Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session S73: Superconducting Qubits: Surfaces, treatments, and two-level systems |
Hide Abstracts |
Sponsoring Units: DQI Chair: Kristiaan De Greve, IMEC Room: Room 405 |
Thursday, March 9, 2023 8:00AM - 8:12AM |
S73.00001: TLS loss in room-temperature-nucleated alpha-Ta resonators Loren D Alegria Like Niobium, Tantalum has demonstrated utility as a metallization layer within microfabricated superconducting quantum information processors. But, unlike Nb, high temperatures must be used to ensure the formation of the bcc (alpha) phase of the pure metal. It is known that a thin Nb layer can nucleate the growth of alpha-Ta at room temperature, but the precise qualities of nucleated films remain unclear. We perform a side-by-side comparison of nucleated and non-nucleated films patterned into resonators. We observe moderately greater TLS densities in nucleated Ta films as compared to pure Ta, consistent with higher defect densities evident in electron microscopy, but we suggest that this difference may be tolerable for substrates or processes that cannot withstand high temperatures. |
Thursday, March 9, 2023 8:12AM - 8:24AM |
S73.00002: Microscopic loss sources in alpha-tantalum superconducting resonators grown on silicon Daniel Perez, Massimo Mongillo, Xiaoyu Piao, Sebastien Couet, Danny Wan, Yann Canvel, A. M. Vadiraj, Tsvetan Ivanov, Jeroen Verjauw, Rohith Acharya, Jacques Van Damme, Fahd A Mohiyaddin, Pallavi Gowda, Antoine Pacco, Bart Raes, Julien Jussot, Joris Van de Vondel, Anton Potocnik, Iuliana P Radu, Bogdan Govoreanu, Kristiaan De Greve, Johan Swerts The performance of state-of-the-art superconducting quantum devices is currently limited by microwave dielectric losses at different surfaces and interfaces. The use of alpha-tantalum in these devices leads to a reduction in their dielectric loss and to an improvement of device performance due to its thin low-loss oxide. However, this tantalum phase was so far realized only on sapphire substrates, which is incompatible with advanced processing in industry-scale fabrication facilities. Here, we demonstrate the fabrication of alpha-tantalum resonators directly on a silicon wafer over a variety of metal deposition conditions, achieving internal quality factors up to five million at low photon number. Complementarily, we combine a comprehensive device material characterization study including, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy and resistivity, with resonator loss modelling and simulation. By comparing experimental and simulated resonator loss, we demonstrate that two-level-system loss is dominated by surface oxides contributions. Our study paves the way to large scale manufacturing of low-loss superconducting circuits and to materials-driven advancements in superconducting circuit performance. |
Thursday, March 9, 2023 8:24AM - 8:36AM |
S73.00003: Nb encapsulation studies for improved superconducting qubit coherence Mustafa Bal, Francesco Crisa, Shaojiang Zhu, Akshay A Murthy, ZuHawn Sung, Jaeyel Lee, Daniel Bafia, David van Zanten, Ivan Nekrashevich, Tanay Roy, Grigory Eremeev, Roman Pilipenko, Florent Q Lecocq, Michael R Vissers, Jose Aumentado, Joel N Ullom, Peter Hopkins, Alexander Romanenko, Anna Grassellino A thin naturally forming layer of surface oxides of Nb is believed to be a significant source of decoherence in Nb based superconducting qubits. Here, we coat the Nb surface with 5 to 10 nm of passivation layer to inhibit the formation of Nb oxides. A wide range of materials has been explored as the passivation layer to include Al, Ta, and TiN, to name a few. We report the results of microwave loss measurements of superconducting transmission line resonators and coherence measurements of transmon qubit devices. Preliminary results indicate a correlation between microwave loss and coherence measurements. Supported by materials characterization tools, a systematic investigation is launched to help identify causes of microwave loss and decoherence, and converge on materials/passivations to mitigate loss mechanisms. This material is based upon work supported by the U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, Superconducting Quantum Materials and Systems Center (SQMS) under contract number DE-AC02-07CH11359. |
Thursday, March 9, 2023 8:36AM - 8:48AM |
