The collision dynamics in hybrid cold atom-ion systems is governed not only by short-range interactions in free space, but also by the time-dependent radio-frequency (RF) field of the linear Paul trap. The recently proposed picture of trap-assisted ion-atom transient complexes suggests that the RF trapping potential can modify the number of short-range ion-atom encounters and the probability of inelastic decay through energy and momentum exchange. In this work, based on a multispecies rubidium ion-cold rubidium atom hybrid trap, we prepare a multispecies ion cloud containing both atomic and molecular ions by continuous photoionization of cold ^87\mathrmRb atoms. We investigate the influence of the RF field on the collision dynamics in two complementary experimental configurations: one in which the system enters the cooperatively confined extended stability region of the linear Paul trap under a single RF field, and the other in which a weak auxiliary RF field is introduced while the main RF field is kept fixed.
In the single-RF configuration, the ion-trap RF frequency is reduced beyond the conventional single-species stability region. The multispecies ion cloud remains observable owing to cooperative confinement, and the apparent ion-atom total-collision-rate coefficient is extracted from the time evolution of the atom and ion numbers using a fixed reference ion-cloud volume. The results show that exothermic inelastic collisions between atomic ions and atoms are enhanced in the low-frequency extended stability region, indicating that the cooperatively confined region beyond the conventional stability boundary provides a new parameter space for studying RF-field-assisted collision dynamics.
In the dual-RF configuration, the main RF field maintains stable confinement, while the weak auxiliary RF field acts as an independent periodic perturbation and scans the sideband region of the atomic ions. The corresponding apparent ion-atom total-collision-rate coefficient shows a nonmonotonic dependence on the auxiliary RF frequency, indicating that the weak auxiliary RF field does not simply enhance collisions, but can modify the ion-cloud evolution and ion-atom collision response in a frequency-selective manner.
Together, these two experimental configurations show that the RF field of a linear Paul trap is not merely a passive confinement background, but can influence multispecies ion-atom collision processes by modifying ion motion, energy-momentum exchange, and the dynamics of trap-assisted ion-atom transient complexes.