Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Z29: Focus Session: Superconducting Qubits - Coherence and Materials III |
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Sponsoring Units: GQI Chair: John Teufel, National Institute of Standards and Technology Room: C148 |
Friday, March 25, 2011 11:15AM - 11:27AM |
Z29.00001: Improving the Quality Factor of Microwave Compact Resonators K. Geerlings, S. Shankar, E. Edwards, L. Frunzio, R.J. Schoelkopf, M.H. Devoret Superconducting microwave resonators are now widely used for coupling to superconducting qubit systems. Compact resonators [1] consisting of an interdigitated capacitance and a meander inductance take up much less space than a typical coplanar waveguide resonator. Since the design of compact resonators and qubits share common features, qubit decoherence mechanisms can be studied through the measurement of resonator loss. We measured of order 100 resonators and have achieved internal quality factors in excess of 300,000. Results indicate loss appears to be due to spurious two level systems. Loss increases when the participation of surfaces in the energy density is increased. Thus a large separation of electrodes is preferred, in agreement with the findings of other groups. Work in progress involves the combination of these resonators with transmon qubits. Work supported by IARPA, ARO and the NSF. \\[4pt] [1] M.S. Khalil, F.C. Wellstood, and K.D. Osborn, arXiv:1008.2929 [Preview Abstract] |
Friday, March 25, 2011 11:27AM - 11:39AM |
Z29.00002: Radiative Losses in Superconducting Coplanar Resonators James Wenner, R. Barends, R.C. Bialczak, Y. Chen, J. Kelly, M. Lenander, E. Lucero, M. Mariantoni, M. Neeley, A.D. O'Connell, P. O'Malley, D. Sank, A. Vainsencher, H. Wang, M. Weides, T. White, Y. Yin, J. Zhao, A.N. Cleland, John M. Martinis Radiation is a potential loss mechanism in superconducting qubits. Radiation loss was studied in superconducting coplanar resonators, which are important both in coupling superconducting qubits and because they provide a simple system to quantitatively measure the resulting effects. We fabricated 8 GHz resonators and measured the resulting reduction of the high-power Q. We found it was necessary to design the resonators carefully to reduce stray coupling between the resonators so that losses would be dominated by radiation. The radiation loss is measured to be 30 times greater than predicted by a simple theoretical model, but was predicted accurately by simulation data. We attribute this to the effects of the device mount and the finite substrate height on the radiation pattern. We conclude that radiation is an unlikely decoherence mechanism for the present generation of qubits and resonators. [Preview Abstract] |
Friday, March 25, 2011 11:39AM - 11:51AM |
Z29.00003: Minimal resonator loss for circuit quantum electrodynamics Rami Barends, N. Vercruyssen, A. Endo, P.J. de Visser, T. Zijlstra, T.M. Klapwijk, P. Diener, S.J.C. Yates, J.J.A. Baselmans, H. Wang, M. Hofheinz, J. Wenner, M. Ansmann, R.C. Bialczak, M. Lenander, E. Lucero, M. Neeley, A.D. O'Connell, D. Sank, M. Weides, A.N. Cleland, J.M. Martinis In Josephson quantum information processing superconducting coplanar waveguides are used as memory elements and coupling buses. Quality factors of these resonators reach up to a million at high excitation powers, but decrease down to below 100x10$^3$ at the single photon level in the presently used materials, such as Al and Nb. We report quality factors of up to 500x10$^3$ by using NbTiN or Re and removing the dielectric from regions with high electric fields. Using a model-analysis and by a comparison with Ta, the crucial sources of intensity-dependent loss are dielectrics on the surface of the metal and substrate. Our approach shows that using non-oxidizing superconductors such as Re and NbTiN and removing dielectrics is a straightforward route to high quality factors in the single photon regime. [Preview Abstract] |
Friday, March 25, 2011 11:51AM - 12:03PM |
Z29.00004: Low-loss superconducting microwave resonators with NbN films C. Song, B. Xiao, M. Ware, B.L.T. Plourde The native oxide that forms on the surface of most superconducting thin films contains a distribution of two-level system (TLS) defects that results in a significant microwave loss channel at low temperatures and powers. One of the key limitations in the quality factor of microwave devices in this regime for superconducting quantum information processing schemes is due to this surface loss mechanism. Thus, nitride superconducting materials are promising candidates due to their lack of a significant surface oxide. We have fabricated coplanar waveguide microwave resonators from reactively sputtered NbN films on sapphire and Si substrates. We characterize the resonators with measurements of the center frequency and quality factor as a function of temperature and power. In the low-temperature and low-power limit, we have observed quality factors for NbN resonators in excess of 200,000. [Preview Abstract] |
