Dark resonances as a probe for the motional state of a single ion

Abstract

Single, rf-trapped ions find various applications ranging from metrology to quantum computation. High-resolution interrogation of an extremely weak transition under best observation conditions requires an ion almost at rest. To avoid line-broadening effects such as the second-order Doppler effect or rf heating in the absence of laser cooling, excess micromotion has to be eliminated as far as possible. In this paper the motional state of a confined three-level ion is probed, taking advantage of the high sensitivity of observed dark resonances to the trapped ion’s velocity. Excess micromotion is controlled by monitoring the dark-resonance contrast with varying laser-beam geometry. The influence of different parameters such as the cooling laser intensity has been investigated experimentally and numerically.