Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F16: Superconducting Qubit Materials, Fabrication, and Coherence I |
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Sponsoring Units: DQI Chair: Corey Rae McRae, National Institute of Standards and Technology Boulder Room: 201 |
Tuesday, March 3, 2020 8:00AM - 8:12AM |
F16.00001: T1 of transmons with electrodes that have different gaps. Kungang Li, Frederick C Wellstood, Christopher J Lobb, Sudeep Dutta, Rui Zhang, Shahriar Keshvari, Dylan Poppert Using double-angle evaporation we fabricated a transmon which had one electrode formed by deposition of nominally pure aluminum and the counter-electrode formed by deposition of oxygen-doped aluminum. On the same sapphire chip, during the same pump-down of the evaporator we deposited a second transmon with both electrodes made from nominally pure aluminum. The energy gaps of the electrodes depend on the film thickness and the grain size, which is affected by the oxygen doping. Measurements of the relaxation time T1 of the first device at 10 mK revealed a typical lifetime of about 200 microseconds while the second device had a typical T1 of about 90 microseconds. When T1 was measured as a function of temperature up to 300 mK, the two devices showed significantly different onset temperatures for the appearance of thermal quasiparticles. We compared our T1 vs T results to a model based on the behavior of nonequilibrium quasiparticles residing in the electrodes and extracted the energy gap and the density of the non-equilibrium quasiparticles. |
Tuesday, March 3, 2020 8:12AM - 8:24AM |
F16.00002: Power and temperature dependence of High Q superconducting resonators Ashish Alexander, Christopher Weddle, Christopher Richardson An integrated power and temperature dependent model of resonator quality factor predicts loss contributions from two-level systems and quasiparticles simultaneously. At millikelvin temperatures, in the presence of external power, the weak electron-phonon coupling between the phonons and quasiparticles may lead to quasiparticles thermalizing at a different temperature than phonons. |
Tuesday, March 3, 2020 8:24AM - 8:36AM |
F16.00003: Integration of InAs-Al Heterostructures into Microwave Circuit Joseph Yuan, Matthieu Dartiailh, William Mayer, Noah Goss, Tri D Nguyen, Kaushini S Wickramasinghe, Kasra Sardashti, Javad Shabani Semiconductor-based Josephson junctions provide a platform to study the proximity effect and for the realization of topological superconductivity. Recently our group has demonstrated the possibility of having highly transparent contact between a superconductor and a semiconductor by combining high mobility Indium Arsenide (InAs) surface two dimensional electron gases (2DEGs) with epitaxially grown aluminum (Al) [1]. This allows for gate-tunable superconducting Josephson Junctions and consequently gate-tunable Transmons [2]. Here we present the integration of these InAs-Al heterostructures into microwave circuits such as Gatemon Qubits. The steps needed to fabricate on III-V material platform while mitigating microwave losses and microwave response will be discussed. |
Tuesday, March 3, 2020 8:36AM - 8:48AM |
F16.00004: Preprocessing Method for Microwave Resonator Fitting Keegan Mullins, Corey Rae McRae, David Pappas, Josh Y Mutus, Haozhi Wang, David Fork We present a preprocessing method for S21 data from superconducting microwave resonators. In the field of quantum computing, it is becoming increasingly necessary to charactarize loss in superconducting circuits to a higher degree of accuracy. The goal of the code implemented is to provide a rigorous standard for charactarizing this loss. The method is implemented in python where the Diameter Correction Method, Inverse S21 method and Closest Pole and Zero method are all used in conjunction with the preprocessing. Accuracy of the preprocessing method is tested by comparing results from computer simulated resonator data from circuit elements to calculated values from the circuit elements of the simulated data. The preprocessing method entails a removal of the S21 data background by linear fit of the end points for both magnitude and phase, as well as the option to remove background from a user background file (a dataset of the same format without resonator behavior to establish a baseline). Testing the preprocessing method across varying parameters of circuit elements allows us to view correlation between preprocessing and error in determination of parameters. |
Tuesday, March 3, 2020 8:48AM - 9:00AM |
