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Our group studies chemical processes from a theoretical perspective involving atoms, molecules, ions, and Rydbergs at very low temperatures (below 1K). At these low temperatures, quantum mechanical effects may dominate the dynamics, and new possibilities of control of reactions emerge. Our approach to the different processes is based on a theoretical study and development of appropriate models followed by simulations to compare our predictions against experimental results. 

Few-body physics in cold atom-ion hybrid systems

The development of hybrid trap technologies for simultaneous cooling and trapping of atoms and ions has brought about the possibility of studying chemical reactions between charged and neutral particles with significant control over the internal states of the collisional partners. This hybrid technology is appropriate for studying ion-neutral collisional processes down to temperatures of a few mK. Interestingly, pure many-body quantal effects may emerge, such as forming a mesoscopic ion, or polarons, when an ion is viewed as an impurity in the bath of atoms. However, ions are highly reactive, presenting diverse reaction pathways: radiative association, charge-exchange reactions, or ion-atom-atom three-body recombination, compromising some of the expected many-body features of this system. Moreover, ion-atom-atom three-body recombination leads to the formation of weakly bound molecular ions that turns out to be the tip of the iceberg of acomplex reaction network.  

Phase-diagram of a charged impurity in a bath of molecules

3bodyphasediagram

Ion-atom-atom three-body recombination              

In our group, from a theoretical approach, we study few-body processes involving charged and neutral colliding partners like ion-atom-atom three-body recombination. In particular, we develop new strategies to treat this process and understand how it behaves as a function of the system's temperature, thus, overlapping with the research in cold plasma physics. In addition, we want to understand how the reactivity of an ion changes as the environment is modified. For instance, what happens if one has a molecular one instead of an atomic bath? We have explored some avenues, but still, there is much to be done. In addition, we study molecular ions' vibrational and rotational relaxation mechanisms in the presence of a buffer gas or ultracold atomic gas. In most of these applications, although, at low temperatures, many partial waves play a role in the scattering owing to the solid charged-neutral long-range interaction. These problems are treated mainly from a classical approach due to many partial waves relevant for ion-neutral diffusion at low temperatures. In addition, we are interested in studying the role of the trapping fields on the dynamics of ions, molecular ions, and the different reaction pathways. 


Ultracold chemistry

Ultracold chemistry deals with chemical processes at temperatures below 1mK in which only a few partial waves contribute to the scattering. As a result, chemical reactions are entirely determined by quantum mechanical effects that can be further exploited to tailor and control the reaction product's formation. Motivated by such applications, laser cooling of molecules is becoming a popular way to achieve ultracold molecules in contrast to indirect cooling techniques used in bi-alkali systems. However, identifying suitable candidates for molecular laser cooling is not straightforward. Moreover, it is sometimes full of surprises, thus making the topic very challenging and exciting. In our group, we perform ab initio quantum chemistry calculations towards elucidating good candidates for laser cooling. Similarly, we apply inversion techniques to get real potential curves from spectroscopic data. On the other hand, we follow a data-driven approach to expedite our sampling capabilities and identify the best candidates.

lasercoolingLaser cooling scheme for AlF

However, the final number of attainable ultracold molecules depends on having a proper source: a controllable manner to create an intense and slow molecular beam prior to laser cooling. In general, molecules are created in a buffer gas source after the ablation of a given material in a particular atmosphere. In our group, we study the chemical reaction network of the ablated material in a given atmosphere and identify the most relevant reaction pathways. Our approach is based on on-the-fly molecular dynamics simulations over potential energy surfaces calculated at high level electronic structure methods. As a result, we identify the best combination of material and atmosphere, leading to slow molecules' most effective formation rate. 

                         NF3 + Al -> NF2 + AlF reaction relevant for the formation of AlF molecules in a buffer gas cell.

