要意义。该项目具有很强的教育成分，因为它将部分由研究生实施，他们将接受各种前沿技术、数据分析和为影响较大的期刊撰写科学论文的高级培训。实验室中正在进行的活动将形成针对大学预科学生的基于反物质的项目的基础，并将成为高中访客和暑期实习生高中教师参观实验室和讨论的中心。