S73.00004: Nb surface encapsulation to improve resonators quality factor Francesco Crisa, Mustafa Bal, Shaojiang Zhu, Akshay A Murthy, ZuHawn Sung, Jaeyel Lee, Daniel Bafia, David van Zanten, Grigory Eremeev, Ivan Nekrashevich, Roman Pilipenko, Anna Grassellino, Alexander Romanenko, Florent Q Lecocq, Michael R Vissers, Joel N Ullom, José Aumentado, Peter Hopkins, Antony McFadden, Corey Rae McRae, David Olaya Nb qubits relaxation time are limited by the Nb2O5 layer at the metal air interface. This study is aimed to limit the formation of the oxide layer, encapsulating the Nb surface with other superconducting materials such as Ta, TiN and Re or with dielectric materials. To better understand the results, we are realizing these studies on coplanar waveguide resonators where the relation between surface losses and quality factor is clear. |
Thursday, March 9, 2023 8:48AM - 9:00AM |
S73.00005: Elemental Semiconductor Encapsulation of Niobium Thin Films for Superconducting Qubits Dominic P Goronzy, Carlos G G Torres Castanedo, Anthony Q McFadden, Corey Rae H McRae, Thang Pham, David Garcia-Wetten, Mitchell J Walker, Nikolay Zhelev, Hong Youl Park, Vinayak P Dravid, Michael J Bedzyk, Mark C Hersam Niobium is a widely used material for the fabrication of superconducting qubits, however it readily forms an amorphous native oxide. This amorphous native oxide, primarily composed of Nb2O5 but including other sub-oxides, has been shown to be a source of two-level systems (TLSs) and loss that result in decoherence.1 In this study we explore encapsulation of Nb with elemental semiconductor materials. Based on materials loss measurements, amorphous Si is lower loss than Nb2O5 and this trend is extended even further with amorphous Ge, which is measured to have low loss in comparison to a large range of materials.2,3 We explore a range of deposition methods for Si and Ge, including thermal and e-beam evaporation and pulsed laser deposition. Furthermore, we explore the effects of encapsulating Nb before ambient exposure vs oxide removal and subsequent encapsulation in later processing. X-ray diffraction, X-ray reflectivity, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and transmission electron microscopy techniques are used to characterize the materials interfaces and validate the effectiveness of Nb2O5 exclusion. |
Thursday, March 9, 2023 9:00AM - 9:12AM |
S73.00006: Improvement of the superconducting qubit lifetime with the surface passivation technology Shaojiang Zhu, Mustafa Bal, Francesco Crisa, Akshay A Murthy, ZuHawn Sung, Jaeyel Lee, Daniel Bafia, David Zanten, Grigory Eremeev, Ivan Nekrashevich, Roman Pilipenko, Anna Grassellino, Alexander Romanenko, Florent Q Lecocq, Michael R Vissers, Joel N Ullom, Jose Aumentado, Peter Hopkins, Tanay Roy It is well known that the two-level systems (TLSs) existing in the amorphous surface/interface oxides of the metal pads are the main decoherence source of the superconducting quantum devices. There are a few ways to remove the surface oxides in order to improve the microwave loss; One of the straightforward methods is to encapsulate the metal pads with another low loss thin metal, such as Ta or TiN, which has less oxidation in the atmosphere. In this work, we present our measurements on the Nb-based superconducting transmon qubits with different surface passivation technologies. We clearly show the improvement of the qubit coherence if carefully choosing the encapsulating materials, which is indicative that the surface TLS losses are effectively suppressed with encapsulation. We benchmark the qubit energy relaxation and discuss the instabilities of the TLSs resonating near the qubit frequency. |
Thursday, March 9, 2023 9:12AM - 9:24AM |
S73.00007: Niobium Hydride Evolution and Phase Equilibrium in Niobium Capping Layers Tyler J Leibengood, Graham Pritchard, Peter W Voorhees, James M Rondinelli, P-C A Simon Niobium is currently being used in superconducting qubit development. Hydrogen diffuses into bulk Niobium during processing when a passivating layer is absent. Hydrogen contamination causes "hydrogen Q disease" which drastically degrades the superconducting properties of the device. This degradation has been attributed to non-superconducting hydride precipitation at cryogenic temperatures [1]. Elastic energy is expected to impact precipitate formation and equilibrium shape. The hydride stiffness tensor calculated with density functional theory (DFT) and misfit strains are combined in the free energy functional of a phase field model. The elastically soft directions of the hydride and bulk niobium are found to be of type and respectively in the niobium coordinate system. The diffusion coefficient of hydrogen in niobium at -68 °C causes nano-scale hydrides to reach equilibrium on the order of milliseconds. When in proximity of a free surface, precipitates migrate toward the free surface and coarsen while incorporated precipitates dissolve. TiN and Si are currently under consideration for capping layers. In the interest of determining possible stable intermediate phases at the interface the CALPHAD method is used to produce ternary phase diagrams for the TiN-O-Nb and Si-O-Nb systems. |
