Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B41: New Techniques and Design in Superconducting Qubits IFocus Recordings Available
|
Hide Abstracts |
Sponsoring Units: DQI DMP DCMP Chair: Zlatko Minev, IBM Room: McCormick Place W-196C |
Monday, March 14, 2022 11:30AM - 11:42AM |
B41.00001: Laser-Annealing-Assisted Josephson Junction Resistance Tuning Hyunseong Kim, Alexis Morvan, Edward S Barnard, Maria Virginia P Altoe, William P Livingston, Yosep Kim, Larry Chen, Christian Juenger, John Mark Kreikebaum, D. Frank Ogletree, David I Santiago, Irfan Siddiqi As superconducting quantum devices increase in complexity, the Josephson junction critical current needs to be fabricated to higher precision. However, current fabrication processes often exhibit large dispersion between junctions, and can lead to frequency collisions amongst qubits in fixed-frequency transmon quantum processors. One effective post-fabrication technique for adjusting the frequency of transmons is laser annealing, which can reduce junction variability down to 0.15%, thereby increasing the number of working qubits in a quantum processor. We present a laser annealer for Josephson junctions based on conventional microscopy components. With this tool, we conduct a thorough study of the annealing parameters and demonstrate that we can tune our junctions up to 6%, which provides sufficient dynamic range to fine-tune our native 3% wafer-scale fabrication variations. We demonstrate that annealing is stable against temporal drifts (aging) and that annealing does not impact the material quality of our junctions. Finally, we investigate the coherence stability of transmons before and after annealing. We present two-level system (TLS) spectroscopy to observe how laser annealing affects the environment of these qubits. |
Monday, March 14, 2022 11:42AM - 11:54AM |
B41.00002: Measurement of the Low-Temperature Loss Tangent of High-resistivity Silicon Wafers with High-Q Superconducting Resonators Mattia Checchin, Daniil Frolov, Andrei Lunin, Anna Grassellino, Alexander Romanenko In this study, we present the first direct loss tangent measurement of high resistivity (100) silicon wafers in the milli-Kelvin regime. The measurement was performed by means of an innovative technique taking advantage of a high quality factor superconducting niobium resonator, that allows to achieve unprecedented level of accuracy. We report Si loss tangent values at the lowest temperature one order of magnitude larger than what typically expected, and we observe a non-monotonic trend of the loss tangent as a function of temperature. We report also an electric field dependence of the loss tangent not in agreement with TLS-type of dissipation. With this study, we established a new capability to directly measure the loss tangent of insulating materials with high accuracy and precision. This technique will allow to identify substrates and materials with low losses aiming to maximize coherence in quantum devices, and study the microwave dissipation of insulators in the quantum regime. |
Monday, March 14, 2022 11:54AM - 12:06PM |
B41.00003: Characterization of the Capacitance of Small Josephson Junctions from dc SQUID Resonances Bradley G Cole, Eric M Yelton, B.L.T. Plourde Developing techniques for characterizing and targeting the parameters of small-area Josephson junctions is important for implementing large superconducting qubit arrays. In particular, the self-capacitance of shadow-evaporated small area junctions is often challenging to extract, yet it plays an important role in the development of various topologically protected qubit designs. A dc SQUID allows for the extraction of individual junction capacitances via the measurement of the LC self-resonance in the current-voltage characteristic. By varying the dc SQUID geometry, as well as the critical current densities of the Al-AlOx-Al junctions that make up the SQUID, we can measure the behavior of the self-resonance and characterize the specific capacitance of these small Josephson junctions. |
Monday, March 14, 2022 12:06PM - 12:42PM |
B41.00004: Integrating superconducting quantum technology from the bottom up Invited Speaker: Katarina Cicak In the past decade, quantum system integration has driven innovation in device fabrication while balancing processes that could be detrimental to quantum information, like loss, noise, and decoherence. Today the thrust to connect and exploit the quantum in different physical realms is driving hybridization of basic superconducting (SC) components with a progressively broader set of devices. These integrated structures serve as resources for a growing quantum device toolbox and could be used for building future quantum networks, scaling quantum information processors, or studying basic quantum science. |
Monday, March 14, 2022 12:42PM - 12:54PM |
B41.00005: Direct Detection of Surface Spins using Superconducting Qubits David A Rower, Lauren Li, Lamia Ateshian, Bharath Kannan, Kyle Serniak, Dolev Bluvstein, Leon Ding, Aziza Almanakly, Jochen Braumuller, David K Kim, Alexander Melville, Bethany M Niedzielski, Jonilyn L Yoder, Mollie E Schwartz, Terry P Orlando, Joel I Wang, Simon Gustavsson, Riccardo Comin, William D Oliver Superconducting circuits are a promising platform for quantum sensing and information processing - applications which benefit from high coherence and minimal parasitic environmental coupling. A major impediment to realizing these traits is the presence of low-frequency magnetic flux noise which, in the case of flux-tunable qubits, promotes qubit dephasing. Flux noise is commonly blamed on the presence of paramagnetic surface environments created by adsorbed species such as molecular oxygen. We discuss the theory and experimental progress of high-sensitivity magnetic resonance experiments utilizing superconducting qubits with an applied in-plane magnetic field to detect parasitically coupled spins. Specifically, we focus on two categories of techniques: 1) passive techniques without spin excitation, and 2) active techniques that utilize spin excitation with local flux lines. Regarding passive methods, we discuss spin-locking and dynamical decoupling schemes. Regarding active methods, we implement local flux lines that strongly couple to native defects on the surface of SQUIDs and discuss schemes using either pulsed or continuous-wave surface spin driving. |
