RAISE-TAQS: Symmetry Protected Quantum Bits through Fluxon Pairing

非技术描述：随着当前量子技术发展的步伐，超导量子计算机的实现正在快速接近。与经典计算机相比，量子计算机在一些与当今人类相关的最难解决的问题上提供了指数级加速计算的可能性。在过去的十年里，量子计算机的元素--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些进展，但已经表明，要提高量子比特的性能以实现实用的量子计算机，还有很长的路要走。本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比特，使其与环境解耦，并防止局部噪声。逻辑量子比特的基础是利用非平凡的对称性在硬件层面进行纠错，并在组成量子比特的电路中设计量子力学相互作用。这一研究项目有助于更好地理解如何利用某些通常在量子计算机中没有被利用的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旨在满足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需求很高，包括科技行业巨头和量子创业生态系统。这些活动包括介绍一系列针对早期物理和电气工程专业学生的量子信息科学入门短期课程，使他们在不断扩大的量子技术行业中获得机会。技术说明：该项目研究通过保护超导回路中通量子奇偶编码的量子态来实现高度相干量子比特的变革性想法。所提出的量子比特提供了纠错码的哈密顿实现，其中哈密顿量的基态可以被视为逻辑基态。在电路中实现完全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。该项目利用两个新开发的电路元件，基于电荷的量子干涉器件和超导电感，实现了受保护的磁通配对量子电路，即CoS(Phi/2)约瑟夫森元件，其最低能态因超导回路中的磁通奇偶而不同。预计这样的电路可以与本地噪声解耦，并在受保护状态下表现出很长的相干性。该项目的目标是：(1)通过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)进一步发展超导技术；(3)展示对通量对量子比特受保护状态的防止能量松弛和去相干的保护；(4)演示在状态准备和测量操作中在受保护状态和未受保护状态之间的快速绝热切换；以及(5)在亚微秒尺度上演示容错的单量子比特门操作和双量子比特门操作。该项目还支持研究生的教育，他们广泛接触到现代量子信息研究的最先进工具。这个由多个组成部分组成的教育和推广部分是该项目的重要组成部分，旨在开发一个培养未来量子电子工程师的计划。该奖项反映了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 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.