Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session X16: Superconducting Qubits: 3D Integration and Cryogenic Packaging |
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Sponsoring Units: DQI Chair: Josh Mutus, Google Inc. Room: 201 |
Friday, March 6, 2020 11:15AM - 11:27AM |
X16.00001: Scalable packaging for superconducting qubits with vertical wiring Shuhei Tamate, Yutaka Tabuchi, Laszlo Szikszai, Koichi Kusuyama, Kun Zuo, Yuji Hishida, Wei Qiu, Hirotaka Terai, Masahiro Ukibe, Go Fujii, Kazumasa Makise, Naoya Watanabe, Katsuya Kikuchi, Yasunobu Nakamura Superconducting quantum circuits are one of the most promising platforms for realizing a large-scale quantum computer. To implement realistic quantum error correction codes, such as surface codes, we aim at integrating a two-dimensional array of superconducting qubits in a scalable way. Therefore, a natural strategy for the chip packaging is to use the third dimension for the wiring. Here we demonstrate a packaging scheme for a qubit chip, where coaxial cables for the control and readout of qubits are vertically connected to the backside of the chip. The electrical contacts between the superconducting circuits and coaxial cables are provided by spring probes and superconducting through-silicon via. We will present the design and performance of the chip and package. |
Friday, March 6, 2020 11:27AM - 11:39AM |
X16.00002: Multilayer Microwave Integrated Quantum Circuits: Part 1 Chan U Lei, Lev Krayzman, Suhas Ganjam, Luigi Frunzio, Robert Schoelkopf Superconducting quantum circuits provide a promising platform for quantum information processing. Resonant modes found in superconducting enclosures can be engineered to offer superior coherence and a better electromagnetic environment than their planar analogs. Here, we will discuss the Multilayer Microwave Integrated Quantum Circuit (MMIQC). This platform combines the high coherence of 3D superconducting enclosures with the lithographic precision and versatility of existing MMIC (Monolithic Microwave Integrated Circuit) technology to realize quantum modules that are both scalable and highly coherent. In this talk, we will present an overview of the MMIQC architecture and the ability to realize modular quantum networks. |
Friday, March 6, 2020 11:39AM - 11:51AM |
X16.00003: Multilayer Microwave Integrated Quantum Circuits: Part 2 Lev Krayzman, Chan U Lei, Suhas Ganjam, Luigi Frunzio, Robert Schoelkopf Superconducting quantum circuits provide a promising platform for quantum information processing. Resonant modes found in superconducting enclosures can be engineered to offer superior coherence and a better electromagnetic environment than their planar analogues. Here, we will discuss the Multilayer Microwave Integrated Quantum Circuit (MMIQC). A crucial component of the MMIQC is the realization of a high quality superconducting enclosure. The ability to make such a component necessitates the production of a high quality superconducting seam. In this talk, we will present an indium bump-bonding approach to produce superconducting seams with RF conductance exceeding 10^10/Ωm. |
Friday, March 6, 2020 11:51AM - 12:03PM |
X16.00004: Multilayer Microwave Integrated Quantum Circuits: Part 3 Suhas Ganjam, Chan U Lei, Lev Krayzman, Luigi Frunzio, Robert Schoelkopf Superconducting quantum circuits provide a promising platform for quantum information processing. Resonant modes found in superconducting enclosures can be engineered to offer superior coherence and a better electromagnetic environment than their planar analogs. Here, we will discuss the Multilayer Microwave Integrated Quantum Circuit (MMIQC). A crucial component of the MMIQC is the realization of a high quality superconducting enclosure. In this talk, we will demonstrate on-chip microwave resonant cavities with low-power quality factors exceeding 300 million. In addition, we will describe their power and temperature dependence. Finally, we will discuss factors that may limit the performance of these cavities by placing bounds on intrinsic loss mechanisms. |
Friday, March 6, 2020 12:03PM - 12:15PM |
X16.00005: Principles of Microwave Package Design for Superconducting Quantum Processors Sihao Huang, Benjamin Lienhard, Bharath Kannan, Jochen Braumüller, David K Kim, Joel Wang, Alexander Melville, Bethany Niedzielski, Jonilyn Yoder, Terry Philip Orlando, Simon Gustavsson, William Oliver Superconducting qubits are amongst the most promising platforms towards building near term, practical quantum information processors. As the number of qubits per device increases, package design becomes an increasingly important aspect enabling efficient qubit control. Multiple, often interrelated factors such as spurious modes, conduction losses, and crosstalk impose challenges that require a comprehensive approach to package design. Here, we provide an overview of our recent work aimed at addressing these challenges, including chip-to-board interconnect design, interposer design, and material choices. We present results from simulations of these elements and corresponding physical measurements on a newly designed package. |
