Rotational Decoherence of a Trapped-Ion Planar Quantum Rotor

Trapped ions have been used to study the decoherence of simple model quantum systems, such as the harmonic oscillator and simple two-level system, in experiments that feature careful control over both the system and the environment under study. The quantum rigid rotor is another simple model quantum system, and in recent years has been the subject of theoretical study, but the resulting predictions have not yet been directly tested by experiment. I will present measurements of the decoherence of a planar quantum rotor, comprised of two trapped ions separated by 6 um. By preparing the rotor in a coherent superposition of angular momentum states and introducing an environment that induces angular momentum diffusion, we find that rotational coherences decay according to a simple scaling law with the distance measure in orientation space, in accordance with the corresponding Markovian master equation.