Atom-dimer Collisions Research Articles

Ultracold charged atom-dimer collisions: State-selective charge exchange and three-body recombination

Based on an accurate determination of the potential energy surfaces of Rb3+ correlated to its first asymptotic limit Rb++Rb(5s)+Rb(5s), we identify the presence of intersections of a pair of singlet and triplet surfaces over all interparticle distances, leading to Jahn-Teller (JT) couplings. We elaborate scenarios for charge exchange between ultracold charged atom-dimer complex (Rb+Rb2+ or Rb++Rb2), predicting a strong selectivity on the preparation of the initial state of the dimer. We also demonstrate that the JT couplings must drive the three-body recombination (TBR) of Rb+, Rb, and Rb at ultracold energies. Using the current analysis, we provide a consistent picture of the TBR experiments performed in ion-atom hybrid Rb samples. We also demonstrate the presence of JT coupling as a general phenomenon in the singly charged homonuclear alkali triatomic systems. Published by the American Physical Society 2024

Collisional Loss of One-Dimensional Fermions Near a p-Wave Feshbach Resonance.

We study collisional loss of a quasi-one-dimensional spin-polarized Fermi gas near a p-wave Feshbach resonance in ultracold ^{6}Li atoms. We measure the location of the p-wave resonance in quasi-1D and observe a confinement-induced shift and broadening. We find that the three-body loss coefficient L_{3} as a function of the quasi-1D confinement has little dependence on confinement strength. We also analyze the atom loss with a two-step cascade three-body loss model in which weakly bound dimers are formed prior to their loss arising from atom-dimer collisions. Our data are consistent with this model. We also find a possible suppression in the rate of dimer relaxation with strong quasi-1D confinement. We discuss the implications of these measurements for observing p-wave pairing in quasi-1D.

Observation of Efimov Molecules Created from a Resonantly Interacting Bose Gas

We convert a strongly interacting ultracold Bose gas into a mixture of atoms and molecules by sweeping the interactions from resonant to weak. By analyzing the decay dynamics of the molecular gas, we show that in addition to Feshbach dimers it contains Efimov trimers. Typically around 8% of the total atomic population is bound into trimers, identified by their density-independent lifetime of about 100 μs. The lifetime of the Feshbach dimers shows a density dependence due to inelastic atom-dimer collisions, in agreement with theoretical calculations. We also vary the density of the gas across a factor of 250 and investigate the corresponding atom loss rate at the interaction resonance.

Atom-dimer and dimer-dimer scattering in fermionic mixtures near a narrow Feshbach resonance

We develop a diagrammatic approach for solving few-body problems in heteronuclear fermionic mixtures near a narrow interspecies Feshbach resonance. We calculate s-, p-, and d-wave phaseshifts for the scattering of an atom by a weakly-bound dimer. The fermionic statistics of atoms and the composite nature of the dimer lead to a strong angular momentum dependence of the atom-dimer interaction, which manifests itself in a peculiar interference of the scattered s- and p-waves. This effect strengthens with the mass ratio and is remarkably pronounced in 40K-(40K-6Li) atom-dimer collisions. We calculate the scattering length for two dimers formed near a narrow interspecies resonance. Finally, we discuss the collisional relaxation of the dimers to deeply bound states and evaluate the corresponding rate constant as a function of the detuning and collision energy.

Atom-Dimer Scattering in a Three-Component Fermi Gas

Ultracold gases of three distinguishable particles with large scattering lengths are expected to show rich few-body physics related to the Efimov effect. We have created three different mixtures of ultracold 6Li atoms and weakly bound 6Li2 dimers consisting of atoms in three different hyperfine states and studied their inelastic decay via atom-dimer collisions. We have found resonant enhancement of the decay due to the crossing of Efimov-like trimer states with the atom-dimer continuum in one mixture as well as minima of the decay in another mixture, which we interpret as a suppression of exchange reactions of the type |12+|3→|23+|1. Such a suppression is caused by interference between different decay paths and demonstrates the possibility of using Efimov physics to control the rate constants for molecular exchange reactions in the ultracold regime.

Formula for the Transition Probability Induced by Long-range Potential Terms Varying as R-8 and R-10 for Atom-dimer Collisions

Abstract An explicit formula is derived for the transition probability between two different states of the atom-dimer collisional system governed by second-order long-range interaction potential terms varying as R-8 and R-10.

Energy transfer in atom-dimer collisions.

Energy transfer in atom-dimer collisions is analyzed using a model of loosely bound hard spheres. The results are compared with calculations for a real system. It is found that large energy transfer at a particular scattering angle is sensitive to the initial internal state of the dimer. A quantum theory of atom-dimer collisions is developed and it is found that resonances in the dissociation channel of the dimer are expected. The final rotational states of the dimer are also investigated. It is found that large energy transfer occurs with no change in the rotational state of the dimer.

Trajectory study of the formation and decay of silicon trimer complexes in monomer–dimer collisions

The dynamics of the formation and dissociation of Si3 complexes in atom–dimer collisions have been investigated using quasiclassical trajectories on a potential-energy surface that is a global fit to the available experimental data and ab initio CI and MP4 results. The fitted surface yields excellent results for the equilibrium geometries of both Si2 and Si3. The rms deviation of the energies from the MP4 calculations is 0.117 eV. The Si3 fundamental frequencies agree with the MP4 results to within 37 cm−1 or less. Formation cross sections for Si3 formation are reported as a function of initial relative translational energy. These cross sections are found to exhibit a near double exponential dependence upon relative translational energy. The thermal rate coefficients are on the order of 1015 cm3/mol s and show a negative temperature dependence at temperatures below 200 K. Microcanonical dissociation rate coefficients for Si3 complexes are reported for six different internal Si3 energies. These values follow an RRK energy dependence with s=2.67. The average Si3 lifetimes are found to lie in the range 4.71×10−13−5.02×10−11 s.