AVS 65th International Symposium & Exhibition
    Materials and Processes for Quantum Computing Focus Topic Monday Sessions
       Session MP+EM+MN+NS-MoM

Paper MP+EM+MN+NS-MoM8
Variations in Surface Dipole-Moment Density with Coverage for C/Au(110) – (2 × 1) and Electroplated Au Ion-trap Electrodes

Monday, October 22, 2018, 10:40 am, Room 203A

Session: Systems and Devices for Quantum Computing I
Presenter: Dustin Hite, National Institute of Standards and Technology (NIST)
Authors: D.A. Hite, National Institute of Standards and Technology (NIST)
K.S. McKay, National Institute of Standards and Technology (NIST)
H.Z. Jooya, ITAMP, Harvard-Smithsonian Center for Astrophysics
E. Kim, University of Nevada, Las Vegas
P.F. Weck, Sandia National Laboratories
H.R. Sadeghpour, ITAMP, Harvard-Smithsonian Center for Astrophysics
D.P. Pappas, National Institute of Standards and Technology (NIST)
Correspondent: Click to Email
Ion traps, designed to test the feasibility of scalable quantum information processing, suffer from excessive electric-field noise that increases strongly as the ion-electrode spacing decreases in progressively smaller traps. This noise couples to the charge of the ions in the trap causing motional heating, which can result in the decoherence of quantum logic gates. This heating can be reduced by orders of magnitude with the use of cryogenic trap electrodes or by in-situ surface cleaning with ion bombardment in traps with room-temperature electrodes. Many experiments over the past two decades have supported theories that model this noise source as being caused by fluctuations in the dipole moments of contaminant adsorbates on the metallic trap electrode surfaces. Gold electrodes are often used to avoid oxidation and other contaminants, nevertheless a thin carbonaceous layer of approximately 3 monolayers (ML) develops on Au, even due to air exposure alone. In this work, we have studied the model system of C/Au(110) – (2 × 1) to understand the mechanisms for the variations in the surface dipole-moment density as a function of the degree of carbon coverage. We have implemented Kelvin probe force microscopy, along with x-ray photoelectron spectroscopy, to determine an average dipole-moment density with increasing carbon coverage, and have compared the results to density functional theory aided by ab-initio molecular dynamics techniques. We find a nearly linear decrease in the work function with a rate of approximately -0.7 eV/ML for sub-monolayer coverages, a regime in which trapped ions have been observed to have a maximum rate of heating. Finally, we compare the results for the model system to those for a microfabricated ion-trap chip with electroplated Au electrodes contaminated with a native hydrocarbon layer incrementally removed by ion bombardment.