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: 0509450
• 负责人: Kenneth Segall
• 金额: --
• 依托单位: Colgate University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-06-15 至 2008-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0509450&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. This Research at an Undergraduate Institution (RUI) award supports studies of the ratchet effect in a superconducting circuit. Lithographic techniques, similar to the 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 only be able to move in 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 different than 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 Research at an Undergraduate Institution (RUI) 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 measuring voltages in the array. A series of low temperature measurements will be performed on previously fabricated Josephson arrays which have been designed to display the Ratchet Effect. Of particular interest is how different types of fluctuations in the arrays cause different types of ratchet behavior. Classical thermal fluctuations, always present in varying degrees, cause the so-called rocking ratchet effect. At low enough temperatures and dissipation, quantum fluctuations can cause additional transport; this is known as the quantum ratchet effect. Finally, types of 1/f fluctuations often present in Josephson junctions manifest themselves in yet another way, in a kind of ratchet known as a flashing ratchet. Many of these effects have not yet been observed, and this research aims to shed more light on these issues. 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。 本科机构（RUI）奖的这项研究支持了超导电路中棘轮效应的研究。 具有类似于计算机行业的光刻技术，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，可能会将称为“磁通子”的小磁场捕获。 如果正确设计了电路布局，这些磁通量只能朝一个方向移动，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****本科机构奖（RUI）奖的这项研究支持对棘轮阵列中的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测量阵列中的电压来确定。 将对先前制造的约瑟夫森阵列进行一系列低温测量值，这些阵列旨在显示棘轮效应。 特别有趣的是，阵列中不同类型的波动如何引起不同类型的棘轮行为。 经典的热波动始终以不同的程度存在，会导致所谓的摇摆棘轮效应。 在足够低的温度和耗散时，量子波动会导致额外的运输。这被称为量子棘轮效应。 最后，约瑟夫森连接中经常出现的1/f波动的类型以另一种方式表现出来，这种棘轮被称为闪烁的棘轮。 尚未观察到其中许多效果，这项研究旨在更多地阐明这些问题。 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。