Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session S39: Focus Session: Superconducting Qubits: Materials and Characterization |
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Sponsoring Units: GQI Chair: Kevin Osborn, Laboratory for Physicsl Sciences Room: 213AB |
Thursday, March 5, 2015 8:00AM - 8:36AM |
S39.00001: The Roles of Materials, Processing, and Design in Quantum Information Circuits Invited Speaker: David Pappas Significant progress has been made in the coherence of superconducting circuits for resonators and qubits. Over the last decade, the importance of loss and decoherence from defects at interfaces and on surfaces has been recognized and mitigated by optimizing the materials and minimizing their participation in the circuit. This has resulted in novel new designs for quantum circuits, both 3D and 2D circuits. Some or our new designs will be discussed, and these developments will be compared and contrasted to ongoing surface science studies of ion traps that has resulted in improved operations with two orders of magnitude lower heating rates. [Preview Abstract] |
Thursday, March 5, 2015 8:36AM - 8:48AM |
S39.00002: High Quality Factor MBE-grown Aluminum on Silicon Planar Resonators Anthony Megrant, Z. Chen, B. Chiaro, A. Dunsworth, C. Quintana, B. Campbell, R. Barends, Y. Chen, A. Fowler, I.-C. Hoi, E. Jeffrey, J. Kelly, J. Mutus, C. Neill, P.J.J. O'Malley, P. Roushan, D. Sank, A. Vainsencher, J. Wenner, T. White, C. Palmstrom, J.M. Martinis, A.N. Cleland Linear arrays of planer Xmon qubit circuits fabricated using thin aluminum films on sapphire substrates have resulted in long coherence times and high fidelity gates. Scaling up to larger circuits, including two-dimensional qubit arrays, may however benefit from building circuits on silicon instead of sapphire substrates. I will present recent tests in this direction, reporting on measurements of superconducting coplanar waveguide resonators fabricated using aluminum films deposited on silicon in a molecular beam epitaxy (MBE) system. These resonators exhibit exceptional performance, with quality factors at low temperatures and single photon excitation energies exceeding 5x10$^{\mathrm{6}}$. [Preview Abstract] |
Thursday, March 5, 2015 8:48AM - 9:00AM |
S39.00003: Developing TiN resonators with high kinetic inductance Peng Xu, Yaniv Rosen, Aruna Ramanayaka, Bahman Sarabi, Jaim Iftekhar, Kevin Osborn Titanium nitride (TiN) has recently become a material of interest in the superconducting resonator and quantum computing communities due to its high quality factors and high kinetic inductances. By introducing an RF-induced DC voltage bias to the substrate during growth, we have found a reliable method of sputtering superconducting TiN. With optimized bias voltage and thickness, we have fabricated resonators where the kinetic inductance is over ten times greater than the geometric inductance. We report on progress towards increasing this value while maintaining high quality factors. [Preview Abstract] |
Thursday, March 5, 2015 9:00AM - 9:12AM |
S39.00004: Enhancing the coherence of 3D qubits suitable for multi-qubit experiments Baleegh Abdo, Douglas McClure, Hanhee Paik, Martin Sandberg, Jay Gambetta, Oliver Dial Superconducting qubits coupled to 3D cavities [1,2] have several advantages over qubits coupled to planar cavities on the same chip, e.g., 1) they can be individually designed, tested, and integrated, 2) they exhibit better microwave hygiene than their 2D counterpart, and 3) they possess higher coherence times, in part because they have reduced participation ratios for surface dielectric layers that can be lossy. However, in order to implement the surface code using a multi-qubit system, 3D qubits and their corresponding microwave cavities have to meet several competing requirements in addition to preserving long coherence, such as large coupling of the 3D qubit to two adjacent microwave resonators, sufficient coupling to other qubits, and large microwave isolation between different cavities. Finding a qubit design that balances all of these requirements has proved challenging so far. In this work, we apply a combination of simulations and experiments to investigate a variety of loss mechanisms that are particularly relevant for multi-qubit systems. Based on this learning, we identify changes in the design and materials of these systems that can lead to enhancement of their coherence times. [1] H. Paik et al., PRL 107, 240501 (2011) [2] C. Rigetti et al., PRB 86, 100506(R)(2012). [Preview Abstract] |
Thursday, March 5, 2015 9:12AM - 9:24AM |
