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 Y75: Superconducting Qubit Material Loss and CharacterizationFocus
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Sponsoring Units: DQI Chair: Corey Rae McRae, University of Colorado Boulder Room: Room 401/402 |
Friday, March 10, 2023 8:00AM - 8:36AM |
Y75.00001: Quasiparticle Poisoning of Superconducting Qubits from Resonant Absorption of Millimeter Wave Photons Invited Speaker: Chuan-Hong Liu The ideal superconductor provides a pristine environment for the delicate states of a quantum computer: because there is an energy gap to excitations, there are no spurious modes with which the qubits can interact, causing irreversible decay of the quantum state. As a practical matter, however, there exists a high density of excitations out of the superconducting ground state even at ultralow temperature; these are known as quasiparticles. Observed quasiparticle densities are of order 1 um-3, tens of orders of magnitude greater than the equilibrium density expected from theory. Nonequilibrium quasiparticles extract energy from the qubit mode and can induce dephasing. Here we show that a dominant mechanism for quasiparticle poisoning is direct absorption of high-energy photons at the qubit junction. We use a Josephson junction-based photon source to controllably dose qubit circuits with millimeter-wave radiation, and we use an interferometric quantum gate sequence to reconstruct the charge parity of the qubit. We find that the structure of the qubit itself acts as a resonant antenna for millimeter-wave radiation, providing an efficient path for photons to generate quasiparticles. A deep understanding of this physics will pave the way to realization of next-generation superconducting qubits that are robust against quasiparticle poisoning. |
Friday, March 10, 2023 8:36AM - 8:48AM |
Y75.00002: A Hybrid 3D Qubit Architecture for Probing Quantum Materials Ramya Suresh, Sheng-Wen Huang, Botao Du, Peter Salisbury, Jian Liao, Yong P. Chen, Leonid P Rokhinson, Ruichao Ma Superconducting quantum circuits are gaining traction as a platform for probing and characterizing new quantum materials due to their high coherence, strong coupling, and efficient control/readout. Using the tools of circuit QED, it is possible to explore material properties using coherent microwave photons at the single quantum level. We have designed and fabricated a transmon-like qubit with superconductor-TI-superconductor (S-TI-S) junctions in the 3D cavity architecture. The system is characterized by spectroscopic measurements, and time-domain measurements reveal coherence properties. The unconventional current-phase relationship in TI junctions could lead to noise resilience for certain decoherence channels. We discuss methods to realize frequency tunable 3D TI-Transmons by either using an on-chip voltage gate, or by forming an asymmetrical SQUID with one S-TI-S junction and one conventional S-I-S Josephson junction. Here, I will discuss our experimental progress, results, and future directions for using circuit QED devices for understanding new quantum materials. |
Friday, March 10, 2023 8:48AM - 9:00AM |
Y75.00003: 3D cavity characterization of niobium thin films in the quantum regime Bektur Abdistarov, Grigory Eremeev, Hani E Elsayed-Ali, Anna Grassellino, Alexander Romanenko Niobium thin films are the critical component to the majority of 2D superconducting qubit architectures. To isolate the loss channel associated with the intrinsic properties of niobium thin film, we studied niobium film deposited onto the inner surface of a high-Q (>1010) 3D bulk niobium cavity and investigated the microwave dissipation over a wide temperature range down to ~ 10 mK. Microwave measurements reveal that the intrinsic loss associated with the thin film is comparable to the bulk niobium loss. Structural microanalysis, chemical composition, and superconducting properties of the niobium thin films deposited with the same technique used for the cavity are conducted. Film annealing reduces surface oxides and shows a reduction in microwave loss, similar to the results observed with the bulk niobium cavities. |
Friday, March 10, 2023 9:00AM - 9:12AM |
Y75.00004: Extracting Contributions to Qubit Loss from Superconducting Microwave Resonators Shravan Patel, Spencer Weeden, Francisco Schlenker, Matthew Snyder, Emma Brann, Gabriel Spahn, David C Harrison, Chuan-Hong Liu, Abigail Shearrow, Robert McDermott Superconducting coplanar waveguide resonators play a critical role in information storage and qubit state measurement in superconducting quantum information processing. At the same time, these resonators are a versatile testbed for characterizing the various contributions to qubit loss. Ideally, the internal quality factors Qi of these resonators should reach ten million or higher, limited only by the loss tangent of the silicon or sapphire substrate. However, in real devices, Qi is limited by the presence of various loss channels, including two-level state (TLS) defects at amorphous interfaces, trapped magnetic flux vortices, and nonequilibrium quasiparticles. In this work, we measure Qi as a function of photon occupation in Al and Nb thin-film microwave resonators with different center conductor and gap widths. This allows us to extract the contribution to loss from interfacial TLS defects. We have also implemented novel resonator designs, including tapered resonators to study the relative contributions to loss from TLS and quasiparticles, and resonators with flux pinning structures to suppress the loss contribution from trapped flux. We have characterized devices fabricated on different substrates, used several methods to deposit the Al and Nb films, and explored various surface cleaning techniques to remove the native silicon oxide immediately prior to cooling the resonators. |
