We use a single-ion electric-field noise sensor in combination with in situ surface treatment and analysis tools, to investigate the relationship between electric-field noise from metal surfaces in vacuum and the composition of the surface. These experiments are performed in a setup that integrates ion trapping capabilities with surface analysis tools. We find that treatment of an aluminum-copper surface with energetic argon ions significantly reduces the level of room-temperature electric-field noise, but the surface does not need to be atomically clean to show noise levels comparable to those of the best cryogenic traps. The noise levels after treatment are low enough to allow fault-tolerant trapped-ion quantum information processing on a microfabricated surface trap at room temperature. © 2014 American Physical Society.

Electric noise from metallic surfaces is a major obstacle towards quantum applications with trapped ions due to motional heating of the ions. Here, we discuss how the same noise source can also lead to pure dephasing of motional quantum states. The mechanism is particularly relevant at small ion-surface distances, thus imposing a constraint on trap miniaturization. By means of a free induction decay experiment, we measure the dephasing time of the motion of a single ion trapped 50 μm above a Cu-Al surface. From the dephasing times we extract the integrated noise below the secular frequency of the ion. We find that none of the most commonly discussed surface noise models for ion traps describes both the observed heating as well as the measured dephasing satisfactorily. Thus, our measurements provide a benchmark for future models for the electric noise emitted by metallic surfaces.