Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session P26: Superconducting Qubits: Materials / Nanomechanical Resonators |
Hide Abstracts |
Sponsoring Units: GQI Chair: David Schuster, Yale University Room: D136 |
Wednesday, March 17, 2010 8:00AM - 8:12AM |
P26.00001: Superconducting microwave resonators - low loss, tunability, and coupling Haohua Wang, Radoslaw C. Bialczak, Mike Lenander, Erik Lucero, Matteo Mariantoni, Matthew Neeley, Aaron O'Connell, Daniel Sank, Martin Weides, James Wenner, Tsuyoshi Yamamoto, Yi Yin, Andrew Cleland, John Martinis The superconducting microwave resonator is an important device for applications such as quantum computation and photon detection. A key parameter characterizing its performance is the energy decay time. We have optimized our superconducting coplanar resonators to achieve an energy decay time around 10 $\mu$s. By fabricating devices with different metals and measuring their quality factors as a function of temperature, power, and cooling field, we have identified an important dissipation mechanism: loss from two-level states at metal-oxide surfaces. We also find that the (classical) measurement of the quality factor at low power is consistent with the energy decay time measured in a (quantum) qubit-resonator swap experiment. Further experiments on tuning the resonator frequency while minimizing dissipation, as well as coupling two resonators, will also be discussed. [Preview Abstract] |
Wednesday, March 17, 2010 8:12AM - 8:24AM |
P26.00002: Improved Josephson Qubits incorporating Crystalline Silicon Dielectrics Yuanfeng Gao, Leon Maurer, David Hover, Umeshkumar Patel, Robert McDermott Josephson junction phase quibts are a leading candidate for scalable quantum computing in the solid state. Their energy relaxation times are currently limited by microwave loss induced by a high density of two-level state (TLS) defects in the amorphous dielectric films of the circuit. It is expected that the integration of crystalline, defect-free dielectrics into the circuits will yield substantial improvements in qubit energy relaxation times. However, the epitaxial growth of a crystalline dielectric on a metal underlayer is a daunting challenge. Here we describe a novel approach in which the crystalline silicon nanomembrane of a Silicon-on-Insulator (SOI) wafer is used to form the junction shunt capacitor. The SOI wafer is thermocompression bonded to the device wafer. The handle and buried oxide layers of the SOI are then etched away, leaving the crystalline silicon layer for subsequent processing. We discuss device fabrication issues and present microwave transport data on lumped-element superconducting resonators incorporating the crystalline silicon. [Preview Abstract] |
Wednesday, March 17, 2010 8:24AM - 8:36AM |
P26.00003: Transport Characteristics of co-Deposited Alumina Barriers in Nb-AlOx-Nb Josephson Junctions Allison F. Dove, Gustaf A. Olson, Brian Enders, Chris D. Nugroho, Vladimir Orlyanchik, Dale J. Van Harlingen, James N. Eckstein A major contributor to dephasing in superconducting qubits are dynamical charge defects. A likely source of charge defects in these qubits are oxygen deficiencies in the insulating barrier of the Josephson junctions that modulate their critical current. When such barriers are grown by diffusion of oxygen, it is thought that there are more oxygen deficiencies than when the barriers are grown by co-deposition of metal and oxygen. We use molecular beam epitaxy and an oxygen source to grow alumina barriers in niobium-alumina-niobium sandwich-style Josephson junctions. Because transport characteristics serve as a good initial measure of the insulating barrier quality, we report transport characteristics of devices with various barrier properties. The low-frequency noise properties of these junctions will also be measured and correlated with junction parameters. [Preview Abstract] |
Wednesday, March 17, 2010 8:36AM - 8:48AM |
