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Search Publications by: Joe Aumentado (Fed)

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Displaying 26 - 46 of 46

The Cooper Pair Transistor

September 17, 2010
Author(s)
Jose A. Aumentado
The Cooper pair transistor (CPT) is a superconducting electrometer that has applications in quantum information as well as fundamental superconductivity studies. Since it operates in a near-dissipationless mode, it has potential as a minimally invasive

Energy Decay in Josephson Qubits from Non-equilibrium Quasiparticles

August 26, 2009
Author(s)
Jose A. Aumentado, John M. Martinis, M Ansmann
We calculate the energy decay rate of Josephson qubits and superconducting resonators from non-equilibrium quasiparticles. The decay rates from experiments are shown to be consistent with our predictions based on a prior measurement of the quasiparticle

Phase Locking Transition in a Chirped Superconducting Josephson Resonator

September 12, 2008
Author(s)
Jose A. Aumentado, Ofer Naaman, L Friedland, J.S. Wurtele, Irfan Siddiqi
We observe a sharp threshold for autoresonant phase locking in a transmission line resonator embedded with a Josephson tunnel junction and driven with a purely ac, chirped microwave signal. When the drive amplitude is below a critical value, the resonator

Narrow band microwave radiation from a biased single-Cooper-pair transistor

May 29, 2007
Author(s)
Ofer Naaman, Joe Aumentado
We show that a single-Cooper-pair transistor (SCPT) electrometer emits narrow-band microwave radiation when biased in its sub-gap region. Photo-activation of quasiparticle tunneling in a nearby SCPT is used to spectroscopically detect this radiation, in a

VARIABILITY OF CHARGE NOISE IN Al-BASED SET TRANSISTORS

July 14, 2006
Author(s)
Mark W. Keller, Blaise Jeanneret, Joe Aumentado
We measured the charge noise of four Al-based SET transistors on multiple cooldowns. We found a consistent 1/f component independent of thermal cycling and other treatments, but large variations in the total noise spectrum due to two-level fluctuators.

Poisson transition rates from time-domain measurements with finite bandwidth

March 17, 2006
Author(s)
Ofer Naaman, Joe Aumentado
We show that in realistic time-domain measurements of a Poisson two-level system, the observed transition rates are renormalized downwards due to the finite bandwidth of the experiment. This effect introduces systematic errors in estimating the system''s

Zigzag-shaped magnetic sensors

December 13, 2004
Author(s)
Fabio C. da Silva, Willard C. Uhlig, Anthony B. Kos, Susan A. Schima, Joe Aumentado, John Unguris, David P. Pappas
Magnetism in zigzag-shaped thin-film elements is investigated using scanning electron microscopy with polarization analysis, magnetotransport measurements, and micromagnetic simulations. We find that the angle of magnetization alternates along the length

Nonequilibrium Quasiparticles and Periodicity in Single-Cooper-Pair Transistors

February 13, 2004
Author(s)
Joe Aumentado, Mark W. Keller, John M. Martinis, Michel H. Devoret
We have made single-Cooper-pair transistors in which we control the spatial profile of the superconducting gap energy by oxygen doping. The profile dramatically affects the switching current vs. gate voltage curve of the transistor, changing its period

Zigzag Shaped Magnetic Sensors

January 1, 2004
Author(s)
S da, Willard C. Uhlig, A Kos, Joe Aumentado, Michael J. Donahue, John Unguris, David P. Pappas
Magnetism in zigzag shaped thin film elements is investigated using scanning electron microscopy with polarization analysis, magneto-transport measurements, and micromagnetic simulations. We find that the angle of magnetization alternates along the length

Banishing Quasiparticles From Josephson-Junction Qubits: Why and How To Do It

June 1, 2003
Author(s)
Kristine Lang, Sae Woo Nam, Joe Aumentado, John M. Martinis, C Urbina
Current-biased Josephson junctions are prime candidates for the implementation of quantum bits; however, a present limitation is their coherence time. In this paper we qualitatively describe the role of quasiparticles in decoherence. We discuss two methods

Counting Errors in a Voltage-Biased Electron Pump

April 30, 2003
Author(s)
Xavier Jehl, Mark W. Keller, Richard L. Kautz, Joe Aumentado, John M. Martinis
We have measured the counting errors of a 7-junction electron pump when charge is pumped against a voltage difference. At voltages above about 50 υV, we find that the errors increase exponentially with both pump voltage and temperature, in agreement with

Decoherence of a Superconducting Qubit due to Bias Noise

March 25, 2003
Author(s)
John M. Martinis, Sae Woo Nam, Joe Aumentado, Kristine Lang, C Urbina
We calculate for the current-biased Josephson junction the decoherence of the qubit state from noise and dissipation. The effect of dissipation can be entirely accounted for through a noise model of the current bias that appropriately includes the effect

A Seven Junction Cooper Pair Pump

February 15, 2003
Author(s)
Joe Aumentado, Mark W. Keller, John M. Martinis
We have measured current-voltage curves and individual charge transfer events in single-Cooper-pair pumps. We observe clear charge pumping in units of 2e, but this behavior is accompanied by significant effects from unwanted quasiparticles.

Single-Cooper-Pair Transistors: Requirements for Robust 2e Periodicity

January 3, 2003
Author(s)
Joe Aumentado, Mark W. Keller, John M. Martinis
The superconducting analog of the single-electron transistor (SET), the single-Cooper-pair transistor (SCPT), is comprised of two ultrasmall tunnel junctions in series forming an island (see Figure 1(a)). Transport through the SCPT depends on the

Rabi Oscillations in a Large Josephson Junction Qubit

September 9, 2002
Author(s)
John M. Martinis, Sae Woo Nam, Joe Aumentado, C Urbina
We have designed and operated a circuit based on a large-area current-biased Josephson junction whose two lower energy quantum levels could be used to implement a solid-state qubit. The circuit allows measurement of the qubit states with a fidelity of 85%