Coherent control of cold collisions: role of resonance

Coherent control of collisions uses superpositions of internal states of molecules (or atoms) to create interference effects that can be controlled by varying the relative phase between the states. Unlike current method to control ultracold collisions, this technique is a free-field method, avoiding large perturbations of molecular energy levels. Coherent control is usually limited by cancellation of different partial wave contributions. As shown in one of our previous works, this issue can be overcome for ultracold resonant exchange (spin, charge or excitation exchange) where only a single partial wave is involved in both the incident and final collision channels. For exothermic processes, an isolated resonance provides a solution. We will show that an improvement of control over multiple final channels can be achieved around an isolated resonance for hyperfine de-excitation in Rb-Rb scatterings.



In addition, we will consider collisions that involve a high density of resonances and reach a statistical regime. Although a large extent of control can be achieved when resonances are resolved, energy averaging and the overlap of multiple resonances impacts control.