Thursday, March 9, 2023 9:24AM - 9:36AM |
S73.00008: Mitigation of Interface Losses in Transmon Qubits Using Hydrofluoric Etches Michael A Gingras, Kyle Serniak, Greg Calusine, David K Kim, Alexander Melville, Ali Sabbah, Kate Azar, Wayne Woods, Jeffrey Knecht, Bethany M Niedzielski, Cyrus F Hirjibehedin, Mollie E Schwartz, Jonilyn L Yoder, William D Oliver Superconducting transmon qubits, a promising hardware platform for quantum computing applications, have developed from proof-of principle single-bit demonstrations to mature deployments of many-qubit quantum processors. Reducing losses in superconducting qubit circuits is critical to further the development of large-scale transmon architectures. In this talk we discuss the potential of hydrofluoric etches to remove lossy silicon oxides in close proximity to sensitive circuit elements such as Josephson Junctions, resonators and crossover tethers. This etch can be implemented at several different process points during the fabrication of these elements with little to no damage to existing structures. The results and future potential of these etches will be discussed. |
Thursday, March 9, 2023 9:36AM - 9:48AM |
S73.00009: The dielectric dipper: experimental comparisons of common dielectric substrates in isolation Alexander P Read, Benjamin J Chapman, Luigi Frunzio, Robert J Schoelkopf We have devised a method for characterizing bulk dielectric loss with a sensitivity on the order of 1e-8. The method probes the low-power behavior of dielectrics at cryogenic temperatures without the need for lithographic processes. So far, the method has identified bulk loss as a major source of decoherence of transmon qubits on EFG sapphire. With a bulk loss tangent of 6e-8, bulk loss in EFG sapphire places a limit on transmon lifetime of about 800 us. Using the same technique, we investigate other substrate materials and processes with the aim to better quantify dielectric loss, understand its origin, and determine how it can be mitigated in fabrication of superconducting quantum devices. |
Thursday, March 9, 2023 9:48AM - 10:00AM |
S73.00010: Surface processing of niobium cavities for quantum computing Engin Ciftyürek, Nitzan Kahn, Ofir Milul, Fabien Lafont, Zheshen Li, Serge Rosenblum Niobium (Nb) superconducting cavities hold great promise for implementing quantum memories due to their high-quality factors. However, a major obstacle towards this goal is oxidation of the Nb surface, which drastically decreases the cavity quality factors due to two-level defects within the amorphous niobium oxides. The resulting photon dissipation can be prevented by application of chemical and thermal treatments of the cavity surface. In this work, we perform an in-depth characterization of the oxidation state and crystallinity, of the niobium oxide as a function of depth and temperature. We discuss novel surface treatment methods, and correlate them with the resulting single-photon lifetimes. |
Thursday, March 9, 2023 10:00AM - 10:12AM |
S73.00011: Argon milling induced loss mechanisms in superconducting quantum circuits Jacques Van Damme, Anton Potocnik, Kristiaan De Greve, Tsvetan Ivanov, Jeroen Verjauw, Rohith Acharya, Daniel Perez Lozano, Vadiraj Manjunath Ananthapadmanabha Rao, Paola Favia, Massimo Mongillo, Danny Wan, Jo De Boeck The fabrication of superconducting circuits requires multiple deposition, etch and cleaning steps, each possibly introducing material property changes and microscopic defects. In this work we specifically investigate the process of argon milling on niobium and aluminum as a potential coherence limiting process. We find that niobium microwave resonators show an order of magnitude decrease in quality-factors after surface argon milling, while aluminum resonators are resilient to the same process. We characterize the Nb surface with XPS, AFM, and STEM. The argon milled niobium surface regrows a layered oxide structure of primarily Nb2O5 causing an increase in both two-level-system defect losses and residual losses. Two-tone spectroscopy measurements reveal increased two-level-system electrical dipole moments of the average tunneling defect at the argon milled niobium surface. A carefully timed etch fully removes the induced losses and shows a path towards state-of-the-art overlap Josephson junction based qubits on niobium. |
