Collaborative Research: Transmission of Quantum Information in Circuits of Superconducting Qubits

量子计算机有可能解决经典计算机完全不可能解决的问题，从国防密码学到人脸识别和药物开发。正如晶体管是所有现代数字电路的积木一样，量子比特(又名量子比特)是量子计算机的心脏。超导量子比特本质上是人造的二能级原子，可以使用集成电路技术设计和制造，它已经成为实现可扩展量子信息处理的首选方案之一。为了成功地进行量子计算，量子计算电路必须能够在大量高保真的量子比特之间快速传输量子信息。然而，由于现有的量子信息传输协议通常比单量子比特门慢一个数量级，量子信息传输已成为量子计算的瓶颈。此外，传统的QIT方法要么需要大量的片上面积，要么具有相对较低的品质因数，导致效率和保真度较低。因此，利用这些协议很难将量子比特电路放大到实际有用的大小。本项目的重点是演示超导量子比特电路中量子信息传输的一种新方法的基本原理。这种新的方法使用负电感超导量子干涉器件(NSQUID)的双轨阵列作为信息传输结构，大大改进了当前最先进的QIT协议。NSQUID分支之间的负互感将处理和传输量子信息的两个任务分配给nSQUID电路的不同部分，从而可以针对具体任务优化每个部分的参数，从而实现更快的QIT。因此，该项目的成功将消除建造量子计算机最关键的障碍之一。因此，从项目活动中获得的知识和见解可以很容易地应用于其他基于超导量子比特的量子计算电路。量子信息研究已成为一个竞争激烈的前沿研究领域，受到世界主要国家的积极追求。这对国家安全和保持美国在科学发现和技术创新方面的领导地位至关重要。这个量子电路物理理论和实验小组之间的合作项目为在科学探索的前沿之一的研究生和本科生的教育和培训提供了一个很好的机会。该项目还包括重要的外联和教育活动，例如改善在堪萨斯大学和石溪大学由NSF以前支持下开发的量子计算本科生和研究生课程；让本科生参与堪萨斯的量子信息研究；以及在当地高中、学院和大学举办量子信息座谈会。

Quantum computers have the potential to solve problems that are completely impossible for classical computers, ranging from cryptography for national defense to face recognition and drug development. Just as the transistor is the building block of all modern digital circuits, the quantum bit (aka the qubit) is the heart of a quantum computer. Superconducting qubits, which are essentially artificial two-level atoms that can be designed and fabricated using integrated circuit technology, have emerged as one of the top candidates for realizing scalable quantum information processing. In order to perform quantum computation successfully, quantum computing circuits must be able to transfer quantum information rapidly among a large number of qubits with high fidelity. However, because existing protocols for quantum information transfer (QIT) are in general an order of magnitude slower than single qubit gates, QIT has become the bottleneck for quantum computation. Furthermore, conventional methods of QIT either require a large amount of on-chip real estate or have relatively low quality factor leading to lower efficiency and fidelity. Therefore, it is difficult to scale up qubit circuits to a practically useful size with these protocols. The focus of this project is to demonstrate the basic elements of a novel method of quantum information transmission in superconducting qubit circuits. This new approach uses "dual-rail arrays of negative-inductance Superconducting QUantum Interference Devices (nSQUIDs)" as the information transmitting structures for significant improvement over the current state-of-the-art QIT protocols. The negative mutual inductance between the branches of an nSQUID assigns the two tasks of processing and transferring quantum information to different parts of the nSQUID circuit and therefore makes it possible to optimize parameters of each part for its particular task, so that much faster QIT can be achieved. The success of the project will thus remove one of the most critical roadblocks to building quantum computers. Therefore, knowledge and insights gained from the project activities can be readily applied to other superconducting qubit based quantum computing circuits.Quantum information research has emerged as a highly competitive cutting edge research field which is actively pursued by all major nations around the world. It is critically important to national security and to maintaining United States' leadership position in scientific discoveries and technological innovations. This collaborative project between theoretical and experimental groups in quantum circuit physics provides a good opportunity for education and training of the graduate and undergraduate students in one of the frontiers of scientific exploration. The project also includes significant outreach and education activities such as improving the undergraduate and graduate classes in Quantum Computing developed with previous NSF support at the University of Kansas and Stony Brook University; involving undergraduates into quantum information research at Kansas; and presenting colloquia on quantum information at local high schools, colleges and universities.