Friday, March 6, 2020 12:15PM - 12:27PM |
X16.00006: 3D Integration with Protected Qubits Anjali Premkumar, Andras Gyenis, Pranav Mundada, Andrew Houck Large-scale quantum computation will require 3D integrated architectures to achieve all-to-all connectivity, individual qubit addressability, and protection against crosstalk and decoherence channels. A central challenge in 3D quantum hardware is ensuring that additional materials and structures (such as dielectrics) do not suppress qubit lifetimes. Thus far, 3D integration schemes have typically involved a vacuum region between the qubit and other structures to avoid dielectric loss [1,2,3]. In this talk, we propose to use intrinsically protected qubits for 3D integration: resistance to dielectric loss allows for simple layered structures similar to classical 3D architectures. We show that disjoint support in fluxonium qubits leads to relaxation times ~10ms, even when low-quality-factor SiN is deposited on top. We demonstrate a two-layer fluxonium device fabricated with techniques common in single-layer processing. The ideas explored here will allow for simple, repeatable fabrication processes for 3D quantum processors based on protected qubits. |
Friday, March 6, 2020 12:27PM - 12:39PM |
X16.00007: Quantifying the impact of a caps and vias architecture for superconducting qubits Keith Jackson, Andrew Bestwick, Shane A Caldwell, Matthew J Reagor Scaling high-fidelity superconducting quantum processors to hundreds of qubits requires low on-chip crosstalk at both DC and microwave frequencies, control of the microwave environment seen by each qubit, and accurate coupling strengths between specific modes. To enable this, we describe a chip architecture that combines superconducting caps with recessed cavities bump bonded to a quantum IC with superconducting vias. We describe measurements showing the impact of both caps and vias across a 16+ qubits, including data that enable us to separate out the effects of caps, vias, and the placement of the cap indium bumps on device crosstalk. |
Friday, March 6, 2020 12:39PM - 12:51PM |
X16.00008: Design Considerations for Near-term Quantum Processors Anna Stockklauser Progress in the development of quantum computing systems based on superconducting qubits brings more and more near-term applications within reach. Accelerating this progress requires improvements in the reliability and manufacturability of quantum chips and other specialized components as quantum processors approach 100+ qubits. This talk will address challenges and solutions in the design and fabrication of superconducting qubit-based quantum processors related to scaling, 3D integration, and device operation. We will discuss how these improvements support progress towards demonstrating practical near-term applications with variational algorithms on hybrid quantum-classical machines. |
Friday, March 6, 2020 12:51PM - 1:03PM |
X16.00009: Cryogenic Thermalization Measurements of Microwave Attenuators Aniket Maiti, Vijay Jain, Luigi Frunzio, Robert Schoelkopf Dephasing due to residual thermal photons in readout cavities is a leading factor in limiting the coherence of superconducting qubits. This thermal noise originates from strong cavity drives and poor thermalization of microwave attenuators. It has been shown that cold attenuators could allow one to approach the qubit decoherence limits imposed by T1 [1]. We thus study the thermalization of cryo-attenuators by using a coaxial stub cavity over-coupled to a microwave input line for absolute temperature measurement. In particular, we look at the power dependence and the time constant for the temperature of a few attenuator designs, and discuss strategies for improvement. |
Friday, March 6, 2020 1:03PM - 1:15PM |
X16.00010: Dilution-equivalent solid-state chip refrigeration Alberto Ronzani, Janne Lehtinen, Emma Mykkanen, Antti Kemppinen, Leif Grönberg, Antti Manninen, Mika Prunnila Cooling below 100 mK is an operative prerequisite in several quantum technology applications. It is typically achieved in expensive He3/He4 dilution refrigerators, where massive thermal payloads are cooled to very low temperatures over the course of tens of hours. Yet, in several quantum devices, only few miniaturized active elements are required to reach such low temperature levels. |
Friday, March 6, 2020 1:15PM - 1:27PM |
