The ion microscope research team at the 5th Institute of Physics at the University of Stuttgart has successfully investigated dynamic processes of atomic collisions under extreme conditions by using a unique high-resolution ion microscope. They were able to predict complex particle movements and to measure them in experiments. Their discovery contributes to a deeper understanding of how collision dynamics arise in quantum mechanical systems.
Ions and Rydberg atoms on collision course
The researchers are exploiting the special properties of ions and Rydberg atoms, which can both interact with each other over very large distances. Here, the two particles attract each other, although only the ion has a positive charge, while the Rydberg atom is neutral. The high degree of control of the experimental parameters makes it possible to control the initial conditions – like the distance between the two particles – with high precision.
A peculiar property of the investigated collision is that the two particles can collide not only in a single way, but on many different collision channels. Transitions between individual collision paths can occur at the points, where two collision channels cross each other. The researchers have calculated a map of all relevant collision paths and the positions of their crossings. At each crossing, a particle either remains on its original path or hops to a different quantum mechanical state, i.e., changes to an alternative channel. Such quantum state transitions also play an important role in a large variety of other systems, whenever two interacting quantum mechanical states cross.
The system based on an ion-Rydberg pair has the advantage that the particles, which are on a collision course, are relatively far apart. Therefore, the collision process is relatively slow and can be observed quite well. Another interesting detail is that particles moving quickly toward each other collide at a later point in time compared to particles that were travelling initially more slowly. This counterintuitive behavior is explained by the avoided crossings in the system: the probability for a particle to hop to another collision channel is greater if it is moving slowly. As all particles are initially prepared on the slowest collisional channel, each hopping event leads to a speed-up in the collision dynamics. This effect is observable as a clear decrease in the time it takes for the two particles to collide.
Furthermore, the scientists were not only able to observe this phenomenon, but also to manipulate the hopping probabilities in a controlled manner. Together with a team from the University of Hamburg, the researchers have developed a mathematical model to simulate these complex collision processes. The results of the theoretical model agree very well with the observations made in the experiment.
Outlook
The detailed observation and simulation of collision processes at the atomic level allows the precise prediction of particle behavior. The developed mathematical model can be easily applied to many other physical systems, for example in the field of cold quantum chemistry or for the description of ionization processes of atoms and molecules.
Original publication
Moritz Berngruber, Daniel J. Bosworth, Oscar A. Herrera-Sancho, Viraatt S. V. Anasuri, Nico Zuber, Frederic Hummel, Jennifer Krauter, Florian Meinert, Robert Löw, Peter Schmelcher, Tilman Pfau
‚In Situ Observation of Nonpolar to Strongly Polar Atom-Ion Collision Dynamics‘
Phys. Rev. Lett. 133, 083001 (2024)
arXiv:2401.12312 [physics.atom-ph], https://doi.org/10.48550/arXiv.2401.12312 (2024)
