Excellent Ultracold Molecular Candidates From Group VA Hydrides: Whether Do Nearby Electronic States Interfere?

Donghui Li,Wensheng Bian

doi:10.3389/fchem.2021.778292

Abstract

By means of highly accurate ab initio calculations, we identify two excellent ultracold molecular candidates from group VA hydrides. We find that NH and PH are suitable for the production of ultracold molecules, and the feasibility and advantage of two laser cooling schemes are demonstrated, which involve different spin-orbit states ( and ). The internally contracted multireference configuration interaction method is applied in calculations of the six low-lying Λ-S states of NH and PH with the spin-orbit coupling effects included, and excellent agreement is achieved between the computed and experimental spectroscopic data. We find that the locations of crossing point between the and states of NH and PH are higher than the corresponding v′ = 2 vibrational levels of the state indicating that the crossings with higher electronic states would not affect laser cooling. Meanwhile, the extremely small vibrational branching loss ratios of the → transition for NH and PH (NH: 1.81 × 10–8; PH: 1.08 × 10–6) indicate that the intermediate electronic state will not interfere with the laser cooling. Consequently, we construct feasible laser-cooling schemes for NH and PH using three lasers based on the → transition, which feature highly diagonal vibrational branching ratio (NH: 0.9952; PH: 0.9977), the large number of scattered photons (NH: 1.04×105; PH: 8.32×106) and very short radiative lifetimes (NH: 474 ns; PH: 526 ns). Our work suggests that feasible laser-cooling schemes could be established for a molecular system with extra electronic states close to those chosen for laser-cooling.

Highlights

Searching for promising laser cooling candidates to produce ultracold polar molecules has attracted considerable research interests in recent years owing to their importance for a lot of promising applications in various fields such as precision measurements, quantum computing and quantum information (Hudson et al, 2011; Yan et al, 2013; Baron et al, 2014)
The potential energy curves (PECs) of six Λ-S electronic states of number of scattered photons (NH) and PH are computed with the internally contracted multireference configuration interaction (icMRCI) + Q method
We find that the locations of crossing point between the A3Π and 5Σ− states of NH and PH are higher than the corresponding ]′ 2 vibrational levels of the A3Π state (4,163 and 989 cm−1, respectively) indicating that the crossings with higher electronic states would not affect laser cooling

Summary

Introduction

Searching for promising laser cooling candidates to produce ultracold polar molecules has attracted considerable research interests in recent years owing to their importance for a lot of promising applications in various fields such as precision measurements, quantum computing and quantum information (Hudson et al, 2011; Yan et al, 2013; Baron et al, 2014). Excellent Ultracold Molecular Candidates theoretical efforts have been made to identify more candidates for laser cooling (Wells and Lane, 2011; Fu et al, 2017; Cao et al., 2019; Moussa et al, 2021). It is known (Fu et al, 2016; Yuan et al., 2019; Li et al, 2021) that, a suitable candidate for laser cooling needs to satisfy three criteria: highly diagonal Franck-Condon factors (FCFs), an extremely short radiative lifetime, and no interference from the intermediate electronic states. All electronic states close to those chosen for laser-cooling should be calculated and checked beforehand in selecting laser-cooling candidates

Methods

Results

Conclusion