Access to cold di- and polyatomic molecules could open new research avenues in quantum information science, cold chemistry, precision measurements, etc. A crucial requirement for a molecule to reach cold temperatures via laser cooling is the ability to undergo multiple absorption and emission cycles without dissipation. In contrast to the gas-phase atoms that are amenable to laser-cooling, polyatomic molecules possess additional degrees of freedom that often hamper multiple cycling transitions. Thus, the following three criteria need to be fulfilled for a molecule to be applicable for laser cooling: (1) the existence of a bright electronic transition with a suitable energy, (2) diagonal Franck-Condon factors (FCFs), and (3) the absence of metastable loss states. We use the equation-of-motion coupled-cluster (EOM-CC) methods, which enable robust and accurate treatment of the electronically excited and open-shell systems, to search for polyatomic molecules for laser-cooling applications. We perform calculations on a series of molecules based on the alkali earth metal derivatives with the general chemical formula MR, where M = Ca, Sr, Ba and R is a substituent with varied electron-withdrawing strength, starting from R = H and up to BO<sub>2</sub>, which has the largest known electron affinity. To quantify the extent of electronic excitation, we perform wave-function analysis based on the reduced quantities, such as one-particle reduced transition density matrix and Dyson orbitals. We show that EOM-CC methods together with wave-function analysis tools provide a robust and versatile computational approach for accurate characterization of the electronic structure of molecules with potential applications in laser-cooling.

Optical properties of molecules with cycling centers for quantum information science: Insights from equation-of-motion coupled-cluster theory

2019 Fall National Meeting

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