Perturbation-assisted Observation of the Lowest Vibrational Level of the ${\mathrm{b}}^3{\hat{I}}_0$ State of Ultracold LiK Molecules

Abstract

The narrow transition from the lowest rovibrational level of the ${\mathrm{X}}^1\hat{I}{\pounds }^{+}$ electronic ground state to the lowest vibrational level of the ${\mathrm{b}}^3{\hat{I}}_0$ 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 ${\mathrm{A}}^1\hat{I}{\pounds }^{+}$ 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 ${\mathrm{b}}^3{\hat{I}}_0$ state in ${}^6{\mathrm{Li}}^{40}\mathrm{K}$. The transition frequency from $|{\mathrm{X}}^1\hat{I}{\pounds }^{+},v=0,J=0>$ to $|{\mathrm{b}}^3{\hat{I}}_0,v^{\prime }=0,J^{\prime }=1>$ is determined to be 314,230.5(5)GHz. Assisted by microwave spectroscopy, we resolved the rotational structure of $|{\mathrm{b}}^3{\hat{I}}_0,v^{\prime }=0>$ and extracted a rotational constant of $h\times 8.576(44)$ GHz for the ${\mathrm{b}}^3{\hat{I}}_0$ state. From this, we deducted an energy separation between $|{\mathrm{b}}^3{\hat{I}}_0,v^{\prime }=0,J^{\prime }=0>$ and $|{\mathrm{X}}^1\hat{I}{\pounds }^{+},v=0,J=0>$ of $hc\times$10,481.03(2) ${\mathrm{cm}}^{-1}$. Our work provides timely and precise information on the deeply-bound region of the ${\mathrm{b}}^3{\hat{I}}_0$ triplet excited potential of LiK, and benefits future applications of ultracold LiK isotopologues in quantum simulation and quantum computation that demand long coherence times.