Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V35: Materials and Fabrication for Superconducting QubitsFocus
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Sponsoring Units: DQI Chair: Martin Sandberg, IBM Thomas J. Watson Research Center Room: BCEC 205B |
Thursday, March 7, 2019 2:30PM - 2:42PM |
V35.00001: A New Technique to Measure Microwave Dielectric Material Loss Kaicheng Li, Christopher J Axline, Luke Burkhart, Benjamin Chapman, Chan U Lei, Vijay Jain, Lev Krayzman, Philip Reinhold, Luigi Frunzio, Robert J Schoelkopf Qubit coherence time is essential in quantum computation, since, in tandem with gate speed, it governs the number of coherent operations one can eventually perform on a quantum computer. In the field of circuit quantum electrodynamics, a qubit is often formed by the non-linearity of a Josephson junction fabricated on a dielectric substrate. Therefore, any dielectric loss in the substrate can be an important contribution to qubit coherence. Indeed, recent studies suggest that among different qubit loss channels dielectric loss may be a substantial one. In this talk, we describe a sensitive method to selectively measure microwave dielectric substrate loss and present preliminary measurements with the technique. |
Thursday, March 7, 2019 2:42PM - 2:54PM |
V35.00002: Atomic defects in silicon compared with standard two-level defects Liuqi Yu, Y. J. Rosen, Kevin Daniel Osborn Atomic two-level systems (TLSs) in materials affect the performance of superconducting quantum devices and new fundamental studies are needed to better understand them. It was found1,2 that the TLS bath, initially saturated by the microwave field excitations, can undergo adiabatic transitions when an additional sweeping fields is applied. Although more TLSs would remain in the ground state, the overall rate of TLSs absorbing the microwave field, increases as the sweep rate is increased due to the increase in TLS crossings in the standard distribution. It leads to a universal plataeu in non-equilibrium loss equal to the intrinsic linear dielectric loss at the low power limit. Here, we extend the measurements by using a new dielectric which is important in light of qubit substrates and semiconductor qubit devices: amorphous silicon. Quite surprisingly, the loss tangent reveals a second increases in loss with increasing bias rate. The data will be compared to previous data which fit the standard TLS model. We plan to verify the phenomenon with further studies. |
Thursday, March 7, 2019 2:54PM - 3:06PM |
V35.00003: Atomic Layer Deposition of Titanium Nitride for Quantum Circuits Abigail Shearrow, Gerwin Koolstra, Samuel Whiteley, Nathan D Earnest, Peter Barry, Joseph Heremans, David Awschalom, Erik Shirokoff, David Schuster High kinetic inductance thin films are of great interest for superconducting detectors, coupling to hybrid systems, and novel superconducting qubits. We demonstrate that titanium nitride thin films grown via plasma-enhanced atomic layer deposition support superconducting microwave resonators with internal quality factors up to 1.0 million at single photon powers, and find that the dominant loss mechanism in these resonators is likely due to two-level systems. Utilizing nanowire geometries, we realize characteristic impedances greater than a resistance quantum with Z ~ 28 kΩ while maintaining low losses and a compact device footprint (8×8 μm2). The corresponding increase in zero point voltage fluctuations makes this material an excellent candidate for integration into hybrid quantum systems and quantum sensing. |
Thursday, March 7, 2019 3:06PM - 3:18PM |
V35.00004: Fabrication of Sn-Cu alloy superconducting films for filled superconducting through-silicon vias Go Fujii, Masahiro Ukibe, Kazumasa Makise, Mutsuo Hidaka, Shuichi Nagasawa, Hirotake Yamamori, Kunihiro Inomata, Takahiro Yamada, Shiro Kawabata Quantum annealing (QA) is one of quantum computers to solve combinatorial optimization and sampling problems. We have developed new three-dimensional (3D) packaging structure, which obtain a scalability and a flexibility in the circuit size to realize customized circuits for solved problems by stacking qubit-chip, interposer, and package-substrate as much as necessary. In the 3D packaging, superconducting TSVs are necessary because generating heat in through-silicon vias (TSVs) used to connect the qubit and the package-substrate is a big problem. So far, we have fabricated superconducting TSVs with pure Sn, however, fabrication yield of the TSVs was low because it was difficult to fill the Sn in deep holes by electroplating process (EP). In this work, we have changed the material from the Sn to Sn-Cu alloy to solve the above problem. A Sn9-Cu alloy film fabricated by the EP exhibited transition temperature (Tc) of 2.4 K. Although the Tc of the Sn9-Cu alloy is about 30 % lower than that of the pure Sn, it is sufficient for our QA machine system. |
