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Displaying 51 - 75 of 104

Effect of metal/substrate interfaces on radio-frequency loss in superconducting coplanar waveguides

November 8, 2010
Author(s)
David S. Wisbey, Jiansong Gao, Fabio C. da Silva, Jeffrey S. Kline, Michael Vissers, David P. Pappas, Leila R. Vale
Microscopic two-level systems (TLSs) are known to contribute to loss in resonant superconducting microwave circuits. This loss increases at low power and temperatures as the TLSs become unsaturated. We find that the loss is dependent on both the substrate

Remote sensing and control of phase qubits

September 10, 2010
Author(s)
Dale Li, Fabio C. Da Silva, Danielle Braje, Raymond W. Simmonds, David P. Pappas
We demonstrate a remote sensing design of phase qubits by separating the control and readout circuits from the qubit loop. This design improves measurement reliability because the control readout chip can be fabricated using more robust materials and can

Direct Observation of Coherent Population Trapping in a Superconducting Artificial Atom

April 20, 2010
Author(s)
David P. Pappas, Jeffrey S. Kline, Willim R. Kelley, Zachary Dutton, Thomas A. Ohki, john Schlafer, Bashkar Mookerji
The phenomenon of coherent population trapping (CPT) of an atom (or solid state artificial atom ), and the associated effect of electromagnetically induced transparency (EIT), are clear demonstrations of quantum interference due to coherence in multilevel

Thin lm dielectric microstrip kinetic inductance detectors

March 8, 2010
Author(s)
David P. Pappas, Jiansong Gao, Benjamin Mazin, Daniel Sank, Erik Lucero, John M. Martinis, Andrew Merrill, Sunil Golwala, David Moore, Jonas Zmuidzinas
Microwave Kinetic Inductance Detectors, or MKIDs, are a type of low temperature detector that exhibit intrinsic frequency domain multiplexing at microwave frequencies. We present theory and measurements on a new type of MKID based on a microstrip

Normal-state conductance used to probe superconducting tunnel junctions for quantum computing

March 3, 2010
Author(s)
David P. Pappas, Jeffrey S. Kline, Seongshik Ohy, Carlos Chapraro, Richard Bavier, Yong Kim, Eunyoung Kim
Here we report normal-state conductance measurements of three different types of superconducting tunnel junctions that are being used or proposed for quantum computing applications: p-Al/a-AlO/p-Al, e-Re/e-AlO/p-Al, and e-V/e-MgO/p-V, where p stands for

Model of magnetic impurities within the Josephson junction of a phase qubita

December 23, 2009
Author(s)
David P. Pappas, R. P. Erickson
We consider a superconducting phase qubit consisting of a monocrystalline sapphire Josephson junction with symmetry axis perpendicular to the junction interfaces. Via the London gauge we present a theoretical model of Fe3+ magnetic impurities within the

Oersted Field Induced Magnetization Scissoring In Permalloy Bars

December 10, 2009
Author(s)
Lu Yuan, Fabio C. da Silva, Sean Halloran, Hamid Z. Fardi, David P. Pappas
We have systematically studied the magnetization behavior induced by the applied current in the permalloy (Ni81Fe19) bars using second and third harmonic analysis. Three types of sample were studied with layer structures of Al30/NiFe10, NiFe5/Al30/NiFe5

Magnetic Noise in a Low-Power Picotesla Magnetoresistive Sensor

October 25, 2009
Author(s)
Stephen E. Russek, Lu Yuan, Sean Halloran, Fabio C. da Silva, David P. Pappas, John M. Moreland, Sy-hwang Liou, Rui Zhang
We present a design of a low power, compact, magnetoresistive sensor. The key features of the design are(1) decreasing the noise by the use of a 64 element magnetic tunnel junction (MTJ) bridge,(2) reducing the magnetic noise by annealing the MTJ sensors

Modification of magnetotransport properties across patterned GaMnAs nanoconstrictions by application of high current densities

July 17, 2009
Author(s)
David P. Pappas, Fabio Cesar Da Silva, Teresa Osminer, Sung Un Cho, Hyung Choi, Chan Yang, Yun Park
We report on the modification of magnetotransport properties across patterned GaMnAs nanoconstrictions by the application of high current densities (< 107 A/cm2). We observe controllable changes in the electrical resistance with the direction of the bias

Josephson phase qubit circuit for the evaluation of advanced tunnel barrier materials

November 21, 2008
Author(s)
Jeffrey S. Kline, Haohua Wang, Seongshik Oh, John M. Martinis, David P. Pappas
We have found that crystalline Josephson junctions have critical current density control problems which decrease circuit yield. We present a qubit circuit designed to accommodate a factor-of-five variation in critical current density for the evaluation of

A z-component magneto-resistive sensor

April 8, 2008
Author(s)
Fabio C. da Silva, Sean Halloran, Lu Yuan, David P. Pappas
A thin-film sensor is described that measures the component of the magnetic field perpendicular to the plane of the substrate (also called the z-component field.) The sensors are fabricated on anisotropically etched, V-shaped groves on Si(100) substrates

