RAISE-TAQS: Symmetry Protected Quantum Bits through Fluxon Pairing

非技术描述：以目前量子技术的发展速度，超导量子计算机的实现正在快速逼近。与经典计算机相比，量子计算机在解决当今与人类有关的一些最困难的问题时，提供了以指数速度计算的可能性。在过去的十年中，量子计算机的元件——量子比特（qubit）的性能有了巨大的提高。尽管在性能上取得了这样的进步，但事实证明，要想实现实用的量子计算机，提高量子比特的性能还有很长的路要走。该项目的目标是为量子计算机设计，制造和表征一类新的容错逻辑量子位，这些量子位与环境解耦并免受局部噪声的影响。逻辑量子比特是基于在硬件层面利用非平凡对称性和组成量子比特的电路中的工程量子力学相互作用进行纠错的。该研究项目有助于更好地理解如何利用量子计算机中通常未被利用的某些量子相互作用来提高量子比特的性能和可扩展性。该项目的教育推广部分解决了培养未来量子电子工程师的需求，这些工程师目前在量子技术行业（包括科技行业巨头和量子创业生态系统）中需求量很大。这些活动包括介绍一系列量子信息科学入门的短期课程，目标是物理和电气工程专业的学生在他们的职业生涯早期，让他们接触到不断扩大的量子技术行业的机会。技术描述：该项目研究了通过超导环路中磁通宇称编码的量子态的对称性保护来实现高度相干量子比特的变革性思想。所提出的量子比特提供了纠错码的哈密顿实现，其中哈密顿的基态可以被视为逻辑基态。在电路中实现一个成熟的拓扑保护量子态一直是难以捉摸的，主要是因为替代方法需要传统超导电路工具箱中没有的元素。本课题利用两种新开发的电路元件，基于电荷的量子干涉器件和一个超级电感器，实现了一个保护的通量对量子电路，一个cos（phi/2）约瑟夫森元件，其最低能态因超导环路中通量子的宇称而不同。期望这种电路能够从局部噪声中解耦，并在保护状态下表现出很长的相干性。该项目的目标是：(1)首先通过改进量子比特设计的对称性来增强Aharonov-Casher干涉，从而开发出高度相干的通量对量子比特；(2)进一步发展超导体技术；(3)论证了在保护态下对磁通对量子比特的能量松弛和去相干的保护；(4)为状态准备和测量操作演示受保护和无保护状态之间的快速绝热切换；(5)在亚微秒时间尺度上演示单量子位和双量子位门的容错操作。该项目还支持研究生的教育，这些研究生可以广泛接触到现代量子信息研究的最先进工具。多组件教育和推广组件是该项目的重要组成部分，旨在开发一个培训未来量子电子工程师的计划。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 description: With the current pace of quantum technology development, the realization of a superconducting quantum computer is fast approaching. Quantum computers offer the possibility for exponential speedup in computation in comparison to classical computers on some of the hardest problems relevant to humanity today. Over the past decade, the performance of the elements of a quantum computer, the quantum bit (qubit) has improved tremendously. Despite this progress in performance, it has been shown that there is still a long way to go in improving qubit performance to realize a practical quantum computer. The goal of this project is to design, fabricate, and characterize a new class of fault-tolerant logical qubits for a quantum computer decoupled from the environment and protected from local noises. The logical qubit is based on incorporating error correction at the hardware level utilizing nontrivial symmetries and engineering quantum mechanical interactions in the circuit which makes up the qubit. This research project contributes to a better understanding of how certain quantum interactions which have typically not been exploited in quantum computers can be utilized to improve qubit performance and scalability. The educational outreach portion of this project addresses the need to train future quantum electronics engineers for positions which are currently in high demand in the quantum technologies industry encompassing both tech industry giants and a quantum startup ecosystem. Such activities encompass the introduction of a series of short courses on introductory quantum information sciences targeted at physics and electrical engineering students early on in their careers, exposing them to opportunities in the ever-expanding quantum technology industry.Technical description: The project investigates transformative ideas of realizing highly coherent qubits through symmetry-protection of a quantum state encoded in the parity of fluxons in a superconducting loop. The proposed qubit provides a Hamiltonian realization of an error correction code where the ground states of the Hamiltonian can be regarded as the logical basis states. The realization of a full-fledged topologically protected quantum state in a circuit has been elusive primarily because alternative approaches have required elements not found in the conventional superconducting circuit toolbox. This project utilizes two newly developed circuit elements, the charge-based quantum interference device and a superinductor, to realize a protected fluxon-pairing quantum circuit, a cos(phi/2) Josephson element whose lowest-energy states are different by the parity of fluxons in a superconducting loop. It is expected that such a circuit could be decoupled from local noises and demonstrate very long coherence in the protected state. The objectives of this project are: (1) to develop a highly coherent fluxon-pairing qubit by first enhancing the Aharonov-Casher interference through symmetry improvements in the design of the qubit; (2) to further develop superinductor technology; (3) to demonstrate protection against energy relaxation and de-coherence in the protected state of the fluxon-pairing qubit; (4) to demonstrate fast adiabatic switching between the protected and unprotected states for state preparation and measurement operations; and (5) to demonstrate fault-tolerant single and two-qubit gate operations on the sub-microsecond time scale. The project also supports the education of graduate students who enjoy broad exposure to the state-of-the-art tools of modern quantum information research. The multi-component educational and outreach component, an essential part of the project, is designed to develop a program to train future quantum electronics engineers.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.