Electric field spectroscopy of material defects in transmon qubits
Electric field spectroscopy of material defects in transmon qubits
复制标题
DOI：
10.1038/s41534-019-0224-1
复制
发表时间：
2019-11-22
影响因子：
7.6
通讯作者：
Ustinov, Alexey V.
中科院分区：
文献类型：
--
作者：
Lisenfeld, Juergen;Bilmes, Alexander;Ustinov, Alexey V.
超导集成电路在实现集成量子计算处理器方面显示出巨大的潜力。然而，固态方法的缺点是超导量子比特受到由器件材料中原子尺度缺陷引起的能量耗散和环境波动的强烈影响。进一步提高量子处理器的规模将需要改进器件制造技术，这需要用新的分析方法来指导，以了解和防止缺陷形成的机制。在这里，我们提出了一种通过外加电场调谐超导量子比特中的单个缺陷的技术。这提供了一种光谱方法来提取缺陷的能量分布、电偶极矩和相干时间。此外，它还使人们能够区分约瑟夫森结隧道势垒中的缺陷和电路界面上的缺陷。我们发现，在所研究的跨量子比特样品中，电路界面处的缺陷约占介电损耗的60%。在所有检测到的缺陷中，大约40%包含在阴影蒸发中平行发生的大面积寄生约瑟夫森结的隧道势垒中，只有大约3%被识别为强耦合缺陷，可能存在于小面积量子比特隧道结中。所展示的技术提供了一个有价值的工具来评估与电路接口和隧道结有关的消相干源，这很容易适用于标准量子比特样本。
Superconducting integrated circuits have demonstrated a tremendous potential to realize integrated quantum computing processors. However, the downside of the solid-state approach is that superconducting qubits suffer strongly from energy dissipation and environmental fluctuations caused by atomic-scale defects in device materials. Further progress towards upscaled quantum processors will require improvements in device fabrication techniques, which need to be guided by novel analysis methods to understand and prevent mechanisms of defect formation. Here, we present a technique to analyse individual defects in superconducting qubits by tuning them with applied electric fields. This provides a spectroscopy method to extract the defects' energy distribution, electric dipole moments, and coherence times. Moreover, it enables one to distinguish defects residing in Josephson junction tunnel barriers from those at circuit interfaces. We find that defects at circuit interfaces are responsible for about 60% of the dielectric loss in the investigated transmon qubit sample. About 40% of all detected defects are contained in the tunnel barriers of the large-area parasitic Josephson junctions that occur collaterally in shadow evaporation, and only approximate to 3% are identified as strongly coupled defects, which presumably reside in the small-area qubit tunnel junctions. The demonstrated technique provides a valuable tool to assess the decoherence sources related to circuit interfaces and to tunnel junctions that is readily applicable to standard qubit samples.