Dependence of noise in magnetic tunnel junction sensors on annealing field and temperature

March 7, 2008
Author(s)
Stephen E. Russek, David P. Pappas, Sean Halloran, Lu Yuan, Sy-Hwang Liou, Rui Zhang
The minimum detectable field of magnetoresistive sensors is limited by their intrinsic noise. Magnetization fluctuations are one of the crucial noise sources and are related to the magnetization alignment at the antiferromagnetic – ferromagnetic interface

256-Channel Magnetic Imaging System

January 18, 2008
Author(s)
Fabio C. da Silva, Sean Halloran, Anthony B. Kos, David P. Pappas
We present the design and fabrication of a magentoresistive imaging system capable of measuring 256 channels simultaneously along linear ranges of 4 mm and 13 mm. The channels are interfaced by custom electronics and the images are displayed in real time

256-channel magnetic imaging system

January 15, 2008
Author(s)
Fabio C. Da Silva, Sean Halloran, Anthony B. Kos, David P. Pappas
We present the design and fabrication of a magnetoresistive imaging system capable of scanning 256 channels simultaneously along linear ranges of either 4 or 13 mm. High speed electronics read the channels and transfer the data to a computer that builds

Development of a thin film magnetic moment reference material

January 1, 2008
Author(s)
Robert R. Owings, Fabio C. Da Silva, David P. Pappas
This paper presents the results of an interlaboratory comparison and development of a magnetic moment reference material. The comparison was between the National Institute of Standards and Technology, magnetometer manufacturers, industrial, academic, and

Elimination of two level fluctuators in superconducting quantum bits by an epitaxial tunnel barrier

September 7, 2006
Author(s)
Seongshik Oh, Katarina Cicak, Jeffrey S. Kline, Mika Sillanpaa, Jed D. Whittaker, Raymond W. Simmonds, David P. Pappas, Kevin Osborn
Quantum computing based on Josephson junction technology is considered promising due to its scalable architecture. However, decoherence is a major obstacle. Here, we report evidence for improved Josephson quantum bits qubits using a single-crystal Al2O3

Josephson Junction Materials Research Using Phase Qubits

May 30, 2006
Author(s)
Raymond Simmonds, Dustin P. Hite, Robert McDermott, Matthias Steffen, Ken B. Cooper, Kristine Lang, John M. Martinis, David P. Pappas
At present, the performance of superconducting qubits is limited by decoherence. Strong decoherence of phase qubits is associated with spurious microwave resonators residing within the Josephson junction tunnel barrier [1]. In this work, we investigate

Erbium-doped Gold Sensor Films for Magnetic Microcalorimeter X-ray Detectors*

April 17, 2006
Author(s)
Barry L. Zink, Kent D. Irwin, Gene C. Hilton, Joel Ullom, David P. Pappas
We briefly review the principles of a magnetic microcalorimeter x-ray detector and the requirements for fabricating an array of these sensors, which include a paramagnetic sensor fabricated with thin-film techniques. We discuss two methods for depositing

Decoherence in Josephson Qubits from Dielectric Loss

November 16, 2005
Author(s)
John M. Martinis, Ken B. Cooper, Robert Mcdermott, Matthias Steffen, Markus Ansmann, Kevin Osborn, Katarina Cicak, Seongshik Oh, David P. Pappas, Raymond Simmonds, Clare Yu
Dielectric loss from two-level states is shown to be a dominant decoherence source in superconducting quantum bits. Depending on the qubit design, dielectric loss from insulating materials or the tunnel junction can lead to short coherence times. We show

Epitaxial growth of rhenium with sputtering

October 6, 2005
Author(s)
Seongshik Oh, Dustin P. Hite, Katarina Cicak, Kevin Osborn, Raymond W. Simmonds, Robert Mcdermott, Ken B. Cooper, Matthias Steffen, John M. Martinis, David P. Pappas
We have grown epitaxial renium (0001) films on α-Al 2O 3(0001) substrates using sputter deposition in an ultra high vacuum system. We find that better epitaxy is achieved with DC rather than with RF sputtering. With DC sputtering, epitaxy is obtained with

Low-Leakage Superconducting Tunnel Junctions with a Single-Crystal Al2O3 Barrier

September 5, 2005
Author(s)
Seongshik Oh, Katarina Cicak, Kevin Osborn, Raymond Simmonds, David P. Pappas, Robert Mcdermott, Ken B. Cooper, Matthias Steffen, John M. Martinis
We have developed a two-step growth scheme for single-crystal Al2O3 tunnel barriers. The barriers are epitaxially grown on single-crystal rhenium (Re) base electrodes that are grown epitaxially on a sapphire substrate, while polycrystalline Al is used as

Low-frequency noise measurements on commercial magnetoresistive magnetic field sensors

May 17, 2005
Author(s)
Nathan Stutzke, Stephen E. Russek, David P. Pappas, Mark Tondra
Low frequency noise was measured in the frequency range from 0.1 Hz to 10 kHz on a variety of commercially available magnetic sensors. The types of sensors investigated include anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), and tunnel