  We demonstrate the use of a single trapped ion as a sensor to probe
electric-field noise from interchangeable test surfaces. As proof of principle,
we measure the magnitude and distance dependence of electric-field noise from
two ion-trap-like samples with patterned Au electrodes. This trapped-ion sensor
could be combined with other surface characterization tools to help elucidate
the mechanisms that give rise to electric-field noise from ion-trap surfaces.
Such noise presents a significant hurdle for performing large-scale trapped-ion
quantum computations.
