Manipulation of Hole-pinned Vortices: Classical and Quantum

【非技术内容】超导体在无损耗传输电流的同时，也会产生磁场。然而，在某些临界场以上，磁通量通过形成一系列超导电子的旋流（称为涡流）进入超导体。这些涡旋的运动可以破坏超导特性。高磁场磁体避免了这个问题，因为它有固定涡流的微观缺陷。这个研究小组的方法不是让涡流被缺陷随机固定，而是通过在薄膜上创建纳米级孔的模式，以一种可控的方式固定它们。通过引入外部电场和磁场，就有可能以可控的方式在钉钉点之间移动涡流。这种操作可以潜在地用于存储数据，执行计算，或者两者兼而有之，所有这些操作都在同一个孔组合中进行。由于涡旋本身是稳定的，只有在薄膜边缘或遇到反涡旋时才会被破坏，因此它们所携带的“信息位”是安全的。此外，它们可以具有亚微米尺寸，并可能在亚纳秒的时间尺度上响应，从而促进高速、高密度的数据处理。但涡旋在本质上也是量子力学的，这表明它们可能通过利用量子隧道和叠加以量子力学相干的方式被操纵。因此，这个项目可能会导致量子信息技术设备的发展。拟议中的项目符合更好地理解和更好地利用量子现象的国家目标。此外，它将使学生具备加入未来工业努力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：本项目旨在探讨超导体薄膜中固定在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，特别强调与整数职业相对应的强度。一类实验涉及寻找固定在孤立孔上的涡流的共振响应，因为涡流中心的位移会产生一种恢复力。此外，本计画将研究应用直流（或脉冲）电流，并结合振荡场，在邻近的空穴对之间，沿一维空穴线，或穿过二维空穴阵列，移动漩涡，这将导致射频/微波发射，其频率由空穴间距和局部电流密度控制。在跳频处施加振荡电流会在直流输运特性中产生类似夏皮罗的阶跃。在相邻势阱之间存在量子隧穿的情况下，固定在势阱对上的单个涡旋可以以对称或反对称的方式分布在势阱之间，由此可能形成两态叠加，这可以通过光谱来搜索。这种旋涡的操纵可以用作流量振荡器、计算机位或数据存储元件。这种有待研究的现象，如果实现，可能会导致新型超导器件的产生，这些器件都是基于对孔钉涡流的操纵。这些包括：i)各种通量流振荡器，一个多比特通量线存储元件，和iii)一个可能的量子位。本课程的毕业生将具备进入各种工业环境的能力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.