Controlling the hyperfine state of rovibronic ground-state polar molecules

TL;DR

This paper demonstrates a general method to prepare ultracold polar molecules in a specific hyperfine state within their rovibronic ground state, enabling precise quantum control for future experiments.

Contribution

It introduces a novel scheme using microwave transitions and nuclear quadrupole interactions to control hyperfine states of bialkali polar molecules.

Findings

Successfully prepared molecules in a single hyperfine state

Scheme applicable to arbitrary hyperfine superpositions

Enables precise hyperfine state control in ultracold molecular gases

Abstract

Ultracold molecules offer entirely new possibilities for the control of quantum processes due to their rich internal structure. Recently, near quantum degenerate gases of molecules have been prepared in their rovibronic ground state. For future experiments, it is crucial to also control their hyperfine state. Here, we report the preparation of a rovibronic ground state molecular quantum gas in a single hyperfine state and in particular in the absolute lowest quantum state. The demonstrated and presented scheme is general for bialkali polar molecules and allows the preparation of molecules in a single hyperfine state or in an arbitrary coherent superposition of hyperfine states. The scheme relies on electric-dipole, two-photon microwave transitions through rotationally excited states and makes use of electric nuclear quadrupole interactions to transfer molecular population between different hyperfine states.