Dynamic Decoupling and Noise Characterization in Superconducting Qubits

超导量子比特(量子比特)是固态人造原子，由约瑟夫森隧道结、超导互连和微波谐振器组成。当冷却到毫开尔文温度时，这些超导电路表现出量子力学行为，例如取决于设计参数的磁通、电荷或结相的量子化状态。事实证明，这种超导人造原子是一种有用的工具，可以促进科学界对量子力学系统中相干的一般理解，特别是在天然原子和分子不易进入的区域。此外，超导量子比特是量子信息科学和技术应用的潜在候选者，包括量子计算。使用超导量子比特的主要限制因素是噪声，我们将研究和表征这些系统中的噪声源。核磁共振相关领域已建立的技术(如用于磁共振成像的技术)，例如被称为动态解耦和二维核磁共振波谱的靶向控制序列，将得到适应和推广。破坏这些超导量子比特量子性质的潜在微观来源将被识别和缓解。虽然量子信息科学和技术的未来应用仍在被认识中，但预计该技术本身(例如量子传感器、模拟机器)以及将出现的辅助衍生技术(例如材料、制造、控制方案)以及致力于将其变为现实的年轻研究人员将带来广泛的社会效益。这项工作的一个教育特点是学生可以进入和参与美国、日本和瑞典的学术(麻省理工学院、东京大学、查尔默斯大学)、企业(NEC)和政府(林肯实验室，RIKEN)的研究环境。通过共享研究和学生实习，这将提供一种文化，培养具有全球研究视角的年轻科学家，有能力发展和领导跨越机构和国际边界的跨学科团队。这项工作解决了先进的高相干超导量子比特中噪声源的表征、识别和缓解问题。一个目标是使用动态解耦等控制技术来评估和减轻新一代高级量子比特(具有高Q材料的2D和3D传输子，亚稳态通量量子比特)中的噪声。一般说来，这是使用基于核磁共振的技术来实现的，这些技术已知用于基准和阐明微观噪声发生器，以便识别和缓解消相干的潜在来源。我们的目标是了解是什么限制了他们的连贯时间。然后，这些信息可以用于改进制造工艺和材料。第二个目标是进一步推进噪声表征和缓解工具包。这项研究将利用具有任意幅度和相位的正交幅度调制器和序列发生器来产生微波脉冲序列，并将其应用于稀释式制冷机中的透子和亚稳态通量量子比特。相干表征，包括标准相干时间的测量，将作为量子比特量子化轴的函数来执行。随机基准测试、状态断层扫描和过程断层扫描将被用来表征闸门的保真度。消相干将通过应用动态解耦脉冲序列来缓解。这些技术也将被用来测量噪声功率谱密度。二维核磁共振波谱技术将被用来评估退相干的微观性质和来源。

Superconducting qubits (quantum bits) are solid-state artificial atoms, comprised of Josephson tunnel junctions and superconducting interconnects and microwave resonators. When cooled to milli-Kelvin temperatures, these superconducting circuits exhibit quantum mechanical behavior, such as quantized states of flux, charge, or junction phase depending on design parameters. Such superconducting artificial atoms have already proven a useful vehicle for advancing the scientific community's general understanding of coherence in quantum mechanical systems, particularly in regimes not easily accessible with natural atoms and molecules. Moreover, superconducting qubits are promising candidates for quantum information science and technology applications, including quantum computing. The main limiting factor in using superconducting qubits is noise, The sources of noise in these systems will be studied and characterized. Established techniques from the related field of NMR (such as those used in Magnetic Resonance Imaging), for example, the targeted control sequences known as dynamical decoupling and two-dimensional NMR spectroscopy, will be adapted and extended. The underlying microscopic sources that destroy the quantum nature of these superconducting qubits will be identified and mitigated. While the future applications of quantum information science and technology are still being recognized, a broad social benefit from the technology itself (e.g., quantum sensors, simulation machines) is anticipated, as well as from the the ancillary spin-off technologies that will arise (e.g., materials, fabrication, control schema), and the young researchers who work to make them a reality. An educational feature of this work will be the access and participation by students in academic (MIT, U. Tokyo, Chalmers), corporate (NEC), and government (Lincoln Laboratory, RIKEN) research environments in the US, Japan, and Sweden. Via shared research and student internships, this will provide a culture that fosters young scientists with a global research perspective, capable of developing and leading interdisciplinary teams across institutional and international boundaries. This work addresses the characterization, identification, and mitigation of noise sources in advanced, high-coherence superconducting qubits. One objective is to use control techniques such as dynamical decoupling to assess and mitigate noise in a new generation of these advanced qubits (2D and 3D transmons with high-Q materials, metastable flux qubit). In general, this is achieved using NMR-based techniques that are known to benchmark and elucidate microscopic noise generators in order to identify and mitigate the underlying sources of decoherence. The goal is to understand what is limiting their coherence times. The information can then be used to improve fabrication processes and materials. A second objective is further advance the noise characterization and mitigation toolset. The research will utilize a quadrature amplitude modulator and sequencer with arbitrary amplitude and phase to generate microwave pulse sequences, which will be applied to transmons and metastable flux qubits in a dilution refrigerator. Coherence characterization, including the measurement of standard coherence times, will be performed as a function of the qubit quantization axis. Randomized benchmarking, state tomography, and process tomography will be used to characterize gate fidelity. Decoherence will be mitigated through the application of dynamical decoupling pulse sequences. These techniques will also be used to measure the noise power spectral density. Two-dimensional NMR spectroscopy techniques will be used to assess the microscopic nature and origin of decoherence.