F16.00005: Materials Engineering in Superconducting Qubits Alexander Place, Basil M Smitham, Lila Rodgers, Pranav Mundada, Mattias V Fitzpatrick, Sara Sussman, Anjali Premkumar, Jacob Bryon, Berthold Jaeck, Guangming Cheng, Harshvardhan Babla, Trisha Madhavan, Austin Ferrenti, Andras Gyenis, Robert J. Cava, Nan Yao, Nathalie De Leon, Andrew Houck During the early days of superconducting qubits, increases in coherence times were frequently driven by improvements in materials and fabrication techniques. More recent advances have focused on manipulating capacitive, inductive, and Josephson energy scales, as well as engineering favorable qubit environments. In this talk we again focus on materials engineering of qubits. We explore how new materials and surface treatments can improve coherence times. Furthermore, we correlate the results of materials spectroscopy and time domain measurements to provide insight into relaxation mechanisms. |
Tuesday, March 3, 2020 9:00AM - 9:12AM |
F16.00006: Observation of individual two-level defects at material surfaces using circuit QED Timothy Kohler, Chih-Chiao Hung, Kevin Osborn, Neda Forouzani
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Tuesday, March 3, 2020 9:12AM - 9:48AM |
F16.00007: 3D Integration to Enable High Coherence and Connectivity for Superconducting Qubits Invited Speaker: Danna Rosenberg As superconducting qubit systems gets larger, it will become increasingly important to use 3D integration to address arrays of qubits. I will present our work developing and characterizing 3D integration components, focusing on superconducting through-silicon vias (TSVs), and I will discuss recent demonstrations incorporating superconducting TSVs in qubit control and readout circuitry. |
Tuesday, March 3, 2020 9:48AM - 10:00AM |
F16.00008: The dielectric dipper: a differential technique to measure dielectric loss tangents with high sensitivity Alexander P Read, Kaicheng Li, Benjamin J. Chapman, Chan U Lei, Vijay Jain, Christopher Axline, Luigi Frunzio, Robert Schoelkopf Dielectric loss is suspected to limit superconducting qubit lifetimes. This could be tested by a measurement capable of detecting bulk dielectric loss smaller than the bound inferred from recent experiments (i.e., loss tangent less than 10-7). We have devised a method for characterizing bulk dielectric loss with a sensitivity on the order of 10-8. The method is compatible with cryogenic temperatures and single-photon powers and does not require lithographic processes. This allows for rapid comparison of isolated substrates, processing techniques, and their statistical variations. Such comparisons will inform designs and practices to better minimize dielectric loss. We present experimental comparisons of common dielectric substrates measured using this method. |
Tuesday, March 3, 2020 10:00AM - 10:12AM |
F16.00009: Transmon qubit in a magnetic field: Evolution of coherence and transition frequency Martin Weides, Andre Schneider, Tim Wolz, Marco Pfirrmann, Martin Spieker, Hannes Rotzinger, Alexey V. Ustinov We report on spectroscopic and time-domain measurements on a fixed-frequency concentric transmon qubit in an applied in-plane magnetic field to explore its limits of magnetic field compatibility. We demonstrate quantum coherence of the qubit up to field values of B=40mT, even without an optimized chip design or material combination of the qubit. The dephasing rate Γφ is shown to be unaffected by the magnetic field in a broad range of the qubit transition frequency. For the evolution of the qubit transition frequency, we find the unintended second junction created in the shadow angle evaporation process to be non-negligible and deduce an analytic formula for the field-dependent qubit energies. We discuss the relevant field-dependent loss channels, which cannot be distinguished by our measurements, inviting further theoretical and experimental investigation. Using well-known and well-studied standard components of the superconducting quantum architecture, we are able to reach a field regime relevant for quantum sensing and hybrid applications of magnetic spins and spin systems. |
Tuesday, March 3, 2020 10:12AM - 10:24AM |
