Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session Y46: Superconducting Circuits: Fabrication Advances & Measurements |
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Sponsoring Units: GQI Chair: Jonilyn Yoder, MIT Lincoln Laboratory Room: 393 |
Friday, March 17, 2017 11:15AM - 11:27AM |
Y46.00001: Characterization of shadow evaporated Al/AlOx/Al Josephson Junctions Brian Burkett, Z. Chen, B. Chiaro, A. Dunsworth, B. Foxen, C. Neill, C. Quintana, J. Wenner, John. M. Martinis Building a large-scale quantum computer depends crucially on developing a Josephson junction fabrication process that is reliable. We have collected and analyzed data for more than $10^5$ junctions, measured using an automated DC probe station at room temperature. Using this method, we can identify and monitor the impact of subtle process parameters on junction performance resulting from aging, pressure, lithography and surface treatment. We also present transmission electron microscopy and electron energy loss spectroscopy of our junctions. [Preview Abstract] |
Friday, March 17, 2017 11:27AM - 11:39AM |
Y46.00002: Variability metrics in Josephson Junction fabrication for Quantum Computing circuits Sami Rosenblatt, Jared Hertzberg, Markus Brink, Jerry Chow, Jay Gambetta, Zhaoqi Leng, Andrew Houck, J.J. Nelson, Britton Plourde, Xian Wu, Russell Lake, Jeff Shainline, David Pappas, Umeshkumar Patel, Robert McDermott Multi-qubit gates depend on the relative frequencies of the qubits. To reliably build multi-qubit devices therefore requires careful fabrication of Josephson junctions in order to precisely set their critical currents. The Ambegaokar-Baratoff relation between tunnel conductance and critical current implies a correlation between qubit frequency spread and tunnel junction resistance spread. Here we discuss measurement of large numbers of tunnel junctions to assess these resistance spreads, which can exceed 5{\%} of mean resistance. With the goal of minimizing these spreads, we investigate process parameters such as lithographic junction area, evaporation and masking scheme, oxidation conditions, and substrate choice, as well as test environment, design and setup. In addition, trends of junction resistance with temperature are compared with theoretical models for further insights into process and test variability. [Preview Abstract] |
Friday, March 17, 2017 11:39AM - 11:51AM |
Y46.00003: Fabrication of Josephson Junction without shadow evaporation Xian Wu, Hsiangsheng Ku, Junling Long, David Pappas We developed a new method of fabricating Josephson Junction (Al/AlO$_{\mathrm{X}}$/Al) without shadow evaporation. Statistics from room temperature junction resistance and measurement of qubits are presented. Unlike the traditional ``Dolan Bridge'' technique, this method requires two individual lithographies and straight evaporations of Al. Argon RF plasma is used to remove native AlO$_{\mathrm{X}}$ after the first evaporation, followed by oxidation and second Al evaporation. Junction resistance measured at room temperature shows linear dependence on $P_{ox} $ (oxidation pressure), $\sqrt {t_{ox} } $ (oxidation time), and inverse proportional to junction area. We have seen 100{\%} yield of qubits made with this method. This method is promising because it eliminates angle dependence during Junction fabrication, facilitates large scale qubits fabrication. [Preview Abstract] |
Friday, March 17, 2017 11:51AM - 12:03PM |
Y46.00004: Fabrication of Circuit QED Quantum Processors, Part 1: Extensible Footprint for a Superconducting Surface Code A. Bruno, D.J. Michalak, S. Poletto, J.S. Clarke, L. DiCarlo Large-scale quantum computation hinges on the ability to preserve and process quantum information with higher fidelity by increasing redundancy in a quantum error correction code. We present the realization of a scalable footprint for superconducting surface code based on planar circuit QED. We developed a tileable unit cell for surface code with all I/O routed vertically by means of superconducting through-silicon vias (TSVs). We address some of the challenges encountered during the fabrication and assembly of these chips, such as the quality of etch of the TSV, the uniformity of the ALD TiN coating conformal to the TSV, and the reliability of superconducting indium contact between the chips and PCB. We compare measured performance to a detailed list of specifications required for the realization of quantum fault tolerance. Our demonstration using centimeter-scale chips can accommodate the \textasciitilde 50 qubits needed to target the experimental demonstration of small-distance logical qubits. [Preview Abstract] |
Friday, March 17, 2017 12:03PM - 12:15PM |