Thursday, March 7, 2019 3:18PM - 3:30PM |
V35.00005: Fabrication of superconducting qubits using free-standing mineral masks Ioannis Tsioutsios, Kyle Serniak, Zhixin Wang, Shyam Shankar, Luigi Frunzio, Robert Schoelkopf, Michel H. Devoret Over the last years there has been a significant improvement on the energy relaxation properties of superconducting qubits. State-of-the-art transmon and fluxonium qubits exhibit energy relaxation times in the order of hundreds of microseconds and few milliseconds respectively. Progress in their design has resulted in minimizing losses coming from the dielectric environment and radiation into the electromagnetic environment, in addition to gains due to better understanding and control of their inductive losses. However, advancements on reducing dielectric losses associated with organic residues produced by traditional fabrication techniques have been modest. In this talk, we will propose a new fabrication technology for planar superconducting circuits that replaces the commonly used resist-based lithography masks with free-standing mineral masks. Furthermore, we will present preliminary results on the energy relaxation properties and reproducibility of transmon qubits that are fabricated using this new method. |
Thursday, March 7, 2019 3:30PM - 3:42PM |
V35.00006: MBE grown AlN-TiN heterostructures for superconducting quantum circuits Christopher Richardson, Ashish Alexander, Christopher Weddle Superconducting transition metal nitrides are a family of superconductors that have been used to produce high internal quality factor superconducting coplanar waveguide (CPW) resonators. Plasma assisted molecular beam epitaxy (MBE) is used to grow both superconducting nitrides and wide-bandgap nitride bilayer heterostructures. This combination of nitride materials provides sufficient degrees of freedom that synthesis of an epitaxial Josephson junction may be possible. Here early stages of this approach are evaluated through measurement of the single photon loss of aluminum nitride that is explored as both an overlayer and underlayer of TiN superconducting CPW resonators. |
Thursday, March 7, 2019 3:42PM - 3:54PM |
V35.00007: WITHDRAWN ABSTRACT
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Thursday, March 7, 2019 3:54PM - 4:06PM |
V35.00008: Microwave loss in amorphous silicon for coherent superconducting technologies William Koehl, Stanley F Steers, Moe Khalil, Jon Cochran, Daniel Robert Queen, Justin Hackley, Khyhouth Lim, Jim Kelliher, Austin Doyle, Patrick Warner, Monica Lilly, Micah Stoutimore Efforts to design superconducting quantum technologies have generated an interest in understanding the materials mechanisms responsible for microwave photon loss in coherent devices. While a desire for long coherence times has driven many groups to pursue devices fabricated on crystalline substrates, close study of loss in deposited dielectrics has also played an important role in the development of the field. Recent efforts at 3D integration suggest that a more complete understanding of the relationship between loss and defectivity in amorphous films is still needed. We discuss current microstructural models of defectivity in amorphous silicon (a-Si), a material commonly used in the semiconductor and solar industries, and relate these concepts to microwave photon loss in superconducting resonators fabricated on a-Si films deposited under growth conditions targeting low defect incorporation. Experimental data from cryogenic quality factor measurements will be presented and coupled to structural information derived via TEM and other materials spectroscopies. |
Thursday, March 7, 2019 4:06PM - 4:18PM |
V35.00009: Optical Direct-Write Lithography of Shadow Mask Josephson Junctions Jonathan Monroe, Kater Murch We have developed a technique to fabricate Josephson junctions with a direct-write laser lithography system, enabling fast writing of large-area patterns. Using standard Niemeyer-Dolan bridge shadow deposition techniques, we create relatively large junctions (0.5 um^2) suitable for array-based parametric amplifiers. We explore fabrication techniques to create low critical current junctions for superconducting qubits. We present results on reproducibility and performance of Josephson parametric amplifiers and transmon qubits utilizing these junctions. |
