Manipulation of Hole-pinned Vortices: Classical and Quantum

非技术摘要超导体可以无损耗地传输电流，也会排出磁场。然而，在某些临界场以上，磁通量通过形成一系列被称为涡旋的超导电子涡流进入超导体。这些涡旋的运动会破坏超导特性。高场磁铁避免了这个问题，因为微观缺陷钉住了涡旋。这个研究小组的方法不是让涡旋随机地被缺陷钉住，而是通过在它们附着的薄膜中创建纳米孔的图案，以受控的方式钉住它们。通过引入外部电场和磁场，应该能够以受控的方式在钉扎点之间移动涡旋。这样的操作可能被用于存储数据、执行计算或两者兼而有之，所有这些都在同一组孔中。由于涡流本质上是稳定的，只有在胶片边缘或遇到反涡流时才会被破坏，所以它们携带的“信息比特”是安全的。此外，它们可以具有亚微米尺寸，并可能在亚纳秒时间尺度上做出响应，潜在地促进了高速、高密度的数据处理。但涡旋本质上也是量子力学的，这表明，通过利用量子隧道和叠加，它们可能会以量子力学相干的方式被操纵。因此，该项目可能会导致量子信息技术设备的发展。拟议的项目与更好地理解和利用量子现象的国家目标是一致的。此外，它还将使学生掌握加入未来工业工作所需的专业知识，以实现和利用为量子信息技术建立的原理和技术。技术摘要本项目旨在探索固定在超导薄膜中图案孔上的薄膜涡旋的各种准静态和动态特性。垂直于薄膜的外部磁场将控制薄膜内的平均磁通密度，特别强调与整数占据相对应的强度。一类实验涉及搜索固定在孤立孔上的涡旋的共振响应，因为涡旋中心的移动会产生恢复力。此外，该项目还将研究应用DC的使用。脉冲电流，并与振荡场相结合，在相邻的孔对之间、沿着一维孔的直线或跨孔的二维阵列移动涡流，这将导致射频/微波发射，其频率由孔间距和局部电流密度控制。在跳频施加振荡电流应在直流传输特性中产生类似于Shapiro的阶跃。在相邻势垒之间存在量子隧穿的情况下，钉扎在势垒对上的单个涡旋可以对称或反对称的方式分布在势垒之间，由此可以形成两态叠加，这可以用光谱来寻找。这种旋涡的操作可用作通量流振荡器、计算机比特或数据存储元件。将被研究的现象，如果被实现，可能会潜在地导致新类型的超导设备，所有这些都是基于对孔钉扎涡流的操纵。这些包括：i)各种磁通流振荡器、多位磁通线存储元件，以及iii)可能的量子位。该项目的毕业生将有能力进入各种工业环境。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical AbstractSuperconductors, which transport electric current without loss, also expel a magnetic field. However, above some critical field magnetic flux enters a superconductor through the formation of an array of swirling currents of superconducting electrons, called vortices. The movement of these vortices can destroy the superconducting property. High field magnets avoid this problem due to microscopic defects that pin the vortices. Rather than having the vortices pinned randomly by defects, the approach of this research team is to pin them in a controlled way by creating patterns of nanoscopic holes within a thin film to which they attach. By introducing external electric and magnetic fields it should then be possible to move the vortices between the pinning sites in a controlled way. Such manipulations can, potentially, be used to either store data, perform calculations, or both, all within the same assembly of holes. Since vortices are inherently stable, being destroyed only at the edges of the film or on encountering an anti-vortex, the “information bits” they carry are secure. Furthermore, they can have sub micron dimensions and may respond on sub nanosecond time scales potentially facilitating high-speed, high density data processing. But vortices are also quantum mechanical in nature and this suggests the possibility they may be manipulated in a quantum mechanically coherent way by exploiting both quantum tunneling and superposition. Therefore, this project could lead to the development of devices for quantum information technology. The proposed project is in line with national goals to better understand and better exploit quantum phenomena. In addition, it will equip students with the expertise needed to join the work force of future industrial efforts to realize and exploit the principles and techniques established for quantum information technology.Technical abstractThis project aims to explore various quasi-static and dynamic properties of thin film vortices pinned on patterned holes in thin superconducting films. An external magnetic field perpendicular to the film will control the average flux density within the film, with special emphasis on strengths corresponding to an integer occupations. One class of experiments involves a search for resonant responses of vortices pinned on isolated holes, since displacement of the vortex center generates a restoring force. This project will in addition study the use of applied d.c. (or pulsed) currents, and in combination with oscillatory fields, to move vortices between neighboring pairs of holes, down a one-dimensional line of holes, or across a two dimensional array of holes, which should result in r.f./microwave emissions, the frequency of which is controlled by the hole spacing and the local current density. Application of an oscillatory current at the hopping frequency should produce Shapiro-like steps in the d.c transport characteristics. In the presence of quantum-tunneling between the neighboring potential wells, a single vortex pinned on the pair could distribute itself between the wells in a symmetric or antisymmetric manner from which two-state super-positions might be formed, which could be searched for spectroscopically. The manipulation of such vortices can be used as flux-flow oscillators, computer bits, or data storage elements. The phenomena to be examined, if realized, could, potentially, lead to new classes of super-conducting devices, all based on the manipulation of hole-pinned vortices. These include: i) various flux flow oscillators, a multi-bit flux line memory element, and iii) a possible qubit. Graduates of this program will be equipped to enter various industrial environments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.