# Observation of interference between resonant and detuned STIRAP in the adiabatic creation of $^{23}$Na$^{40}$K molecules

## TL;DR

This paper reports the first observation of interference between resonant and detuned STIRAP in creating $^{23}$Na$^{40}$K molecules, revealing complex quantum dynamics and coherence effects in molecular state preparation.

## Contribution

It demonstrates the coexistence and interference of resonant and detuned STIRAP in molecular creation, challenging the assumption that detuned STIRAP can be neglected.

## Key findings

- Interference causes oscillations in Feshbach molecule numbers with ~90% visibility.
- Interference occurs despite large detuning and well-resolved intermediate states.
- Hyperfine levels are coherently superposed, not incoherent mixtures.

## Abstract

Stimulated Raman adiabatic passage (STIRAP) allows to efficiently transferring the populations between two discrete quantum states and has been used to prepare molecules in their rovibrational ground state. In realistic molecules, a well-resolved intermediate state is usually selected to implement the resonant STIRAP. Due to the complex molecular level structures, the detuned STIRAP always coexists with the resonant STIRAP and may cause unexpected interference phenomenon. However, it is generally accepted that the detuned STIRAP can be neglected if compared with the resonant STIRAP. Here we report on the first observation of interference between the resonant and detuned STIRAP in the adiabatic creation of $^{23}$Na$^{40}$K ground-state molecules. The interference is identified by observing that the number of Feshbach molecules after a round-trip STIRAP oscillates as a function of the hold time, with a visibility of about 90\%. This occurs even if the intermediate excited states are well resolved, and the single-photon detuning of the detuned STIRAP is about one order of magnitude larger than the linewidth of the excited state and the Rabi frequencies of the STIRAP lasers. Moreover, the observed interference indicates that if more than one hyperfine level of the ground state is populated, the STIRAP prepares a coherent superposition state among them, but not an incoherent mixed state. Further, the purity of the hyperfine levels of the created ground state can be quantitatively determined by the visibility of the oscillation.