  Quantum rotors promise unique advantages for quantum sensing, quantum
simulation, and quantum information processing. At present, a variety of
systems ranging from nanoparticles to single molecules and trapped ions have
demonstrated detection and control of rotational motion in and near the quantum
regime. For future applications of quantum rotors, understanding their dynamics
in the presence of ambient environments and decoherence will be critical. While
other model quantum systems such as the harmonic oscillator have seen extensive
experimental study of their decoherence dynamics, such experiments remain an
open task for the rigid rotor. We present measurements of fundamental scaling
relationships for decoherence of a quantum planar rotor realized with two
trapped ions, and find excellent agreement with recent theoretical work.