P26.00004: Thin film processing of Re/Al$_{2}$O$_{3}$/Re/Ru epitaxial trilayers into superconducting qubits Jeffrey S. Kline, Fabio da Silva, David S. Wisbey, Michael R. Vissers, David P. Pappas We present a new recipe for processing thin film Re/Al$_{2}$O$_{3}$/Re/Ru epitaxial trilayers into superconducting qubits. To maintain compatibility with current in-plane tunneling (CIPT) measurements, we use a thin top electrode consisting of 30 nm Re and 5 nm Ru. The Ru cap protects the Re film underneath from tarnishing when exposed to atmosphere and has an electrically conductive native oxide. The Ru cap also protects the mesa from unwanted etching during the overetch portion of the CHF$_{3}$+O$_{2}$ reactive ion etch (RIE) used for the via etch of the SiO$_{2}$ insulator layer. Unintentional sidewall redeposition of base and top electrode material during the mesa etch is avoided through the use of a two step process. First the Ru cap is argon ion milled, but the tunnel barrier is not breached. Next, the Re top electrode and Al$_{2}$O$_{3}$ tunnel barrier are etched by an SF$_{6}$ RIE. We compare RA-products measured by CIPT (trilayer unprocessed) to RA-products obtained from tunnel junctions processed using our new recipe. [Preview Abstract] |
Wednesday, March 17, 2010 8:48AM - 9:00AM |
P26.00005: Thin film growth of epitaxial Re/Al$_{2}$O$_{3}$/Re/Ru trilayers for fabrication into Josephson junction based phase qubits Michael R. Vissers, Jeffrey S. Kline, Fabio da Silva, David S. Wisbey, William F. Egelhoff, David Pappas We present a new growth recipe for creating single crystal thin film Re/Al$_{2}$O$_{3}$/Re/Ru epitaxial trilayers for fabrication into Josephson junctions, a critical component of the phase qubit circuit.~ The crystalline aluminum oxide barrier is sputter deposited at high temperature, and pinholes in the barrier can be reduced by tuning the oxygen concentration present during the sputtering process.~ The thickness of the Al$_{2}$O$_{3}$ barrier is monitored \textit{in situ} using multi-wavelength ellipsometry.~ To maintain compatibility with current in-plane tunneling (CIPT) measurements, the thin top electrode is designed to consist of 30 nm Re and 5 nm Ru. The passivating Ru cap protects the underlying Re film from tarnishing when exposed to atmosphere, and also forms a conductive native oxide.~ CIPT measurements permit the study of the barrier tunneling characteristics prior to the wafer being processed into junctions.~ We utilize the RA products obtained from both the CIPT measurements and the fabricated tunnel junctions to optimize the trilayer growth architecture and procedure. This work was funded by the U.S. government and IARPA. [Preview Abstract] |
Wednesday, March 17, 2010 9:00AM - 9:12AM |
P26.00006: Dielectric Loss Studies of New Materials for Quantum Information Circuits David Wisbey, Fabio da Silva, Jeffery S. Kline, Michael Vissers, Sudarshan Karki, Anthony Caruso, Jiansong Gao, David P. Pappas Boron carbide was deposited on a niobium thin film multiplexed coplanar waveguide resonators and the unsaturated internal quality factor was measured. At high power the internal quality factor was 120,000 but at low power, in the single photon regime (unsaturated), it dropped to below 10,000 indicating the presence of two level systems in the boron carbide. Also the internal quality factor of crystalline rhenium multiplexed coplanar waveguides, with a 2 nm crystalline aluminum oxide capping layer, was measured and had an unsaturated internal quality factor of 85,000. The best overall resonator, considering internal unsaturated quality factor and ease of processing, was found to be a high quality niobium thin film grown on a highly ordered sapphire substrate with the highest unsaturated quality factor of 160,000. [Preview Abstract] |
Wednesday, March 17, 2010 9:12AM - 9:24AM |
P26.00007: Microbridge junctions for superconducting phase qubits Martin Weides, R. C. Bialczak, M. Lenander, E. Lucero, M. Mariantoni, M. Neeley, A. O'Connell, D. Sank, H. Wang, J. Wenner, T. Yamamoto, Y. Yin, A. Cleland, J. Martinis Josephson junctions for superconducting circuits such as SQUIDs and qubits are conventionally based on Al-AlO$_x$-Al multilayer technology, which has two-level-fluctuators in the dielectric AlO$_x$ as a limiting decoherence source. Replacing the tunnel junction with a nano-structured microbridge junction based on a hardly oxidizable metal, e.g. rhenium, is a potential solution to reduce the intrinsic noise level. Being capacitively shunted, the microbridge junctions cubic potential allows for the operation as a phase qubit and to use its quantum limited energy resolution as a sensor for residual electronic fluctuations. In this talk, transport measurements on microbridge junctions, structured with Focus Ion Beam and Electron Beam Lithography, their potential as active elements in superconducting circuits, as well as preliminary data for microbridge phase qubits will be presented. [Preview Abstract] |
Wednesday, March 17, 2010 9:24AM - 9:36AM |
