Hyperfine structure in the microwave spectra of ultracold polar molecules

TL;DR

This paper analyzes the hyperfine structure in microwave spectra of ultracold alkali metal dimers under various fields, providing detailed transition data and insights into spectral behavior relevant for quantum control.

Contribution

It offers the first detailed calculations of hyperfine-resolved microwave spectra for ultracold molecules in combined fields, aiding quantum manipulation techniques.

Findings

Hyperfine splittings vary with electric and magnetic fields.

Narrow avoided crossings occur at specific electric fields.

Combined fields suppress hyperfine spectral complexity.

Abstract

We investigate the microwave spectra of ultracold alkali metal dimers in magnetic, electric and combined fields, taking account of the hyperfine structure due to the nuclear spins. We consider the molecules 41K87Rb and 7Li133Cs, which are the targets of current experiments and demonstrate two extremes of large and small nuclear quadrupole coupling. We calculate the frequencies and intensities of transitions that may be used to transfer ultracold molecules between hyperfine states in a magnetic field, employing different polarizations of microwave radiation. In an electric field, the hyperfine levels display narrow avoided crossings at specific fields that we explain in terms of molecular alignment. The hyperfine splittings that arise in electric fields may hinder individual addressing in schemes to use ultracold molecules in quantum computation, but the structure of the spectra is suppressed in combined fields.