Abstract
Laser cooling of polyatomic molecules to the ultracold regime may enable some new science and technology applications; however, the related study is still at its very early stage. Here, by means of accurate ab initio and dynamical calculations, we identify two new candidate tetratomic molecules that are suitable for laser cooling and demonstrate the feasibility and advantage of two laser cooling schemes that are able to produce ultracold CaCCH and SrCCH molecules. The internally contracted multiconfiguration reference configuration interaction method is applied, and excellent agreement is achieved between the computed and experimental spectroscopic data. We find that the X2Σ1/2 +→A2Π1/2 transitions for both candidates feature diagonal Franck-Condon factors, short radiative lifetimes, and no interference from intermediate electronic states. In addition, the crossings with higher electronic states do not interfere. We further construct feasible laser cooling schemes for CaCCH and SrCCH, each of which allows scattering 104 photons for direct laser cooling. The estimated Doppler temperatures for both CaCCH and SrCCH are on the order of μK.
Highlights
To produce ultracold molecules is important for some promising applications,1–3 such as precision measurements, design of new sensors, quantum information storage, and quantum computing
In 2016, Isaev and Berger calculated Franck-Condon factors (FCFs) for several polyatomic molecules and suggested promising candidates that could possibly be suitable for direct Doppler cooling based on a rational approach outlined by them
Ivanov et al investigated the prospects of laser cooling larger molecules based on their computed FCFs, and their main concern is an alkaline earth metal attached to an aromatic ligand
Summary
To produce ultracold molecules is important for some promising applications, such as precision measurements, design of new sensors, quantum information storage, and quantum computing. It is desirable to extend this to polyatomic molecules, which may enable some new science and technology applications.. Laser cooling of polyatomic molecules is more difficult due to their complex electronic structures. In 2016, Isaev and Berger calculated Franck-Condon factors (FCFs) for several polyatomic molecules and suggested promising candidates that could possibly be suitable for direct Doppler cooling based on a rational approach outlined by them.. There are other polyatomic molecules that have been computationally studied as candidates for laser cooling.. Ivanov et al investigated the prospects of laser cooling larger molecules based on their computed FCFs, and their main concern is an alkaline earth metal attached to an aromatic ligand. In 2016, Isaev and Berger calculated Franck-Condon factors (FCFs) for several polyatomic molecules and suggested promising candidates that could possibly be suitable for direct Doppler cooling based on a rational approach outlined by them. One year later, Kozyryev et al successfully realized laser cooling of a polyatomic molecular gas (or SrOH gas) to the ultracold temperature experimentally, and in 2020, they further laser-cooled YbOH, CaOCH3,15 and CaOH. There are other polyatomic molecules that have been computationally studied as candidates for laser cooling. In particular, Ivanov et al investigated the prospects of laser cooling larger molecules based on their computed FCFs, and their main concern is an alkaline earth metal attached to an aromatic ligand.
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