Friday, March 10, 2023 9:12AM - 9:24AM |
Y75.00005: Microwave vortex dynamics in superconducting granular aluminum resonators Clayton Larson, Kenneth R Dodge, Vito M Iaia, Eric Yelton, B.L.T. Plourde The high kinetic inductance of granular aluminum resonators presents a novel regime for studying vortex dynamics in superconductors. Vortices are quantized bundles of magnetic flux that penetrate through a superconductor for sufficiently large magnetic fields. Vortices trapped in regions of large microwave currents typically contribute excess loss for superconducting resonators and qubits. However, in highly disordered films, such as granular aluminum, we observe an anomalously low microwave loss due to vortices. We measure granular aluminum resonators at different magnetic field strengths, resonator frequencies, and temperature. We compare the vortex response in this system with that in more conventional superconducting films. |
Friday, March 10, 2023 9:24AM - 9:36AM |
Y75.00006: Characterizing microwave losses in superconducting quantum circuits: Part 1 Yanhao Wang, Suhas S Ganjam, Yao Lu, Archan Banerjee, Chan U Lei, Lev Krayzman, Kim Kisslinger, Chenyu Zhou, Yichen Jia, Mingzhao Liu, Luigi Frunzio, Robert J Schoelkopf The performance of superconducting quantum circuits has advanced tremendously in the past two decades, with coherence times increasing by over six orders of magnitude. In the past, improvements have been made by modifying circuit geometry; recently, improvements have been achieved through advancements in materials and processing. As coherence times continue to rise, it is becoming less apparent which loss mechanism dominates the total internal loss of transmon qubits and microwave resonators. In this talk, we will present a method using on-chip multimode microwave stripline resonators to distinguish between sources of loss in superconducting quantum circuits. We will measure loss factors associated with mechanisms such as bulk dielectric loss and surface loss, and demonstrate how they differ between various material platforms. |
Friday, March 10, 2023 9:36AM - 9:48AM |
Y75.00007: Characterizing microwave losses in superconducting quantum circuits: Part 2 Suhas S Ganjam, Yanhao Wang, Yao Lu, Archan Banerjee, Chan U Lei, Lev Krayzman, Kim Kisslinger, Chenyu Zhou, Yichen Jia, Mingzhao Liu, Luigi Frunzio, Robert J Schoelkopf The performance of superconducting quantum circuits has advanced tremendously in the past two decades, with coherence times increasing by over six orders of magnitude. In the past, improvements have been made by modifying circuit geometry; recently, improvements have been achieved through advancements in materials and processing. As coherence times continue to rise, it is becoming less apparent which loss mechanisms dominate the total internal loss of transmon qubits and microwave resonators. In this talk, we will demonstrate the power of loss characterization by using multimode stripline resonators to predict and verify the decay times of transmon qubits, and calculate their sensitivity to various sources of loss. In addition, we will discuss a pathway towards optimizing superconducting circuit design to realize on-chip quantum memories with coherence times approaching one millisecond. |
Friday, March 10, 2023 9:48AM - 10:00AM |
Y75.00008: Mitigating losses of superconducting qubits coupled strongly to defect modes Dante Colao Zanuz, Jean-Claude Besse, Quentin Ficheux, Alexei Orekhov, Laurent Michaud, Kilian Hanke, Ants Remm, Alexander Flasby, Christoph Hellings, Michael Kerschbaum, Nathan Lacroix, Stefania Lazar, Graham J Norris, Mohsen B Panah, François Swiadek, Sebastian Krinner, Christopher Eichler, Andreas Wallraff Energy relaxation in superconducting circuits is typically attributed to the coupling of qubits to a bath of material defects, which vary in nature, location and time. The defect modes show a large range of coherence times and coupling rates to qubits. Here, we investigate strategies to mitigate losses to the defects that couple strongly to the qubits, as they are particularly detrimental to the fidelities of operations relying on frequency excursions, such as the two-qubit controlled-phase gates. We report on the time and thermal-cycling dynamics of defect-mode configurations tracked for over 400 days in a single device. We also explore methods for fabricating qubits with a reduced number of strongly-coupled defect modes by changing the Josephson junction dimensions and the surface cleaning methods employed. Our results provide new insights into the properties of strongly-coupled defect modes and on strategies to mitigate loss of qubit coherence induced by those defects. The gained insights are invaluable for scaling up the number of qubits realized on devices for quantum information processing. |
Friday, March 10, 2023 10:00AM - 10:12AM |