S39.00005: Integrating superconducting qubit systems for improved quantum operations Stefan Filipp, Sarah Sheldon, Easwar Magesan, Lev S. Bishop, Matthias Steffen, Jerry M. Chow, Jay M. Gambetta Recent progress in the field of superconducting circuits has led to qubit coherence times exceeding by far typical single and two-qubit gate times. In this regime, in which relaxation (T$_1$) and dephasing (T$_2$) times are above 40 and 50 microseconds, respectively, quantum gates are not limited by intrinsic noise sources. We enter this regime by optimizing the design of coplanar transmon qubits to reduce the influence of surface loss. Furthermore, we have eliminated spurious microwave resonances which we can detect by monitoring the qubit coherence while sweeping the frequency of an external microwave drive applied to the system. To improve T$_2$ times, we minimize dephasing caused by thermal photons in coupled resonator modes by increasing the attenuation of the readout drive lines. To maintain the ability to drive fast gates with strong microwave signals while preserving coherence, we employ weakly capacitively coupled control lines providing independent control of the qubits and allowing for improved two-qubit entangling gate operations. [Preview Abstract] |
Thursday, March 5, 2015 9:24AM - 9:36AM |
S39.00006: Improving Superconducting Qubit Lifetimes with Broadband Filters Nicholas Bronn, Antonio Corcoles, Jared Hertzberg, Srikanth Srinivasan, Jerry Chow, Jay Gambetta, Matthias Steffen, Yanbing Liu, Andrew Houck In circuit quantum electrodynamics, the state of the qubit is read out via a resonator at a different frequency than that of the qubit. Spontaneous qubit decay via the resonator may be suppressed by engineering an impedance mismatch at the qubit frequency, while still allowing a large coupling between the resonator and external environment necessary for fast, high fidelity readout. We present a stepped-impedance filter with a large stop-band in the qubit frequency range and demonstrate its effect on qubit lifetime. This filter is also effective when used in an off-chip geometry. [Preview Abstract] |
Thursday, March 5, 2015 9:36AM - 9:48AM |
S39.00007: Strong interaction of a transmon qubit with 1D band-gap medium Yanbing Liu, Darius Sadri, Andrew Houck, Nicholas Bronn, Jerry Chow, Jay Gambetta The spontaneous emission of an atom will be enhanced or suppressed in a structured vacuum, commonly known as Purcell effect. Moreover, in a frequency gap medium, an atom-photon bound state is predicted to exist in the band gap, causing the localization of light. Here using the technology of circuit quantum electrodynamics, we experimentally explore this mechanism by fabricating a microwave step-impedance filter strongly coupled to a transmon qubit. Standard transmission and spectroscopy measurements support the existence of atom-photon bound states in the system. Correlation measurement shows that the atom-photon interaction induces strong correlation of the transmitted light through the system. [Preview Abstract] |
Thursday, March 5, 2015 9:48AM - 10:00AM |
S39.00008: Parallel Loss Channels in Superconducting Epitaxial Aluminum Resonators Christopher Richardson, Nathan Siwak, Lei He Superconducting epitaxial aluminum (epi-Al) on silicon and sapphire has demonstrated low-loss performance that is desirable for linear circuit elements in quantum computing.~ Most often, it is process artifacts that limit the performance of devices fabricated from epi-Al.~ Two common artifacts are photoresist residue that is impossible to observe with optical microscopy and line edge defects on the aluminum sidewalls.~ Superconducting quarter-wave resonators exhibit both saturable power dependence akin to conventional two-level-systems, and power independent loss that strongly impacts yield and is fabrication process dependent.~ Correlations between detailed electron microscopy, and resonator quality factor measurements with values above and below 10\textasciicircum 6 will be discussed. [Preview Abstract] |
Thursday, March 5, 2015 10:00AM - 10:12AM |
S39.00009: Characterization of Fabrication Defects in Superconducting Epitaxial Aluminum Resonators Nathan Siwak, Lei He, Justin Hackley, Christopher Richardson A continuing challenge in superconducting quantum computing is the creation of low-loss superconducting aluminum resonators. Significant processing difficulties lie in the removal of residues resulting from conventional Cl-based plasma etching without damaging the aluminum patterns. Correlations of resist residues and corrosion pit defect densities with cleaning process variations are completed using charge contrast-enhanced imaging in a scanning electron microscope. These quantified defects provide insight into the effectiveness of specific device processing steps in reducing these artifacts which can introduce additional loss mechanisms and limit potentially high performance devices. [Preview Abstract] |
Thursday, March 5, 2015 10:12AM - 10:24AM |
