Research on Superfluid 3He Weak Links

超流体3He薄弱环节研究

• 批准号: 0244882
• 负责人: Richard Packard
• 金额: $ 72万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-10-15 至 2009-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0244882&HistoricalAwards=false
• 关键词: Research; Superfluid; 3He; Weak; Links

This project is focused on understanding the static and dynamic properties of weak link arrays (WLA) in superfluid 3He. The WLA consists of a quantum coherent array of apertures with diameter on the scale of the superfluid coherence length: typically a few tens of nanometers. Past research has already exposed several unanticipated features including: bi-stability, p-states, and new sources of superfluid dissipation. The past research was performed only at zero ambient pressure. The present project will explore the entire phase diagram of 3He, up to the melting pressure. The specific questions which will be answered include: What is the form of the current-phase relation, I(f), for all relevant temperatures and pressures? In the Josephson region, how does the critical current density scale? What is the limit, if any, to the number of apertures that will remain coherent in a weak link array? How do the dissipation processes change at elevated pressure? Are there always two stable states of the weak link array? Can a Josephson oscillation be driven by a temperature gradient as well as a pressure gradient? How does the I(f) function change in the transition from A to B phase? What is the nature of I(f)when there is an A-B bias across the array? Graduate students trained in the project will learn state-of-the-art techniques in microfabrication, ultra-cryogenics, SQUID magnetometry, electronic instrumentation and computer control and analysis."Macroscopic quantum" systems span the range from the interior of neutron stars to ultra-cold Bose-Einstein condensed gases. Relevant systems include superconductors, both conventional and high Tc, superfluid 4He and superfluid 3He, both A and B phases. It is a major goal of physics to understand why such diverse systems display phenomena which are generic to the entire class. This project will be directed toward understanding the physics of weak links in superfluid 3He. Weak links consist of devices which join two macroscopic quantum systems into a single, weakly connected whole. In the case of 3He the weak link is an array of nanometer-sized apertures, micro-machined in a 50nm thick "window". These devices have been shown to display a variety of unexpected phenomena, which have already led to a better understanding of superfluidity, high Tc superconductivity and quantum computing. Since past research has only covered experiments at zero ambient pressure, the present project will extend the range of exploration over a wide range of pressure and will include two different superfluid phases of 3He. To prepare them for future scientific careers, students participating in the project will receive state-of-the-art training in a variety of physics techniques including ultra-cryogenics, micro-machining, ultrasensitive magnetometry, electronics and computer control.

该项目的重点是了解超流3 He中弱连接阵列（WLA）的静态和动态特性。 WLA由孔径的量子相干阵列组成，孔径的直径在超流相干长度的尺度上：通常为几十纳米。 过去的研究已经揭示了一些意想不到的特征，包括：双稳态，p态和超流耗散的新来源。过去的研究仅在零环境压力下进行。 本项目将探索3 He的整个相图，直到熔化压力。 具体的问题，这将是回答包括：什么是形式的电流相位关系，I（f），所有相关的温度和压力？在约瑟夫森区域，临界电流密度如何缩放？ 在弱连接阵列中保持相干的孔径数目的限制是什么？ 压力升高时耗散过程如何变化？ 弱连接阵列是否总是存在两个稳定状态？ 约瑟夫森振荡能被温度梯度和压力梯度驱动吗？ 在从A相到B相的转变过程中，I（f）函数是如何变化的？ 当阵列上存在A-B偏置时，I（f）的性质是什么？ 在该项目中培训的研究生将学习最先进的技术，在微细加工，超低温，SQUID磁强计，电子仪器和计算机控制和分析。“宏观量子”系统涵盖了从中子星内部到超冷玻色-爱因斯坦凝聚气体的范围。 相关系统包括超导体，常规和高Tc，超流4 He和超流3 He，A相和B相。 物理学的一个主要目标是理解为什么如此不同的系统显示出对整个类都通用的现象。 该项目将致力于理解超流体3 He中弱连接的物理学。 弱连接是指将两个宏观量子系统连接成一个弱连接的整体的装置。 在3 He的情况下，薄弱环节是纳米尺寸的孔阵列，在50纳米厚的“窗口”中进行微加工。 这些器件已经显示出各种意想不到的现象，这些现象已经导致了对超流性，高Tc超导性和量子计算的更好理解。 由于过去的研究仅涵盖零环境压力下的实验，因此本项目将在广泛的压力范围内扩展勘探范围，并将包括两种不同的3 He超流体相。 为了使他们为未来的科学事业做好准备，参加该项目的学生将接受各种物理技术的最先进的培训，包括超低温，微加工，超灵敏磁力测量，电子和计算机控制。