Y46.00005: Fabrication of Circuit QED Quantum Processors, Part 2: Advanced Semiconductor Manufacturing Perspectives D.J. Michalak, A. Bruno, R. Caudillo, A.A. Elsherbini, J.A. Falcon, Y.S. Nam, S. Poletto, J. Roberts, N.K. Thomas, Z.R. Yoscovits, L. DiCarlo, J.S. Clarke Experimental quantum computing is rapidly approaching the integration of sufficient numbers of quantum bits for interesting applications, but many challenges still remain. These challenges include: realization of an extensible design for large array scale up, sufficient material process control, and discovery of integration schemes compatible with industrial 300 mm fabrication. We present recent developments in extensible circuits with vertical delivery. Toward the goal of developing a high-volume manufacturing process, we will present recent results on a new Josephson junction process that is compatible with current tooling. We will then present the improvements in NbTiN material uniformity that typical 300 mm fabrication tooling can provide. While initial results on few-qubit systems are encouraging, advanced processing control is expected to deliver the improvements in qubit uniformity, coherence time, and control required for larger systems. [Preview Abstract] |
Friday, March 17, 2017 12:15PM - 12:27PM |
Y46.00006: Superconducting high kinetic inductance resonators made from granular aluminum L. Gruenhaupt, S. T. Skacel, N. Maleeva, Z. Wang, A. V. Ustinov, H. Rotzinger, I. M. Pop We present experimental results on superconducting thin film resonators fabricated from granular aluminum. By employing an electron beam evaporation process that allows an in-situ integration with Josephson junctions, we fabricated high kinetic inductance resonators with the goal of measuring their internal dissipation and non-linearity. Our results are in agreement with a theoretically predicted kinetic inductance in the range of $1\,\rm{nH}$ per square. Measurements in the single photon regime show internal quality factors in excess of $10^5$ and self-Kerr coefficients in the range of $10 - 100\,\rm{Hz}$ per photon. \\ The obtained results are promising for applications in high characteristic impedance superconducting circuits for quantum information processing as well as for kinetic inductance detectors. [Preview Abstract] |
Friday, March 17, 2017 12:27PM - 12:39PM |
Y46.00007: Supercritical Fluid-Assisted Processing of Superconducting Al Resonators Christopher Barrett, Cynthia Warner, Bruce Arey, Shutthanandan Vaithiyalingam, Marvin Warner, Nathan Siwak, Christopher Richardson Microfabrication-induced processing artifacts have been shown to limit the coherence times of both planar and 3D superconducting qubits. Energy loss in these devices can arise as a result of interactions with two-level system defects, which are being correlated to thin layers of lossy material and/or nano-sized particulate. To this end, we present recent results from a number of different conventional and non-conventional techniques used in locating and characterizing these sources of loss on coplanar waveguide resonators. Using these observations as a metric, a novel system for supercritical fluid-assisted cleaning of superconducting aluminum features will be discussed at length. Supercritical CO$_{\mathrm{2}}$ can serve as an effective solvent system to assist in the delivery of various co-solvents or stripping agents to even the smallest patterned features, with minimal impact to the aluminum layer. The adoption of less-invasive forms of device processing should mitigate artifact formation, translating into substantially improved coherence times. [Preview Abstract] |
Friday, March 17, 2017 12:39PM - 12:51PM |
Y46.00008: Characterization of superinductors fabricated by a reactive evaporation of TiN Raymond Mencia, Yen-Hsiang Lin, Vladimir Manucharyan A superinductance is a circuit element whose broadband microwave impedance reaches the scale of resistance quantum h/4e\textasciicircum 2 \textasciitilde 6.5kOhm. Here we report an approach of fabricating such circuit elements by a reactive e-beam evaporation of TiN. We use deposition pressure and film thickness to tune TiN film close to a superconductor-insulator transition. Our films have kinetic inductance orders of magnitude higher than the geometric one with the critical temperature being above \textasciitilde 2K. Material analysis revealed that the enhanced kinetic inductance is linked to oxygen incorporation. We present DC and microwave characterization of TiN fabricated using our new method combined with a lift-off process. [Preview Abstract] |
Friday, March 17, 2017 12:51PM - 1:03PM |
Y46.00009: Microfabrication of low-loss lumped-element Josephson circuits for non-reciprocal and parametric devices Katarina Cicak, Florent Lecocq, Leonardo Ranzani, Gabriel A. Peterson, Shlomi Kotler, John D. Teufel, Raymond W. Simmonds, Jose Aumentado Recent developments in coupled mode theory have opened the doors to new nonreciprocal amplification techniques that can be directly leveraged to produce high quantum efficiency in current measurements in microwave quantum information. However, taking advantage of these techniques requires flexible multi-mode circuit designs comprised of low-loss materials that can be implemented using common fabrication techniques. In this talk we discuss the design and fabrication of a new class of multi-pole lumped-element superconducting parametric amplifiers based on Nb/Al-AlOx/Nb Josephson junctions on silicon or sapphire. To reduce intrinsic loss in these circuits we utilize PECVD amorphous silicon as a low-loss dielectric ($\tan \delta \sim 5 \times 10^{-4}$), resulting in nearly quantum-limited directional amplification. [Preview Abstract] |