S39.00010: Effects of 780 nm Optical Illumination on Loss in Superconducting Microwave Resonator R.P. Budoyo, J.B. Hertzberg, C.J. Ballard, K.D. Voigt, J.E. Hoffman, J.A. Grover, P. Solano, J. Lee, S.L. Rolston, L.A. Orozco, J.R. Anderson, C.J. Lobb, F.C. Wellstood Understanding the effects of light incident on a superconducting circuit is an important step toward building a hybrid quantum system where a superconducting qubit or resonator is coupled to atoms trapped on a tapered optical fiber. We fabricated a microscale thin-film Al superconducting LC resonator (frequency 6.72 GHz) on sapphire substrate and mounted it inside an Al 3d cavity (TE101 mode frequency 7.50 GHz). Using an optical fiber, we illuminated the resonator with 780 nm light, and measured the change in internal quality factor and resonant frequency of the resonator as a function of applied optical power. The results suggest that the illumination causes an increase in rf drive-dependent dissipation. While optical illumination is expected to enhance dissipation due to quasiparticles, rf drive dependence is more typically seen in two-level-system dissipation. We compare the results with the change in loss from increased resonator temperature, and discuss various mechanisms of loss from optical illumination. [Preview Abstract] |
Thursday, March 5, 2015 10:24AM - 10:36AM |
S39.00011: Position-Dependent Optical Response of a Superconducting Resonator at 15 mK K. D. Voigt, J. B. Hertzberg, J. E. Hoffman, J. A. Grover, J. Lee, P. Solano, R. P. Budoyo, C. Ballard, J. R. Anderson, C. J. Lobb, L. A. Orozco, S. L. Rolston, F. C. Wellstood We have studied the optical and dielectric response of a translatable thin-film lumped-element superconducting Al microwave resonator cooled to 15 mK. The resonator has a resonance frequency of 6.14 GHz, a quality factor Q of 2.59 x 10$^{5\, }$and is mounted inside a superconducting aluminum 3D cavity. A tapered optical fiber enters and exits the 3D cavity through two small holes in opposite sides of the cavity, placed so that the fiber can pass close to the resonator. The 3D cavity is mounted on an x-z piezo-translation stage that allows us to change the relative position of the lumped-element resonator and fiber. When the resonator is brought near to the fiber, we observe a shift in resonance frequency due to the presence of the fiber dielectric. When light is sent through the fiber, Rayleigh scattering causes a position-dependent illumination of the resonator, generating quasiparticles and thereby affecting its resonance frequency and Q. Our model of the resonator response includes the generation, diffusion, and recombination of quasiparticles in the resonator and shows that the frequency response allows us to track the position of the fiber in situ. [Preview Abstract] |
Thursday, March 5, 2015 10:36AM - 10:48AM |
S39.00012: Robustness of superconducting high-Q resonators against direct quasiparticle injection U. Patel, I. Nsanzineza, B. L. T. Plourde, R. McDermott A longstanding goal of the superconducting qubit community is to integrate a superconducting quantum circuit with classical cryogenic digital logic based on the Single Flux Quantum (SFQ) logic family. Since the SFQ circuit transitions to the finite voltage state, care must be taken to protect the quantum circuit against quasiparticle-induced decoherence. Here we describe experiments to characterize the robustness of high-Q superconducting linear resonators against direct quasiparticle injection. We use NIS junctions to controllably inject quasiparticles into the groundplane of a superconducting resonator chip. We monitor resonator Q and frequency shift versus injection current for different device geometries. Finally, we discuss strategies to protect the resonator circuit from quasiparticle poisoning. [Preview Abstract] |
Thursday, March 5, 2015 10:48AM - 11:00AM |
S39.00013: Energy relaxation in transmons coupled to superconducting lumped-element resonators B. Suri, S. Novikov, F.C. Wellstood, B.S. Palmer We report on the energy relaxation of a series of Al/AlO$_{\mathrm{x}}$/Al transmon qubits coupled to superconducting Al lumped-element resonators on a sapphire substrate measured at 20 mK. For some of our transmon devices, which have transition frequencies between 4 and 8 GHz, we find that the coupling of the transmon to the 50 $\Omega$ transmission line through the lumped-element resonator is the dominant mechanism of relaxation limiting the lifetimes to 1 $\mu$s or smaller. By increasing the resonator's resonant frequency from 5.4 to 7.2 GHz, increasing the loaded quality factor of the resonator, and lowering the transmon-resonator coupling, we were able to decouple the transmon from the dissipative environment by an order of magnitude. We observe an improvement in the lifetimes of the transmon, with new limits possibly set by material losses. Microwave simulations, analytical results and experimental measurements on multiple devices will be presented. [Preview Abstract] |
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