F16.00010: Design of The Merged Element Transmon Qubit Sungoh Park, Ruichen Zhao, Corey Rae McRae, Junling Long, Tongyu Zhao, Russell Lake, Mustafa Bal, Haozhi Wang, David Pappas Transmon qubits are one of the most promising candidates for building a universal quantum processor. They consist of two discrete elements: a nanoscale Josephson junction (JJ) and a coplanar capacitor. In conventional transmon designs, the plates of the shunt capacitor have to be very large to achieve low participation ratio of the lossy interfaces. To circumvent this issue, we propose to engineer the device so that the electric field distribution is confined to junction dielectric by merging the capacitor and JJ into a single superconductor/dielectric/superconductor trilayer structure such that the frequency, anharmonicity, and Ej/Ec parameters are in the transmon regime. We refer to this architecture a mergemon to distinguish it from conventional designs. We explore different low-loss dielectrics such that the trilayer itself would provide not only the nonlinear inductance but also most of the capacitance of the transmon qubit. By FEM based simulation, we design the mergemon qubit-readout resonator to be in the strong dispersive regime. We also verify that this design can be realized with standard optical lithography process. Finally, we also discuss possibility of leveraging the state-of-the-art molecular-beam epitaxy technology to enhance the coherence of the mergemon. |
Tuesday, March 3, 2020 10:24AM - 10:36AM |
F16.00011: Improving the performance of superconducting coplanar waveguide resonators using interface engineering Archan Banerjee, Mohammed Alghadeer, Ahemd Hajir, John Mark Kreikebaum, Frank Ogletree, Virginia Altoe, Saleem Rao, Irfan Siddiqi Superconducting resonators are a key component in quantum circuits. While extensive research has explored techniques to improve the quality factor of such devices, the precise structure of amorphous dielectric layers on surfaces and interfaces and their associated loss mechanism remains a topic of active discussion. In this study, we explore the characterization and the fabrication of niobium coplanar waveguide resonators with more than 106 internal quality factor at single-photon-excitation power (measured at 100 mK) for a variety of different surface treatments. Following electrical measurements, resonator samples have been probed using a suite of structural characterization tools (XPS, TEM and AFM) in order to correlate the efficacy of surface treatment with resonator quality factor. We also compare our measurement results with numerical simulations. |
Tuesday, March 3, 2020 10:36AM - 10:48AM |
F16.00012: Reliable Growth of TaN Superconducting Film with Atomic Layer Deposition for Quantum Circuit Applications Wonho Song, Sungchul Jung, Junhyung Kim, Gahyun Choi, Joonyoung Lee, Yonuk Chong, Kibog Park Atomic layer deposition (ALD) is a well-known method to grow a thin film which can ensure the uniformity and conformality of the grown film. In this work, several different thicknesses of TaN thin films are grown on SiO2/Si or Si substrates with plasma enhanced ALD process using the Tris(diethylamido)(tert-butylimido)tantalum(TBTDET) precursor reacted with H2 gas. The grown TaN films show superconductivity reproducibly and their transition temperatures vary in the range of 3-5 K depending on the film thickness. The superconducting transition temperature and microwave transmission properties of TaN films will be analyzed in terms of their correlation with DC transport parameters including carrier type, carrier density, and carrier mobility obtained from Hall effect measurements. |
Tuesday, March 3, 2020 10:48AM - 11:00AM |
F16.00013: Microwave Loss in High-Q Titanium Nitride Resonators Rui Zhang, Ashish Alexander, Christopher Richardson, Frederick C Wellstood, Benjamin Palmer We have measured the loss in a superconducting thin film titanium nitride microwave resonator from 20 mK to 1 K and at different stored microwave powers. The titanium nitride film had a superconducting transition temperature of Tc = 5.5 K and was grown in an MBE by reactively reacting evaporated titanium in a nitrogen plasma. The measured internal loss of the resonator is found to decrease by approximately a factor of 10 from Q-1 = 2.5 x 10-6 at low applied microwave powers and low temperatures to Q-1 = 2.5 x 10-7 at large applied powers and a temperature of 600 mK. We compare the measured Q data to a model based on loss from the interaction of the superconducting resonator with lossy two-level systems and separately to a model we have developed based on non-equilibrium quasiparticles accumulating in regions of the TiNx film with a lower superconducting gap (D). To distinguish between these competing models, we will also discuss results where we apply superconducting pair-breaking infrared light directly to the resonator device and measure the loss. |
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