Robust coherent control of collisions in and beyond the ultracold regime

When particles (atoms, ions, or molecules) collide in a superposition of their internal states, different pathways are created that interfere with one another. By tuning the relative phases of the superposition, the interference contribution can be manipulated, resulting in coherent control of the scattering properties, such as differential/integral cross-section and the reaction rates. Unfortunately, the interference contributions of different partial waves are generally random and tend to cancel one another. The ultracold regime mitigates this issue, involving only a few initial and final partial waves. However, the possibilities of coherent control beyond the ultracold regime remain largely unexplored. We have recently identified one such possibility based on the partial wave phase-locking mechanism, in which robust control is no longer limited by the partial wave expansion and can therefore be achieved at much higher collision energies than previously thought possible. We will exemplify this strategy by showing robust coherent control of Rb-Sr+ collisions. We will also discuss how coherent control could be used as a method to probe subtle details of scattering dynamics such as the partial wave phase-locking mechanism or the phase of the S-matrix.