# Efficient Pathway to NaCs Ground State Molecules

## TL;DR

This paper explores two-photon pathways to efficiently transfer NaCs molecules from Feshbach states to their rovibrational ground state using spectroscopic analysis and STIRAP, achieving high transfer efficiency for quantum applications.

## Contribution

The study identifies a highly mixed excited state as an optimal bridge for STIRAP, enabling up to 88% transfer efficiency to the NaCs ground state.

## Key findings

- Spectroscopic mapping of over 30 vibrational states.
- Identification of a mixed excited state for efficient transfer.
- Achieved 88% transfer efficiency to the ground state.

## Abstract

We present a study of two-photon pathways for the transfer of NaCs molecules to their rovibrational ground state. Starting from NaCs Feshbach molecules, we perform bound-bound excited state spectroscopy in the wavelength range from 900~nm to 940~nm, covering more than 30 vibrational states of the $c \, ^3\Sigma^+$, $b \, ^3\Pi$, and $B \, ^1\Pi$ electronic states. Analyzing the rotational substructure, we identify the highly mixed $c \, ^3\Sigma^+_1 \, |v=22 \rangle \sim b \, ^3\Pi_1 \, | v=54\rangle$ state as an efficient bridge for stimulated Raman adiabatic passage (STIRAP). We demonstrate transfer into the NaCs ground state with an efficiency of up to 88(4)\%. Highly efficient transfer is critical for the realization of many-body quantum phases of strongly dipolar NaCs molecules and high fidelity detection of single molecules, for example, in spin physics experiments in optical lattices and quantum information experiments in optical tweezer arrays.