Full-dimensional quantum scattering calculations on ultracold atom-molecule collisions in magnetic fields: The role of molecular vibrations

Masato Morita,Jacek Kłos,Timur V Tscherbul

doi:10.1103/physrevresearch.2.043294

Masato Morita, Jacek Kłos + Show 1 more

Open Access

https://doi.org/10.1103/physrevresearch.2.043294

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Abstract

Rigorous quantum scattering calculations on ultracold molecular collisions in external fields present an outstanding computational problem due to strongly anisotropic atom-molecule interactions that depend on the relative orientation of the collision partners, as well as on their vibrational degrees of freedom. Here, we present the first numerically exact three-dimensional quantum scattering calculations on strongly anisotropic atom-molecule (Li+CaH) collisions in an external magnetic field based on the parity-adapted total angular momentum representation and a new three-dimensional potential energy surface (PES) for the triplet Li-CaH collision complex using the unrestricted coupled cluster method with single, double and perturbative triple excitations [UCCSD(T)] and a large quadruple-zeta type basis set. We find that while the full three-dimensional treatment is necessary for the accurate description of Li ($M_S=1/2$)+CaH ($v=0,N=0,M_S=1/2$) collisions as a function of magnetic field, the magnetic resonance density and statistical properties of spin-polarized atom-molecule collisions are not strongly affected by vibrational degrees of freedom, justifying the rigid-rotor approximation used in previous calculations. We observe rapid, field-insensitive vibrational quenching in ultracold Li ($M_S=1/2$)+CaH ($v=1,N=0, M_S=1/2$) collisions, leading to efficient collisional cooling of CaH vibrations.

Highlights

The quantum dynamics of ultracold molecular collisions is a focal point of several major avenues of research within the emerging field of ultracold molecular gases [1,2]
We note that basis-set convergence is not required when one is interested in quantities averaged over an ensemble of potential energy surfaces (PESs), such as the cumulative probability distributions [24] examined in Sec
We have recently developed a probabilistic approach to this problem based on cumulative probability distributions (CPDs) obtained by averaging scattering observables over an ensemble of slightly different interaction PESs [24]

Summary

INTRODUCTION

The quantum dynamics of ultracold molecular collisions is a focal point of several major avenues of research within the emerging field of ultracold molecular gases [1,2]. Sympathetic cooling has been observed experimentally in a trapped mixture of NaLi(a3 +) molecules with Na(2S) atoms [20] These experimental advances strongly motivate rigorous, full-dimensional quantum dynamical calculations on ultracold molecular collisions in the presence of external magnetic fields. Previous theoretical work has explored the effects of molecular vibrations on ultracold atom-molecule collisions in the absence of external fields using converged CC quantum scattering calculations. We employ the computationally efficient total angular momentum basis [25] and make explicit use of inversion symmetry to minimize the number of CC basis states These improvements allow us to achieve numerical convergence of Li + CaH scattering observables using extended rovibrational basis sets including up to 14 vibrational and 56 rotational states of CaH.

Ab initio interaction PES

Quantum scattering theory and computational methodology

Vibrational basis-set convergence

Sensitivity to the interaction potential

SUMMARY