Monday, March 14, 2022 12:54PM - 1:06PM |
B41.00006: The Dielectric Dipper: a differential technique to measure dielectric loss tangents with high sensitivity Alexander P Read, Alexander P Read, Benjamin J Chapman, Chan U Lei, Kaicheng Li, Christopher J Axline, Luigi Frunzio, Robert J Schoelkopf Dielectric loss is suspected to be a major contributor limiting state-of-the-art superconducting qubit lifetimes. Recent experiments imply upper bounds on bulk dielectric loss tangents on the order of 10-7, but because these inferences are drawn from fully fabricated devices with many loss channels, it is difficult to know the actual dielectric loss tangents with a high degree of certainty. We have devised a method capable of separating and resolving dielectric loss with a sensitivity on the order of 10-8. We call our method the Dielectric Dipper, as the method involves the in-situ insertion of a dielectric sample into a high-quality cavity mode. Continuous variation of the sample’s participation in the cavity mode enables a highly selective differential measurement of dielectric loss. Our method probes the low-power behavior of dielectrics at cryogenic temperatures without the need for lithographic processes. This enables controlled comparison of isolated substrates and processing techniques. Such comparisons will inform designs and practices to better minimize dielectric loss. We present experimental comparisons of common dielectric substrates measured using this method. |
Monday, March 14, 2022 1:06PM - 1:18PM |
B41.00007: Epitaxial Merged-Element Transmon M. A Mueed, S. Rebec, B. A. Madon, N. Arellano, H. J. Mamin, M.H. Sherwood, M. Sandberg, R. M. Shelby, T. Topuria, E. Delenia, P. Rice, D. Rugar, M. Steffen, A. Pushp The merged-element transmon (MET), in which a Josephson junction with sufficiently large self-capacitance eliminates the need for a shunt capacitor, has recently gained much attention thanks to its compact design [1, 2]. Another potential benefit of MET is that the electric field lies predominantly inside the Josephson tunnel barrier, thus greatly reducing the effect of lossy interfaces which typically limit the standard transmon lifetime. In fact, the coherence lifetime of MET should primarily depend on the defect density within the tunnel barrier, meaning any improvement in the barrier quality can have a significant effect on qubit performance. For example, replacing the amorphous AlOx (the usual choice of tunnel junction in transmons) by an epitaxial barrier in a MET geometry should in principle reduce the relevant defect density and substantially improve qubit lifetime. Here we report preliminary results on epitaxially grown MET. We focus on qubit spectroscopy measurement with flux tunable METs to estimate the defect density within the epitaxial barrier. [1]. R. Zhao et al., Phys. Rev. Applied 14, 064006 (2020), [2] H. J. Mamin et al., Phys. Rev. Applied 16, 024023 (2021). |
Monday, March 14, 2022 1:18PM - 1:30PM |
B41.00008: Incorporation of hexagonal boron nitride into superconducting circuit elements John W Lyons, Param J Patel, Michael J Hatridge, Benjamin M Hunt Van der Waals (vdW) heterostructures, particularly those including hexagonal boron nitride (hBN), offer significant potential for the improvement of superconducting qubits. The nature of hBN as a stable tunnel barrier permits enhanced uniformity in tunneling current distribution, and its low dielectric loss could provide improved qubit coherence compared to traditional dielectric materials. Integrating vdW heterostructures into existing superconducting qubit architectures has the potential to enable enhanced qubit lifetimes and a more compact footprint. This talk will discuss our ongoing work in building and characterizing such devices. |
Monday, March 14, 2022 1:30PM - 1:42PM |
B41.00009: Quasiparticle Tunneling Suppression in Gap-Engineered Transmons Zachary Steffen, Yizhou Huang, Benjamin Palmer, Frederick C Wellstood For many superconducting qubits, non-equilibrium quasiparticles tunneling across the Josephson junction is suspected to be one of the dominant sources of energy relaxation. This loss mechanism is expected to be suppressed devices with junctions that are made from electrodes with sufficiently different superconducting gaps [1]. We have designed and fabricated an asymmetric Al/AlOx/Al/Ti transmon coupled to a 3D Al cavity. To do this, we deposited one pure Al electrode, oxidized it, and then deposited an Al/Ti bilayer as the counter-electrode. This process forms a standard AlOx tunnel barrier, but gives a ~100 μeV difference in superconducting gaps due to the Ti proximitizing the Al of the top layer. Fabrication of these devices, Giaever tunneling measurements of the small Al/AlOx/Al/Ti junction, as well as coherence measurements of the device will be discussed. |
Monday, March 14, 2022 1:42PM - 1:54PM |
