Ultracold, radiative charge transfer in hybrid Yb ion–Rb atom traps

Abstract

Ultracold hybrid ion-atom traps offer the possibility of microscopic manipulation of quantum coherences in the gas using the ion as a probe. However, inelastic processes, particularly charge transfer can be a significant process of ion loss and has been measured experimentally for the Yb + ion immersed in a Rb vapour. We use first-principles quantum chemistry codes to obtain the potential energy curves and dipole moments for the lowest-lying energy states of this complex. Calculations for the radiative decay processes cross sections and rate coefficients are presented for the total decay processes; Yb + (6s 2 S) + Rb (5s 2 S) → Yb(6s 2 1 S) + Rb + (4p 6 1 S) + hν and Yb + (6s 2 S) + Rb(5s 2 S) → YbRb + (X 1 Σ + ) + hν. Comparing the semi-classical Langevin approximation with the quantum approach, we find it provides a very good estimate of the background at higher energies. The results demonstrate that radiative decay mechanisms are important over the energy and temperature region considered. In fact, the Langevin process of ion-atom collisions dominates cold ion-atom collisions. For spin-dependent processes [1] the anisotropic magnetic dipole-dipole interaction and the second-order spin-orbit coupling can play important roles, inducing coupling between the spin and the orbital motion. They measured the spin-relaxing collision rate to be approximately 5 orders of magnitude higher than the charge-exchange collision rate [1].Regarding the measured radiative charge transfer collision rate, we find that our calculation is in very good agreement with experiment and with previous calculations. Nonetheless, we find no broad resonances features that might underly a strong isotope effect. In conclusion, we find, in agreement with previous theory that the isotope anomaly observed in experiment remains an open question. arXiv:1404.6579v1 [physics.atom-ph] 25 Apr 2014 J = 0 J = 1 J = 2 J = 3 J = 4 J = 5 J = 6 J = 7 J = 8 J = 9 Total, multipole Total, dipole

Formation of molecular ions by radiative association of cold trapped atoms and ions

“…As for the Rb-Yb + system, the experimental rates measured in [23] are 3 ± × − 1 10 14 cm 3 s −1 and 4.5 ± × − 1.5 10 14 cm 3 s −1 , corresponding to the 172 Yb + and the 174 Yb + isotope, respectively, and when Rb is prepared in the (F = 2, = M 2 F ) hyperfine level (F being the total angular momentum including nuclear spin and M F its projection on the magnetic field axis used for the preparation). The present computed rate as well as those of [67,74] are thus in remarkable agreement within the error bars with the experimental results. It is noteworthy to quote that the same experimental group later discovered a huge effect of the initial preparation of the Rb atoms in a given hyperfine level, with a rate 35 times larger than the above one when Rb is in the (F = 1, = M 1 F ) hyperfine level [26].…”

“…Our values for R e and D e of the X PEC are in good agreement with those of [67], while the potential well depth from [66,74] is twice smaller than ours, with a minimum located at a significantly larger distance. This has been quoted by the authors of [74] but no explanation has been provided. On the other hand for the A state, the three previous papers have obtained results in good agreement among each other, while we find an equilibrium distance shorter by about 1 a.u.…”

“…The remarkably close values of these rates along the species is well understood from the similarities of their electronic structure invoked earlier, while their differences play only a minor role. This is exemplified by the results from [67,74] of 2.9× − 10 14 cm 3 s −1 for the RA + RCT rate in RbYb + , where the large difference of the A potential well compared to the present one only slightly influences the final rate, as the main contribution is controlled by the inner classical turning point of the PEC. The magnitude of the present rates is also consistent with the smaller theoretical rate of 1.5× − 10 15 cm 3 s −1 computed for the same processes in Ca-Yb + mixture [39], as the energy difference δ − R X A t between the inner classical turning point of the A Σ + inducing NRCT which is predicted to dominate the dynamics of the charge exchange process.…”

“…As already quoted above, the cases of RbYb + and LiYb + are peculiar, as the Yb + ion and Yb atom have not been treated with a large ECP before. Tables 1 and 2 reveal a contrasted situation for RbYb + in comparison with the results of [66,67,74] that are all obtained with similar approaches based on small core ECPs. Our values for R e and D e of the X PEC are in good agreement with those of [67], while the potential well depth from [66,74] is twice smaller than ours, with a minimum located at a significantly larger distance.…”

Measurement of the low-energyNa+−Natotal collision rate in an ion-neutral hybrid trap

“…Recently, a hybrid trap was developed that also incorporates an optical cavity [9]. Over the past decade, since the hybrid trap was originally proposed [10,11], both experimental [2,[4][5][6][7][8][9][12][13][14][15][16][17][18][19][20][21][22] and theoretical [23][24][25][26][27][28][29][30] interest in low-energy ion-neutral collisions has surged.…”