Thursday, March 7, 2019 4:18PM - 4:30PM |
V35.00010: Surface Loss Characterization and Comparison in Aluminum, Niobium, and Titanium Nitride Superconducting Resonators Alexander Melville, Greg Calusine, Wayne Woods, Evan Golden, Jovi Miloshi, Arjan Sevi, Jonilyn L Yoder, William D Oliver Uniquely characterizing loss from two-level systems (TLS) at metal-substrate, metal-air, and substrate-air interfaces and in a dielectric substrate is challenging due to the nearly proportional scaling of the dielectric participations in response to changes in geometry and anisotropic trench depth. We developed a technique utilizing isotropic etching to assign a specific loss tangent to each dielectric, and use that to determine the dominant dielectric losses for a specific fabrication process, enabling targeted geometry and process changes to maximize performance. In this talk, we characterize the loss from high quality factor resonators (Qi>1M) for aluminum, titanium nitride, and niobium, and demonstrate the technique’s application by targeting specific defect layers to alter the dielectric losses specifically from these defect layers. |
Thursday, March 7, 2019 4:30PM - 4:42PM |
V35.00011: Study of atomic two-level defects within a Josephson junction proxy Chih-Chiao Hung, Neda Forouzani, Kevin Daniel Osborn In superconducting qubits, thermally grown aluminum oxide is generally used as the barrier between two superconducting electrodes to form the S-I-S Josephson junction (JJ). This oxide is amorphous and is known to contain random, atomic-sized two-level systems (TLSs) which are a source of decoherence in superconducting qubits. Here, we present a study of TLSs in parallel plate capacitors mimicking a JJ (Al/AlOx/Al), but where the dielectric layer is 20 nm and therefore block the tunneling supercurrent. In this JJ proxy, the defects near the in AlOx and near the interface ofAl/AlOx can be studies using a new analysis method only demonstrated before with a different dielectric. Using a resonator device with a four-arm bridge capacitor, one can tune the frequency of TLSs by applying a DC electric field, and observe individual TLSs reach degeneracy with the resonator in a demonstration of cavity QED with TLS. The transmission versus applied electric field would give us the TLS dipole moment’s z-component. We will study these resonators in an effort to better understand TLSs within typical JJs. |
Thursday, March 7, 2019 4:42PM - 4:54PM |
V35.00012: Microwave Properties of Exfoliated Hexagonal Boron Nitride Abhinandan Antony, Martin V Gustafsson, Guilhem Ribeill, Mitali Banerjee, Thomas A Ohki, James Hone, Kin Chung Fong Interfacial and bulk dielectric losses in superconducting qubits are some of the key factors limiting device coherence. We investigate the microwave properties of thin flakes of hexagonal boron nitride (h-BN), which have the potential to serve as low-loss elements in superconducting transmon qubits. The flakes, which are exfoliated from high-quality single-crystals to thicknesses of a few tens of nanometers, have atomically flat interfaces and low defect densities. Our process allows them to be coated with superconducting layers on both sides, thus forming parallel-plate capacitors. By embedding these capacitors in superconducting microwave resonators, we can determine the dielectric constant and loss tangent of h-BN under conditions relevant for qubit operation. Apart from the promise of improved coherence, the parallel-plate geometry would enable qubits to be designed with drastically reduced footprints and cross-talk compared to planar devices. |
Thursday, March 7, 2019 4:54PM - 5:30PM |
V35.00013: Operating a Quantum Processor with Material Defects Invited Speaker: Paul Klimov A challenge in operating a quantum processor is mitigating computational errors from material two-level-system defects. Defects cause qubit-performance metrics to fluctuate in frequency, time, and between nominally identical qubits [1]. In frequency-tunable qubit architectures, it is possible to mitigate defect-related performance fluctuations in-situ by judiciously picking qubit operating frequencies. The defect avoidance problem thus maps to an optimization problem with a high-dimensional, non-convex, and time-dependent objective whose parameters are defined by defects’ physical properties. In this talk, I will discuss recent research towards understanding defect properties, the defect avoidance problem, and related benchmarks. |
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