P26.00008: Novel qubit test platform Fabio da Silva, Dale Li, Danielle Braje, Raymond Simmonds, Thomas Ohki, David Pappas Current research linking superconducting qubit coherence to materials composition motivates the exploration of novel media for qubit circuit fabrication. However, in an integrated measurement structure, any changes in the qubit materials invariably affect the design, processing, operation, and yield of the supporting measurement circuitry. We address this problem by splitting the qubit circuit, namely, the qubit loop and the excitation/ measurement circuitry. We achieve this by fabricating the qubit on a separate chip, flipping it over, and precision aligning it to the measurement circuitry chip. This allows us to use any material and processing for the qubit. We show that the excitation/measurement chip works robustly (it can be used multiple times with different qubit chips), is reliable (typical qubit measurements were successfully performed), and flexible (allows for the control of different coupling strengths to the qubit). [This work was supported by IARPA and other grants by the U.S. Government.] [Preview Abstract] |
Wednesday, March 17, 2010 9:36AM - 9:48AM |
P26.00009: Preparation and Detection of an r.f. Mechanical Resonator Near the Motional Ground State Tristan Rocheleau, Tchefor Ndukum, Keith Schwab We have cooled the motion of a 6.2 MHz nanomechanical resonator by parametrically coupling it to a 7.5 GHz superconducting resonator. Starting from a thermal occupation of ~500 quanta, we have observed occupation factors as low as 3.8 +/- 1.2 and expect the mechanical motion to be found with probability 0.21 in the quantum ground state of motion. We will describe the factors which are limiting further cooling and progress towards colder states of motion. By measuring differences in up and down-conversion of microwave photons in a process analogous to Raman scattering, we expect to observe fundamental quantum behavior of the nanomechanics. [Preview Abstract] |
Wednesday, March 17, 2010 9:48AM - 10:00AM |
P26.00010: Nanomechanical motion measured with an imprecision below the standard quantum limit using a nearly shot-noise limited microwave interferometer Jennifer Harlow, John Teufel, Tobias Donner, Manuel Castellanos-Beltran, Konrad Lehnert Observing quantum behavior of mechanical motion is challenging because it is difficult both to prepare pure quantum states of motion and to detect those states with sufficient precision. We present displacement measurements of a nanomechanical oscillator with an imprecision below that at the standard quantum limit [1]. We infer the motion from the phase modulation imprinted on a microwave signal by that motion. The modulation is enhanced by embedding the oscillator in a high-Q microwave cavity. We achieve the low imprecision by reading out the modulation with a Josephson Parametric Amplifier, realizing a microwave interferometer that operates near the shot-noise limit. The apparent motion of the mechanical oscillator due the interferometer's noise is now substantially less than its zero-point motion, making future detection of quantum states feasible. In addition, the phase sensitivity of the demonstrated interferometer is 30 times higher than previous microwave interferometers, providing a critical piece of technology for many experiments investigating quantum information encoded in microwave fields. [1] J. D. Teufel, T. Donner, M. A. Castellanos-Beltran, J. W. Harlow, K. W. Lehnert, Nature Nanotechnology, doi:10.1038/nnano.2009.343, (2009). [Preview Abstract] |
Wednesday, March 17, 2010 10:00AM - 10:12AM |
P26.00011: Back-action Evading Measurements of a Nanomechanical Resonator Tchefor Ndukum, Tristan Rocheleau, Keith Schwab By driving a 5GHz superconducting, co-planar waveguide (CPW) resonator coupled to a radio-frequency nanomechanical resonator with both red and blue-detuned, phase coherent microwave signals, we have demonstrated amplifier noise back-action evading (BAE) detection of one quadrature of nanomechanical motion. With this quantum non-demolition (QND) scheme we have shown precise measurements of a single motional quadrature with additive measurement noise of 4 times the zero point amplitude, and a reduction in sensitivity to injected measurement noise of a factor of 43 in comparison to a single tone, non-BAE measurement. By increasing the CPW frequency to 7.5GHz, quadrupling the coupling strength and improving the (internal) quality factor of the CPW, we expect to be able to demonstrate sensitivity to one quadrature with additive measurement noise below the zero-point level, a necessary ingredient to produce and measure squeezed states of motion. [Preview Abstract] |