B41.00010: Characterization of fabrication methods to reach high coherence superconducting quantum circuits Leon Koch, Niklas Bruckmoser, Leonhard Hölscher, Yuki Nojiri, Kedar Honasoge, Thomas Luschmann, Stefan Filipp The fabrication of highly coherent superconducting qubits is an important milestone on the way towards useful quantum processors. Although significant improvements in coherence time have been made over the last years, reaching qubit lifetimes well beyond 100 µs involves careful investigation of all fabrication steps. Here, we demonstrate that such high device qualities can be achieved by a combination of substrate cleaning, deposition optimization and post-process sample cleaning. We apply various characterization methods such as x-ray diffractometry, surface characterization and residual resistance measurements to optimize the quality of superconducting thin films. We also optimize ion milling, ozone descumming and metal interconnecting processes. Thereby, we reach quality factors well above 10^6 for thin-film aluminium and niobium CPW resonators and qubit lifetimes of at least 150 µs. |
Monday, March 14, 2022 1:54PM - 2:06PM |
B41.00011: A polymer-based spacer process for improved parameter targeting in 3D-integrated superconducting circuits Graham J Norris, Michael Kerschbaum, Jean-Claude Besse, Christopher Eichler, Andreas Wallraff Creating devices with hundreds of superconducting qubits is difficult on single-layer devices due to the large number of intra-die connections and impractical with multi-layer wiring processes due to their use of potentially lossy dielectrics. Instead, indium flip-chip bonding, a type of 3D-integration, can be used to join several single-layer superconducting dies, providing extra signal routing planes while avoiding deposited dielectrics. Although indium bump bonding of superconducting circuits has been successfully demonstrated [1, 2], precisely controlling the vertical chip spacing, which strongly affects circuit parameters such as resonator frequencies and qubit anharmonicities, without degrading the substrate surface remains a challenge [2]. Here we present a polymer hard-stop spacer fabrication process that provides deterministic inter-chip separation and benchmark the frequency reproducibility and internal loss rates of coplanar waveguide resonators. Since the flip-chip bonded die can significantly alter the electrical properties of circuit elements, we also characterize resonators with varying dimensions and discuss the implications of our results for large-scale devices. |
Monday, March 14, 2022 2:06PM - 2:18PM |
B41.00012: Mitigation of Superconducting Quantum Coherent Losses by Surface Passivation with Self-Assembled Monolayers Mohammed Alghadeer, Hussein Hussein, Saleem Rao, Hossein Fariborzi Quality factor of superconducting coplanar waveguide (CPW) microwave resonators is directly related to quantum coherence of superconducting circuits. Long coherence time is one of the key factors in realizing a commercial scale quantum computer and other related devices. The unique coupling of CPW resonators to other elements in quantum circuits is what forms the base of circuit quantum electrodynamics (cQED) architecture. While extensive research has explored techniques to reduce coherent losses of such devices, the precise structure of amorphous dielectric layers on surfaces and interfaces and their associated losses mechanism remain topics of active discussion. This is due to the presence of two-level system (TLS) oxides and non-TLS quasiparticles. In this work we present the design, fabrication and characterization of Niobium CPW resonators with a particular surface treatment using self-assembled monolayers (SAMs) that result in reducing superconducting losses. We show SAM-passivated resonators with more than 106 internal quality factors at single-photon-excitation power, measured at 100 mK, that have been probed using a suite of structural characterization tools (SEM, XPS and TEM) to show the efficiency of our surface treatment. We finally compare the improvements in quality factors to our numerical simulations. |
Monday, March 14, 2022 2:18PM - 2:30PM |
B41.00013: Investigating the impact of Nb2O5 on quantum coherence via selective oxygen scavenging Mahmut Sami KAVRIK, Shaul Aloni, David F Ogletree, Irfan Siddiqi, Adam Schwartzberg Implementation of superconducting qubit-based quantum processors is precluded prominently by the decoherence processes emerging from materials-inherent defects. The origin of these defects is yet to be understood, posing great urgency with the rise of quantum information science. The central question is the dielectric losses introduced by the formation of native oxides on Al and Nb used to build superconducting qubits. A recent study by our group on Nb oxidation indicates a strong impact of Nb suboxides on coherence times, where the microwave losses in qubits inversely scale with the thickness of the NbOx on Nb devices. While oxide is considered a primary effect for this improvement, DFT calculations by Griffin et. al., shown that sub-stoichiometric Nb2O5 has a paramagnetic phase that can be a source of the decoherence. In this study, we investigated the impact of Nb2O5 on coherence time by selectively eliminating Nb2O5 via oxygen scavenging by TiN grown with atomic layer deposition. TiN passivated resonators show traces of Nb2O5 while NbO and NbO2 persist on the Nb with native oxide according to photoemission spectroscopy. Selective reduction of Nb2O5 to NbO and mitigation of the associated defects suggests a viable step towards development of fault tolerant quantum processor. |
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