Quantum spin state selectivity and magnetic tuning of ultracold chemical reactions of triplet alkali-metal dimers with alkali-metal atoms

TL;DR

This study shows how ultracold chemical reactions involving alkali-metal atoms and triplet alkali-metal dimers can be controlled using hyperfine states and magnetic fields, revealing significant reaction rate sensitivities and suppression mechanisms.

Contribution

It introduces a method to manipulate ultracold reactions via hyperfine state selection and magnetic Feshbach resonances, supported by coupled-channel calculations including hyperfine and Zeeman effects.

Findings

Reaction rates depend on initial hyperfine states.

Spin polarization suppresses reaction by 10-100 times.

Magnetic Feshbach resonances can alter reaction rates by orders of magnitude.

Abstract

We demonstrate that it is possible to efficiently control ultracold chemical reactions of alkali-metal atoms colliding with open-shell alkali-metal dimers in their metastable triplet states by choosing the internal hyperfine and rovibrational states of the reactants as well as by inducing magnetic Feshbach resonances with an external magnetic field. We base these conclusions on coupled-channel statistical calculations that include the effects of hyperfine contact and magnetic-field-induced Zeeman interactions on ultracold chemical reactions of hyperfine-resolved ground-state Na and the triplet NaLi(a$^3\Sigma^+$) producing singlet Na$_2$($^1\Sigma^+_g$) and a Li atom. We find that the reaction rates are sensitive to the initial hyperfine states of the reactants. The chemical reaction of fully spin-polarized, high-spin states of rotationless NaLi(a$^3\Sigma^+, v = 0, N = 0$) molecules with fully spin-polarized Na is suppressed by a factor of 10-100 compared to that of unpolarized reactants. We interpret these findings within the adiabatic state model, which treats the reaction as a sequence of nonadiabatic transitions between the initial non-reactive high-spin state and the final low-spin states of the reaction complex. In addition, we show that magnetic Feshbach resonances can similarly change reaction rate coefficients by several orders of magnitude. Some of these resonances are due to resonant trimer bound states dissociating to the $N=2$ rotational state of NaLi(a$^3\Sigma^+, v = 0$) and would thus exist in systems without hyperfine interactions.