X16.00011: Hot electron measurements below 100 mK for quantum devices Zachary Steffen, Sudeep Dutta, Rui Zhang, Yizhou Huang, Kungang Li, Frederick C Wellstood, Benjamin Palmer Recently, the electron-phonon coupling constant of the resistive alloy material nichrome (NiCr) was estimated as ΣNiCr = (5 x 108) Wm-3K-5 from measurements of the dephasing rate of a superconducting transmon qubit coupled to a NiCr attenuator [1]. In this talk, we will discuss ongoing measurements to more directly measure the electron temperature and find the electron-phonon coupling constant of NiCr. In particular, we have fabricated NIS junctions consisting of NiCr/AlOx/Al structures and measured the current voltage characteristics at temperatures down to 20 mK. These measurements will be used to extract the electron temperature of the NiCr material which can be compared to the previously reported value, allowing for more accurate thermal modeling of future NiCr devices. |
Friday, March 6, 2020 1:27PM - 1:39PM |
X16.00012: Extending Superconducting Qubits Out of Plane (Part 1): Qubits with Air Bridge Crossovers in Multi-Tier Stacks Jonilyn Yoder, Justin Mallek, David K Kim, Donna-Ruth Yost, Greg Calusine, Rabindra Das, Alexandra Day, Alexander Melville, Bethany M Niedzielski, Danna Rosenberg, Gabriel Orr Samach, Mollie Schwartz, Steven Weber, William Oliver Out-of-plane connectivity within superconducting quantum circuits enables increased complexity and wiring density. We are developing heterogeneous 3D integration of a qubit tier combined with an interposer with high-aspect-ratio superconducting through-silicon vias and a superconducting multi-chip module. In part 1 of this talk, we will focus on circuit complexity within the superconducting qubit tier, including implementation of air bridge crossovers (1) to increase mutual inductance by directly embedding them within qubit and coupler loops, (2) to improve connectivity of the ground plane, and (3) as a method for routing wires and circuit elements past each other. |
Friday, March 6, 2020 1:39PM - 1:51PM |
X16.00013: Extending Superconducting Qubits Out of Plane (Part 2): Through-Silicon Vias Justin Mallek, Jonilyn Yoder, Donna-Ruth Yost, Rabindra Das, Alexandra Day, Danna Rosenberg, Greg Calusine, Matthew Cook, Evan Golden, David K Kim, Alexander Melville, Bethany Niedzielski, Mollie Schwartz, Corey Stull, Sergey Tolpygo, Wayne Woods, William Oliver Addressing complex arrays of high coherence qubits is a necessary capability for the construction of a quantum processor. To enable high connectivity of superconducting qubits we are utilizing heterogeneous 3D integration of a qubit tier, an interposer with high-aspect-ratio superconducting through-silicon vias (TSVs), and a superconducting multi-chip module. In part 2 of this talk we will focus on the fabrication of TSVs within the interposer tier and their implementation within multi-tier stacks. |
Friday, March 6, 2020 1:51PM - 2:03PM |
X16.00014: Quantifying Losses in Transmon Qubits Greg Calusine, Wayne Woods, Alexander Melville, Kyle Serniak, David K Kim, Jonilyn Yoder, William Oliver Reducing losses in superconducting qubit circuits is critical for enabling the development of large-scale quantum computing architectures. This task is especially challenging in the face of variability resulting from device-to-device differences and fluctuating device properties. We apply statistical characterization of sets of superconducting resonators and transmon qubits to overcome variability and quantify loss contributions from a variety of sources such as surface and bulk dielectrics, packaging, and nonequilibrium quasiparticles. As part of this approach, we develop the fabrication processes and EM modeling techniques necessary for accurately modeling dielectric losses. Through this study, we seek to develop a model of qubit losses that allows for iterative improvement in device coherences and consistency. |
Friday, March 6, 2020 2:03PM - 2:15PM |
X16.00015: Effects of surface treatments and packaging on transmon qubits Matthias Mergenthaler, Clemens Müller, Marc Ganzhorn, Stephan Paredes, Peter Müller, Stefan Filipp, Andreas Fuhrer The last two decades have seen significant advances in the coherence times of superconducting qubits. However, further progress in transmon coherence times seems to require substantial effort in understanding the remaining limitations due to material interfaces and imperfections, which give rise to two level fluctuators [1-3]. Often, ion milling is an integral part of Josephson junction fabrication and possibly damages the material surface, but its impact on qubit coherence is not well understood and needs experimental investigation. |
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