SGER: Response of Suspended Helium Films to Pulsed Atomic Helium Beams

这是SGER的一个项目，解决了超流氦物理中的一个基本问题。这些实验旨在测试这样的预测，即流体中的远程量子相干效应将导致一些非常快速的传输事件，与声音在超流体中传播的时间无关。氦原子的脉冲原子束撞击超流氦的悬浮膜。这些实验将测量氦原子通过薄膜传输的延迟时间。预测了两种不同延迟时间下的传输：较长的延迟时间与入射原子产生激发流体的声子-电子谱有关，随后原子从表面重新发射。第二个更短的延迟时间预计将出现在整个超流体与入射原子相互作用的瞬间虚拟位移，随后是再发射。这一事件的速度极快，可能在皮秒范围内。只会检测到较长的延迟(估计为微秒)传输。可以根据时间延迟信息和初始流量的知识来确定较短延迟传输的幅度。这一结果对于超流氦中类玻色凝聚态氦原子的相干特性具有重要意义。这些实验为学生提供了使用最先进的研究工具参与基础研究的令人兴奋的教育机会。%这是SGER的一个项目，解决了超流氦物理中的一个基本问题。该项目试图探测超流体的“相干”状态，在这种状态下，超流体中的所有氦原子作为一个单位做出反应。这一过程是将氦原子发射到悬浮的垂直氦薄膜中，并将其保持在绝对零度附近。一些入射的氦原子会迅速从超流氦的相干态反弹，一些会与氦原子相互作用并被延迟。这些实验试图测试对这两个事件的理论预测。这些结果对于包括原子气态玻色凝聚体在内的“玻色-爱因斯坦凝聚体”的一般场具有重要意义。这些实验为那些使用最先进的研究工具参与基础研究的学生提供了令人兴奋的教育机会。

9980329HalleyThis is an SGER project that addresses a fundamental issue in the physics of superfluid helium. The experiments are designed to test predictions that effects of long range quantum coherence in the fluid will lead to some very rapid transmission events, not associated with the time for sound propagation across the superfluid. Pulsed atomic beams of helium atoms impinge on a suspended film of superfluid helium. The experiments will measure delay times for helium atoms transmitted through the film. Transmission at two different delay times is predicted: the longer delay time is associate with production by the incident atoms of excitation of the phonon-roton spectrum of the fluid, followed by reemission of atoms from the surface. A second, shorter, delay time is predicted to arise from the momentary virtual displacement of the entire superfluid as a result of interaction with an incident atom, followed by reemission. This event is extremely fast, probably in the picosecond range. Only the longer delay (estimated at microseconds) transmission will be detected. The amplitude of the shorter delay transmission can be determined from the time delay information and knowledge of the initial flux. The results will be of fundamental interest in connection with the coherent character of the helium atoms in Bose-condensate-like state of superfluid helium. The experiments provide exciting educational opportunities for students to be involved in fundamental research using state-of-the-art research tools.%%%This is an SGER project that addresses a fundamental issue in the physics of superfluid helium. The project seeks to detect the 'coherent' state of superfluid in which all the helium atoms in the superfluid respond as a unit. The procedure will be to 'shoot' helium atoms off into a suspended vertical film of helium maintained near absolute zero. Some of the incident helium atoms will rapidly bounce off the coherent state of superfluid helium, some will interact with helium atoms and be delayed. The experiments seek to test theoretical predictions for these two events. The results are of fundamental importance for the general field of "Bose-Einstein condensates", which includes Bose condensates in the atomic gas state. The experiments provide exciting educational opportunities for students who are involved in fundamental research using state-of-the-art research tools.