Department of Physics, King Fahd University of Petroleum and Minerals, Dhahran31261, Saudi Arabia.
Quantum Nanoelectronics Laboratory, Department of Physics, University of California, Berkeley, California94720, United States.
ACS Appl Mater Interfaces. 2023 Jan 11;15(1):2319-2328. doi: 10.1021/acsami.2c15667. Epub 2022 Dec 27.
Superconducting coplanar waveguide (CPW) microwave resonators in quantum circuits are the best components for reading and changing the state of artificial atoms because of their excellent coupling to quantum systems. This coupling forms the basis of the developing circuit quantum electrodynamic architecture. In quantum processors, oscillators are used to store and transmit quantum information using microwave-frequency wave packets. However, the presence of amorphous thin-film defects is deleterious and can result in an irrevocable loss of coherent information with uncontrolled degrees of freedom. Although there has been extensive research into techniques to reduce the coherent loss of such devices, the precise structure of amorphous dielectric layers on surfaces and interfaces and their associated loss mechanism are being actively studied. In particular, planar superconducting resonators are very sensitive to defects on their surfaces, such as two-level systems in oxidized metals and nonequilibrium quasiparticles, making these devices suitable probes for the different loss mechanisms. In this work, we present the design, fabrication, and characterization of Nb CPW resonators with different surface treatments with self-assembled monolayers (SAMs), which mitigate the growth of oxides in superconducting circuits. We demonstrate SAM-passivated resonators having internal quality factors of greater than 10 at a single-photon excitation power (measured at 100 mK), which were probed using scanning electron microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy to demonstrate the efficiency of our surface treatment. Finally, we compared the improvements in the experimental quality factors to those obtained by numerical simulation.
超导共面波导（CPW）微波谐振器在量子电路中是读取和改变人造原子状态的最佳元件，因为它们与量子系统有极好的耦合。这种耦合构成了发展电路量子电动力学体系结构的基础。在量子处理器中，振荡器用于使用微波频率的波包存储和传输量子信息。然而，非晶薄膜缺陷的存在是有害的，可能导致不可控制的自由度下相干信息的不可逆损失。尽管已经有大量研究用于减少此类器件的相干损耗的技术，但非晶介电层在表面和界面上的精确结构及其相关的损耗机制仍在积极研究中。特别是，平面超导谐振器对其表面上的缺陷非常敏感，例如氧化金属中的双能级系统和非平衡准粒子，这使得这些器件成为不同损耗机制的合适探针。在这项工作中，我们提出了具有不同表面处理的 Nb CPW 谐振器的设计、制造和特性，这些表面处理可以减轻超导电路中氧化物的生长。我们展示了具有大于 10 的内部品质因数的 SAM 钝化谐振器，在单光子激发功率下（在 100 mK 下测量），使用扫描电子显微镜、X 射线光电子能谱和透射电子显微镜来证明我们的表面处理的效率。最后，我们将实验品质因数的提高与数值模拟得到的结果进行了比较。