Friday, March 25, 2011 12:03PM - 12:15PM |
Z29.00005: Low Loss Superconducting Titanium Nitride Coplanar Waveguide Resonators Michael Vissers, David Wisbey, Jiansong Gao, Jeffrey Kline, Martin Weides, David Pappas The introduction of new, low loss superconducting materials will be necessary for the improvement of superconducting qubits. To fulfill this aim, thin films of titanium nitride (TiN) were sputter-deposited onto intrinsic Si and c-plane sapphire wafers with and without SiN buffer layers. The films were then fabricated into RF coplanar waveguide resonators, and internal quality factor measurements were taken at millikelvin temperatures in both the high and low power limits, i.e. many and single photon regimes, respectively. At high power, internal quality factors (Qi's) higher than 10$^7$ were measured for multiple TiN films with a predominantly (200) orientation. Films that showed significant (111) texture invariably had much lower Qi's in this regime, on the order of 10$^5$. Our studies show that the (200) TiN is favored for growth at high temperature on either bare Si or substrates with SiN buffer layers. However, growth on bare sapphire or Si (100) at low temperature resulted in primarily a (111) orientation. Ellipsometry and Auger measurements indicate that the (200) TiN growth on the bare Si substrates is correlated with the formation of a thin, $\sim $2nm, layer of SiN during the pre-deposition procedure. We found that TiN grown on these surfaces also showed significant increases of Qi in the low power limit, while thicker SiN buffer layers resulted in reduced Qi's. [Preview Abstract] |
Friday, March 25, 2011 12:15PM - 12:27PM |
Z29.00006: Dielectric loss measurements using an embedded transmission line resonator Bahman Sarabi, M.J.A. Stoutimore, Moe Khalil, Sergiy Gladchenko, Alexander Kozen, Gary Rubloff, F.C. Wellstood, J.C. Lobb, K.D. Osborn Lossy dielectrics are a major source of decoherence in superconducting qubits. Superconducting linear resonators have proven to be ideally suited for measuring loss in different dielectrics due to their versatility and relative simplicity in design, fabrication, and measurement. We will present data from samples where the low-loss coplanar resonators are fabricated on top of AlOx dielectric films grown using atomic layer deposition (ALD). Although the low-power loss can be extracted from this geometry, embedding the dielectric under study between metal films has advantages that we will discuss. In addition, ALD films can be grown conformally and without pinholes to small thicknesses in comparison to conventional PECVD films. This allows us to make lumped-element resonators with a relatively small footprint, which can easily be embedded within the transmission line. [Preview Abstract] |
Friday, March 25, 2011 12:27PM - 12:39PM |
Z29.00007: Design and Fabrication of High Q Titanium Nitride Resonators David Wisbey, Jiansong Gao, Michael Vissers, Jeffrey Kline, Martin Weides, David Pappas Titanium nitride (TiN) is a new material that shows promise in quantum information circuits as a low loss material for resonators, and as a multiplexed kinetic inductance photon detector. We have measured lumped element LC resonators and coplanar waveguides resonators. For the lumped element resonator we report internal quality factor (Qi) of over 300,000 at low power, in the single photon regime, and 4 million at high power, and for a half wave coplanar waveguide we report low power Qi of 800,000 and high power Qi of 5 million. We found that overetch in single layer devices can shift the resonance frequency and affect the internal quality factor Qi, and that as the trench depth grew, both the resonance frequency and internal quality factor increased. When designing resonators it is important to know quantities such as the kinetic inductance, superconducting transition temperature (Tc), penetration depth, and amount of overetch so the resonator can be accurately simulated. [Preview Abstract] |
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