Perturbation-assisted Observation of the Lowest Vibrational Level of the $\mathrm{b}^{3}\Pi_{0}$ State of Ultracold LiK Molecules

TL;DR

This study reports the first spectroscopic observation of the lowest vibrational level of the $ ext{b}^{3}\Pi_{0}$ state in ultracold LiK molecules, providing essential data for quantum applications involving long coherence times.

Contribution

The paper presents the first experimental detection and detailed spectroscopic characterization of the $ ext{b}^{3}\Pi_{0}$ state in $^{6} ext{Li}^{40} ext{K}$ molecules, including transition frequency and rotational constants.

Findings

Transition frequency determined at 314,230.5 GHz.

Rotational constant of $h\times8.576$ GHz measured.

Energy separation between states calculated as $hc\times10,481.03$ cm$^{-1}$.

Abstract

The narrow transition from the lowest rovibrational level of the $\mathrm{X}^{1}\Sigma^{+}$ electronic ground state to the lowest vibrational level of the $\mathrm{b}^{3}\Pi_{0}$ potential provides opportunities for achieving magic-wavelength trapping of ultracold bialkali molecules for enhancing their rotational coherence times. Guided by existing spectroscopic data of several perturbed and deeply-bound rovibrational states of the $\mathrm{A}^{1}\Sigma^{+}$ potential [Grochola et al., Chem. Phys. Lett., 2012, 535, 17-20], we conducted a targeted spectroscopic search and report the first observation of the lowest vibrational level of the $\mathrm{b}^{3}\Pi_{0}$ state in $^{6}\mathrm{Li}^{40}\mathrm{K}$. The transition frequency from $|\mathrm{X}^{1}\Sigma^{+},\,v=0,\,J=0>$ to $|\mathrm{b}^{3}\Pi_{0},\,v'=0,\,J'=1>$ is determined to be 314,230.5(5)GHz. Assisted by microwave spectroscopy, we resolved the rotational structure of $|\mathrm{b}^{3}\Pi_{0},\,v'=0>$ and extracted a rotational constant of $h\times8.576(44)$ GHz for the $\mathrm{b}^{3}\Pi_{0}$ state. From this, we deducted an energy separation between $|\mathrm{b}^{3}\Pi_{0},v'=0,J'=0>$ and $|\mathrm{X}^{1}\Sigma^{+},v=0,J=0>$ of $hc\times$10,481.03(2) $\mathrm{cm}^{-1}$. Our work provides timely and precise information on the deeply-bound region of the $\mathrm{b}^{3}\Pi_{0}$ triplet excited potential of LiK, and benefits future applications of ultracold LiK isotopologues in quantum simulation and quantum computation that demand long coherence times.