Friday, March 17, 2017 1:03PM - 1:15PM |
Y46.00010: A coaxial circuit QED architecture for quantum computing Joseph Rahamim, Tanja Behrle, Michael Peterer, Andrew Patterson, Peter Spring, Riccardo Manenti, Giovanna Tancredi, Peter Leek A major obstacle in scaling up superconducting circuit architectures for quantum computing is the difficulty of having the many required control and measurement lines on the same chip as the qubits. As a solution, we present a coaxial circuit QED architecture in which a qubit and lumped element LC resonator are fabricated on opposing sides of a single chip, and control and readout are provided by coaxial wiring running perpendicular to the chip plane. We present spectroscopic and time-resolved measurements of a fabricated device, demonstrating excellent agreement with circuit QED in the dispersive regime. The architecture allows for scaling via nearest-neighbour coupling to large arrays of selectively controlled and measured qubits, with a straight-forward fabrication procedure and without the complexity of in-plane wiring. [Preview Abstract] |
Friday, March 17, 2017 1:15PM - 1:27PM |
Y46.00011: Superconducting qubits on silicon substrates for quantum device integration Andrew Keller, Michael Fang, Paul Dieterle, Brett Berger, Oskar Painter We present a process for fabricating low-loss superconducting transmon qubits, using aluminum metallization on silicon and silicon-on-insulator substrates. The buried oxide in silicon-on-insulator substrates can be undercut by an HF vapor process compatible with the patterned aluminum features, in principle permitting optical waveguides and mechanical resonators to reside on the same chip as the qubits. We have characterized our qubits by pulsed time-domain measurements and find qubit lifetimes and coherence times comparable to those attainable on sapphire substrates. This suggests a route towards integrating qubits with quantum coherent microwave-to-optical transducers for quantum networking applications. [Preview Abstract] |
Friday, March 17, 2017 1:27PM - 1:39PM |
Y46.00012: Additive Manufactured Superconducting Cavities Eric Holland, Yaniv Rosen, Nathan Woolleet, Nicholas Materise, Thomas Voisin, Morris Wang, Jorge Mireles, Gianpaolo Carosi, Jonathan Dubois Superconducting radio frequency cavities provide an ultra-low dissipative environment, which has enabled fundamental investigations in quantum mechanics, materials properties, and the search for new particles in and beyond the standard model. However, resonator designs are constrained by limitations in conventional machining techniques. For example, current through a seam is a limiting factor in performance for many waveguide cavities. Development of highly reproducible methods for metallic parts through additive manufacturing, referred to colloquially as “3D printing”, opens the possibility for novel cavity designs which cannot be implemented through conventional methods. We present preliminary investigations of superconducting cavities made through a selective laser melting process, which compacts a granular powder via a high-power laser according to a digitally defined geometry. Initial work suggests that assuming a loss model and numerically optimizing a geometry to minimize dissipation results in modest improvements in device performance. Furthermore, a subset of titanium alloys, particularly, a titanium, aluminum, vanadium alloy (Ti – 6Al - 4V) exhibits properties indicative of a high kinetic inductance material. [Preview Abstract] |
Friday, March 17, 2017 1:39PM - 1:51PM |
Y46.00013: Paramagnetic Spin Dynamics on Different Terminations of Al2O3 Keith Ray, Jonathan Dubois, Vincenzo Lordi Superconducting qubits are susceptible to magnetic flux noise which reduces their coherence through dephasing. The microscopic origins of the observed magnetic flux noise have not been fully characterized. Questions remain as to where the most relevant spins reside that couple to the qubit, the nature of the spin-spin coupling in realistic materials, and the behavior of the resulting spin system dynamics. Paramagnetic O2 has been previously identified experimentally as a likely flux noise source [Phys. Rev. Applied 6, 041001 (2016)] and computational studies [PRL 112, 017001 (2014)] of magnetic spins induced by molecules adsorbed on bare Al-terminated Al2O3 demonstrated the possibility of nearly degenerate adsorbate magnetic states. Here, we present a density functional theory investigation of magnetic noise associated with other Al2O3 surfaces likely to be encountered in experiment. Motivated by noise models involving spin clusters on the surface, we calculate the exchange interaction between adsorbed molecules, OH groups and paramagnetic O2, as well as the magnetic state energy splitting and anisotropy, on fully hydroxylated and Al terminated Al2O3. We use the calculated magnetic quantities to parametrize Monte Carlo models that characterize the spin dynamics, taking into account the disorder of absorbed O2 molecules that define a spin lattice. [Preview Abstract] |
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