State purity of decelerated molecular beams

Abstract Cold, velocity-controlled molecular beams consisting of a single quantum state are a powerful tool for exploring molecular interactions. Here, we explore the state purity and resulting dynamics of a Stark-decelerated beam of ammonia molecules where numerous rotational states are initially populated. Under these circumstances, Stark deceleration is shown to be ineffective at producing a molecular beam consisting of a single quantum state. Therefore, quantum state purity must be carefully considered when using Stark decelerated beams and analogous techniques, particularly in collision experiments where contributions from all quantum states must be addressed.