Thursday, March 9, 2023 10:12AM - 10:24AM |
S73.00012: Reduction of Coherent Losses using Molecular Self-assembled Monolayers at Interfaces of Superconducting Quantum Circuits Mohammed Alghadeer, AHMED HAJR, Archan Banerjee, Kyunghoon Lee, Hussein Hussein, Hossein Fariborzi, Saleem Rao, Irfan Siddiqi Defects at different interfaces in circuit quantum electrodynamics (cQED) systems - in particular, two-level-system (TLS) defects - contribute significantly to decoherence, ultimately limiting the performance of quantum computation and sensing. These defects cannot be ousted in conventional way, i.e. by depositing an inorganic passivating layer, because such additional layers can worst these interfaces. Chemisorption of self-assembled monolayers (SAMs) on metal and oxide is a promising option to engineer the desired properties of such interfaces. SAMs bonding strength and many more related properties are well established for more than a decade. In cQED etching can remove defects from air-interfaces however, their regrowth remains a problem. Here, we used SAMs to stop the regrowth of defects and observed sustained improvement in quality factor of the superconducting co-planer waveguide (CPW) resonators. We will present improvement in quality factor of CPW due to SAM and correlate the results to materials analysis, including TEM, SEM, AFM and XPS, which confirms that SAMs stop the regrowth of oxides and provide sustained improvement in the performance of superconducting quantum circuits. |
Thursday, March 9, 2023 10:24AM - 10:36AM |
S73.00013: Detailed Structural and Chemical Analysis of Amorphous Compounds in Superconducting Qubit Systems Akshay A Murthy, Cameron J Kopas, Stephanie M Ribet, Josh Y Mutus, Lin Zhou, Matthew J Kramer, Anna Grassellino, Roberto dos Reis, Vinayak P Dravid, Alexander Romanenko Following improvements in device coherence times and gate fidelities over the past two decades, defects, impurities, and interfaces have emerged as the key barriers currently limiting the performance of superconducting quantum systems. As experimental and theoretical investigations have suggested that deviations from crystalline order can lead to quantum decoherence, we use a combination of scanning transmission electron imaging and diffraction methods to interrogate the thin metal films integral for superconducting qubit operation. Specifically, we investigate disordered compounds at the metal/air and metal/substrate interfaces. We observe that highly disordered regions in the oxide that forms at the surface of the niobium film are more likely to contain oxygen vacancies and exhibit weaker bonds between the niobium and oxygen atoms. Additionally, at the interface between niobium and the underlying silicon substrate, we observe an amorphous alloyed region that exhibits variations in stoichiometry and bond distances. We hypothesize that each of these features may contribute to quantum decoherence. Equipped with these findings, we seek to engineer the atomic ordering in these regions to intelligently fabricate superconducting qubits and extend coherence times. |
Thursday, March 9, 2023 10:36AM - 10:48AM |
S73.00014: Characterization of Transmon Qubits with Low-loss Parallel Plate Capacitors Katrina M Sliwa, Alexander Melville, Wayne Woods, Kyle Serniak, Thomas M Hazard, Evan Golden, David K Kim, Bethany M Niedzielski, Michael Gingras, Kaidong Peng, Kevin P O'Brien, Jonilyn L Yoder, Mollie E Schwartz, William D Oliver We have developed Al-AlOx-Al capacitors for use in superconducting circuits. They offer high specific capacitance (~12 fF/µm2), low loss (tan?? ~ 2x10-6), high reproducibility (<2% over 2" wafer), and allow for a large reduction in footprint relative to traditional co-planar (lateral) capacitors. In this talk we discuss the coherence properties and two-level system (TLS) densities of transmon qubits fabricated with varying degrees of low-loss parallel plate capacitor participation, and the implications for using these types of capacitors in qubits and other superconducting quantum circuits. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700