RUI: Classical and Quantum Ratchets in Josephson Arrays

RUI：约瑟夫森阵列中的经典和量子棘轮

• 批准号: 0804865
• 负责人: Kenneth Segall
• 金额: $ 17.5万
• 依托单位: Colgate University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-07-01 至 2012-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0804865&HistoricalAwards=false
• 关键词: RUI; Classical; Quantum; Ratchets; Josephson

*****NON-TECHNICAL ABSTRACT*****Noise and randomness in nature are not always undesirable. In recent years it has been learned that many physical systems have the capability to use noise and randomness to their advantage. Such a system is called a ratchet, indicating a system that only moves in one direction regardless of which direction it is pushed. An everyday example of a ratchet is a windmill, where regardless of which way the wind blows, net positive energy is produced. Ratchets can be realized in many different chemical, biological, optical and electronic systems. The open questions that exist relate to how much net motion is produced for different amounts and different types of noise. Scientists seek out different systems to try to quantify the answers to these questions. In this research, the ratchet effect is being studied in a superconducting circuit. Lithographic techniques, similar to ones used in the computer industry, can be used to fabricate tiny microscopic circuits made of superconducting metals. When these circuits are cooled to ultra-low temperatures, small bits of magnetic field called ?fluxons? can be trapped inside them. If the circuit layout has been designed correctly, these fluxons will be able to move in only one direction, thus exhibiting ratchet behavior. Studying the ratchet effect in a superconducting circuit is advantageous because many different circuit architectures can be engineered, each one operating slightly differently from the next. By measuring many such circuits, one can work toward more general ideas about how ratchets work. The broader impact of this research includes the training of undergraduate physics majors, who will be involved with much of the proposed studies. *****TECHNICAL ABSTRACT*****This individual investigator award supports an experimental study of the Ratchet Effect in arrays of superconducting Josephson junctions. The Ratchet Effect characterizes physical systems in which random noise and fluctuations can cause motion in a preferred direction. A physical system where the Ratchet Effect can be realized is an array of superconducting Josephson junctions, where applied electrical current can shuttle quanta of magnetic flux called fluxons. The motion of these fluxons can be ascertained by so-called switching current measurements, where the current-voltage characteristics are measured multiple times under the same conditions. Of particular interest are the different modes of transport for fluxons to ?depin? and move through the array. At low temperatures, the fluxon is expected to depin via quantum tunneling, although that has yet to be observed. At moderate temperatures the fluxon depins via thermal activation, characterized by Kramers? law type of behavior. At higher temperatures the fluxon can retrap again after being thermally activated, and move through in a series of depinning and retrapping events; this is known as fluxon diffusion. Our main objective is to observe these three domains and identify the ?crossover? regions in temperature. The broader impact of this work includes the training of undergraduate physics majors, who will perform much of the proposed research.

*****非技术抽象*****自然界中的噪音和随机性并不总是不受欢迎的。 近年来，据了解，许多物理系统都可以利用噪声和随机性来发挥其优势。 这样的系统称为棘轮，指示只能向一个方向移动的系统，无论其推动哪个方向。 棘轮的日常示例是风车，无论风向哪种方式吹来，都会产生净正能。 棘轮可以在许多不同的化学，生物学，光学和电子系统中实现。 存在的开放问题与不同量和不同类型的噪声产生了多少净运动有关。 科学家寻求不同的系统来试图量化这些问题的答案。 在这项研究中，正在在超导电路中研究棘轮效应。 与计算机行业中使用的类似的光刻技术可用于制造由超导金属制成的微型微观电路。 当将这些电路冷却至超低温度时，小磁场称为“磁通量”？可能被困在他们的内部。 如果正确设计了电路布局，则这些磁通量将只能向一个方向移动，从而表现出棘轮行为。 在超导电路中研究棘轮效应是有利的，因为可以设计许多不同的电路体系结构，每个电路架构与下一个电路的工作略有不同。 通过测量许多这样的电路，人们可以为棘轮的工作方式迈进更一般的想法。 这项研究的更广泛影响包括对本科物理专业的培训，他们将参与许多拟议的研究。 *****技术摘要*****该个别研究者奖支持了超导约瑟夫森连接阵列中棘轮效应的实验研究。 棘轮效应是物理系统的特征，其中随机噪声和波动会导致沿首选方向运动。 可以实现棘轮效应的物理系统是一系列超导的约瑟夫森连接，在该连接中，施加的电流可以乘坐称为磁通量的磁通量量子。 这些磁通量的运动可以通过所谓的开关电流测量值来确定，其中在相同条件下多次测量电流 - 电压特性。 特别感兴趣的磁通量是否不同的运输方式？并穿过阵列。 在低温下，尽管尚未观察到量子隧道，但磁通量预计将通过量子隧道挖掘。 在适度的温度下，Fluxon depins通过kramers特征的热激活？法律行为类型。 在较高的温度下，Fluxon可以在热激活后再次缩回，并在一系列繁殖和翻译事件中移动；这被称为Fluxon扩散。 我们的主要目标是观察这三个领域并确定跨界车？温度区域。 这项工作的更广泛影响包括对本科生专业的培训，他们将进行大部分建议的研究。