Wednesday, March 17, 2010 10:12AM - 10:24AM |
P26.00012: Micromechanical Membranes Coupled to Superconducting Microwave Resonators John Teufel, Dale Li, Katarina Cicak, Shane Allman, Fabio Altomare, Jed Whittaker, Adam Sirois, Raymond Simmonds We will present preliminary results on fabrication and characterization of the mechanical properties freely suspended aluminum membranes at ultralow temperatures. The radio-frequency vibrational modes are detected by dispersively coupling membranes to superconducting microwave circuits. The resulting microwave optomechanical system provides excellent displacement and force sensitivity, as well as the ability to use resolved sideband cooling to prepare the mechanical degree of freedom near its quantum ground state. We will discuss initial results and future experiments which will couple these mechanical oscillators to superconducting qubits. [Preview Abstract] |
Wednesday, March 17, 2010 10:24AM - 10:36AM |
P26.00013: Introduction of a DC Bias into a High-Q Microwave Cavity Weiwei Xue, Fei Chen, Ian Hayes, M.P. Blencowe, A.J. Rimberg The circuit quantum electrodynamics (QED) architecture has been demonstrated to allow study cavity QED physics in a high-Q on- chip microwave cavity[1]. Here we develop a technique to apply a DC current or voltage bias to nanostructures embedded in the microwave cavity without significantly disturbing the cavity modes or degrading the Q at high frequencies. The DC biasing scheme will be discussed. Experimental results show good agreement with theoretical predictions. New highly non- linear fully quantum mechanical devices can be developed by embedding Josephson junction devices such as Superconducting Quantum Interference Devices (SQUIDs) or single electron transistors (SETs) in the high-Q microwave cavity. Furthermore, by integrating a nanomechanical resonator, such cavities may also be used to investigate the quantum to classical transition. [1] A. Wallraff et al, Nature, 431, 162 (2004). [Preview Abstract] |
Wednesday, March 17, 2010 10:36AM - 10:48AM |
P26.00014: Superconducting Single Electron Transistor Coupled to a DC-Biased High-Q Microwave Cavity Fei Chen, Weiwei Xue, Ian Hayes, M.P. Blencowe, A.J. Rimberg DC biased high-Q microwave cavities based on the circuit quantum electrodynamics (QED) architecture [1] have been developed, allowing simultaneous particle and photon exchange with nanostructures placed in a 1-D transmission line resonator. Here we embed superconducting single electron transistors (S-SETs) in such a cavity. The interplay between the S-SET and the microwave cavity offers an interesting system for studying nonlinear quantum dynamics and the quantum-to-classical transition. We fabricate the S-SET using cryogenic ultra-thin film evaporation techniques. The S-SET is directly coupled to the center conductor of the transmission line resonator, allowing application of a DC bias across the S-SET. The highly tunable nonlinearity can be accessed by using a small DC bias such that the S-SET remains in the supercurrent regime. Recent experimental results will be discussed. [1] A. Wallraff et al, Nature, 431, 162 (2004). [Preview Abstract] |
Wednesday, March 17, 2010 10:48AM - 11:00AM |
P26.00015: A macroscopic mechanical resonator operated in the quantum limit Aaron O'Connell, Radoslaw Bialczak, Michael Lenander, Erik Lucero, Matteo Mariantoni, Matthew Neeley, Daniel Sank, Haohua Wang, Martin Weides, James Wenner, Tsuyoshi Yamamoto, Yi Yin, John Martinis, Andrew Cleland The observation of quantum effects in a macroscopic mechanical resonator is hindered by the difficulty in cooling to the quantum ground state, and in making a system that displays adequate coherence times. We are able to meet these challenges in a novel system comprising a superconducting phase qubit coupled to a high frequency (6 GHz) micromechanical dilatational resonator. Using this coupled system, we place an upper bound on the minimum average phonon occupation number of the mechanical resonator $\langle n \rangle < 0.07$, showing that the resonator is in its quantum ground state. Furthermore, we use the qubit to both create and measure a single phonon state in the resonator. Using this ability, the energy decay and phase coherence times of the resonator are extracted. Additionally, we excite the resonator directly with a classical microwave source, demonstrably creating a coherent state in the mechanical resonator. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700