Our group is interested in exploiting the strong light-matter coupling paradigm to manipulate and control light-assisted chemical reactions in the ultracold regime, such as photoassociation. In the same vein, we explore coherent control approaches to photoassociation reactions. However, our approach selects the reactant states to lead to the desired product state. Similarly, we are interested in understanding energy exchange mechanisms in atom-molecule and molecule-molecule ultracold collisions. These affect the possibilities of reaching a molecular Bose-Einstein condensate.  

photonics

Photoassociation scheme of ultracold molecules near a nanophotonic crystal


Rydberg physics

Rydberg physics is a classic in the atomic community. Surprisingly enough, still, it is a theme in vogue, owing to the promising applications of Rydberg atoms in quantum information systems and the recent observations of ultra-long-range Rydberg molecules. Ultra-long-Rydberg molecules appear when a Rydberg atom is immersed in a high-density ultracold gas, generally a Bose-Einstein condensate. These molecules are studied from a many-body or atomic physics approach. However, in most approaches, the stability of these molecules is not studied. In our group, we investigate the different chemical processes that induce the decay of these molecules and hence define the lifetime of such exotic molecular bound. Additionally, we explore As relevant atom-Rydberg and Rydberg-ion scattering processes that play a role in the stability of Rydberg-atom and Rydberg-ion systems.

                     Potential energy curves relevant for chemi-ionization.

Rydberg


IonRydberg

   Appropriate treatment for  ion-Rydberg collisions

 

Relevant publications

M. Mirahmadi and J. Pérez-Ríos
Ion-atom-atom three-body recombination: from the cold to the thermal regime 
 
X. Liu, W, Wang, S. C. Wright, M. Doppelabauer, S. Truppe, G. Meijer and J. Pérez-Ríos
The chemistry of AlF and CaF production in buffer gas sources
 
M. Londoño-Castellanos, J. Madroñero and J. Pérez-Ríos
A single ion in a high-density medium: a stochastic approach
 
H. Hirzler, R. S. Lous, E. Trimby, J. Pérez-Ríos, A. Safavi-Naini and R. Gerritsma
Observation of Chemical Reactions between a Trapped ion an ultracold Feshbach Dimers
Phys. Rev. Lett 128, 103401 (2022)
 
M. Karra, M. T. Cretu, B. Friedrich, S. Truppe, G. Meijer  and J. Pérez-Ríos
Dynamics of translational and rotational thermalization of AlF molecules via collisions with cryogenic helium  
Phys. Rev. A 105, 022808 (2022)
 
Henrik Hirzler and Jesús Pérez-Ríos
Rydberg atom-ion collisions in cold environments
Phys. Rev. A 103, 043323 (2021)
 
Jesús Pérez-Ríos
Cold chemistry: a few-body perspective on impurity physics of a single ion in an ultracold bath
Mol. Phys. e1881637 (2021)
 
Amir Mohammadi, Artjom Krükow, Amir Mahdian, Markus Deiß, Jesús Pérez-Ríos, Humberto da Silva, Jr., Maurice Raoult, Olivier Dulieu and Johannes Hecker Denschlag
Life and death of a cold BaRb+ molecule inside an ultracold cloud of Rb atoms
Phys. Rev. Research 3, 013196 (2021)
 
Jesús Pérez Ríos
Vibrational quenching and reactive processes of weakly bound molecular ions colliding with atoms at cold temperatures
Physical Review A 99, 022707 (2019)
 
Jesús Pérez Ríos and Chris H. Greene
Universal temperature dependence of the ion-neutral-neutral three-body recombination rate
Phys. Rev. A 98, 062707 (2018)
 
Jesús Pérez-Ríos, May E. Kim and Chen-Lung Hung
Ultracold molecule assembly with photonic crystals
New J. Phys. 19, 123035 (2017) 
 
Thomas Niederprüm, Oliver Thomas, Tanita Eichert, Carsten Lippe, Jesús Pérez-Ríos, Chris H. Greene and Herwig Ott
Observation of pendular butterfly Rydberg molecules
Nature Communications 7, 12820 (2016)
 
Artjom Krükow, Amir Mohammadi, Arne Härter, Johannes Hecker Denschlag, Jesús Pérez-Ríos, and Chris H. Greene
Energy Scaling of Cold Atom-Atom-Ion Three-Body Recombination
Phys. Rev. Lett 116, 193201 (2016)
 
Michael Schlagmüller, Tara Cubel Liebisch, Felix Engel, Kathrin S. Kleinbach, Fabian Böttcher, Udo Hermann, Karl M. Westphal, Anita Gaj, Robert Löw, Sebastian Hofferberth, Tilman Pfau, Jesús Pérez-Ríos, and Chris H. Greene
Ultracold Chemical Reactions of a Single Rydberg Atom in a Dense Gas
Phys. Rev. X 6, 031020 (2016)