Y75.00009: Dynamics of superconducting qubit coherence times due to fluctuations of two-level systems. Ivan Tsitsilin, Christian Schweizer, Franz Haslbeck, Federico Roy, Leon Koch, Max Werninghaus, Niklas Bruckmoser, Stefan Filipp Recent studies have shown that the stability of coherence times is strongly affected by two-level systems (TLSs). This is caused by chaotic frequency fluctuations of TLSs, which, when in proximity to the qubit resonance, significantly reduce its T1 times. Understanding and mitigating this behavior is crucial to realize functional quantum processing devices based on superconducting qubits. In this work, we perform a long-time stability analysis of the qubit T1 times as a function of qubit frequency utilizing the AC-Stark shifting technique [Carroll et al., arXiv:2105.15201]. We present an extensive analysis of the TLS distributions and their impact on T1 times for different qubit sample materials and RF line configurations. Furthermore, our results provide insight into the effect of the noise spectrum on the behavior and density of TLSs. |
Friday, March 10, 2023 10:12AM - 10:24AM |
Y75.00010: Non-equilibrium quasiparticle trapping in epitaxial Al-InAs Josephson junctions Bassel Heiba Elfeky, William M Strickland, James T Farmer, Sadman A Shanto, Azarin Zarassi, William F Schiela, Dylan Langone, Eli Levenson-Falk, Javad Shabani Planar epitaxial Al-InAs Josephson junctions (JJs) offer a unique platform for realizing tunable qubits and have shown signatures of topological superconductivity with the promise of hosting fault-tolerant qubits. In such high-transparency JJs, non-equilibrium quasiparticles can get trapped in the Andreev bound states of the junction, poisoning conduction channels. While quasiparticle poisoning can limit a parity-based qubit's coherence, it can also be harnessed to store information in the spin of a trapped quasiparticle forming a superconducting spin qubit. We study quasiparticle poisoning events by terminating a superconducting resonator to ground with an Al-InAs two-junction superconducting quantum interference device (SQUID). We investigate for signatures of quasiparticle poisoning in the resonant frequency of the resonator when the junction is flux-biased. Further, we perform continuous detection of these quasiparticle trapping events using time-domain measurements. Our results highlight the potential and limitations of quasiparticle poisoning in superconducting circuits based on Al-InAs JJs. |
Friday, March 10, 2023 10:24AM - 10:36AM |
Y75.00011: Quasiparticle dynamics in Andreev bound states part 1: phonon interactions James T Farmer, Sadman A Shanto, Azarin Zarassi, Andre Kuo, Eli Levenson-Falk Non-equilibrium quasiparticles in superconducting circuits can be a major source of error in both traditional and hybrid qubit platforms. In order to suppress these quasiparticles, it is necessary to learn more about their behavior. Quasiparticle dynamics in Andreev Bound States (ABS) are particularly interesting, as these provide a promising hybrid qubit platform. We present measurements of the dynamics of quasiparticles trapped in the ABS of a fully superconducting aluminum nanobridge Josephson junction. We focus on electron-phonon interactions leading to relaxation and excitation between the ABS and the bulk continuum of quasiparticle states. We find evidence for thermal processes and low-temperature saturation to multiple non-equilibrium processes. |
Friday, March 10, 2023 10:36AM - 10:48AM |
Y75.00012: Quasiparticle dynamics in Andreev bound states part 2: photon interactions Sadman A Shanto, James T Farmer, Azarin Zarassi, Andre Kuo, Leonid Glazman, Eli Levenson-Falk We measure the dynamics of quasiparticles trapped in the Andreev Bound States (ABS) of a fully superconducting aluminum nanobridge Josephson junction under the influence of microwave drive tones. We observe enhanced excitation of quasiparticles when the junction is driven and observe both expected and anomalous dependence on the drive power. We analyze our results in the context of a junction with multiple ABS and find evidence for inter-ABS transitions. |
Friday, March 10, 2023 10:48AM - 11:00AM |
Y75.00013: Quasiparticle Calorimetry using Dayem-Bridges Kevin M Ryan, Venkat Chandrasekhar Quasiparticle poisoning in superconducting qubits is believed to be a limiting factor on coherence times. Addressing this challenge is complicated by the difficulty of measuring quasiparticle populations while deep in the superconducting state. In this talk, we discuss a generation and detection scheme for quasiparticles based on thermal relaxation of mesoscopic Dayem-bridges. In such bridges, the IV characteristics depend largely on the thermalization of the superconducting weak link by the quasiparticle population of the superconducting banks, due to the vanishing thermal conductance of the banks and substrate at low temperature. By bringing the bridge into the normal state via current bias, and measuring the thermal relaxation lifetime back into the zero resistance state as a function of temperature or applied field, one performs a calorimetric measurement of the entire device with the bridge acting as both heater and thermometer. From this, the lifetime of quasiparticles which contribute to cooling the bridge may be obtained. We report on our experiments to demonstrate efficacy of this technique, and explore implications of quasiparticle lifetimes for superconducting qubit operation. |
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