Rotational-hyperfine cooling of $^{205}$TlF in a cryogenic beam

TL;DR

This paper presents a protocol to cool the rotational and hyperfine states of TlF molecules in a cryogenic beam, significantly increasing the population in a single sublevel to enhance precision measurements of fundamental symmetries.

Contribution

The authors develop a novel laser and microwave protocol to transfer molecular populations into a single hyperfine state, improving state preparation for fundamental physics experiments.

Findings

Achieved a 20.1-fold increase in population of the target hyperfine sublevel.

Demonstrated effective transfer of population from multiple levels to a single level.

Enhanced the suitability of TlF molecules for symmetry violation measurements.

Abstract

The aim of CeNTREX (Cold Molecule Nuclear Time-Reversal Experiment) is to search for time-reversal symmetry violation in the thallium nucleus, by measuring the Schiff moment of $^{205}$Tl in the polar molecule thallium fluoride (TlF). CeNTREX uses a cryogenic beam of TlF with a rotational temperature of 6.3(2) K. This results in population spread over dozens of rotational and hyperfine sublevels of TlF, while only a single level is useful for the Schiff moment measurement. Here we present a protocol for cooling the rotational and hyperfine degrees of freedom in the CeNTREX beam, transferring the majority of the Boltzmann distribution into a single rotational and hyperfine sublevel by using a single ultraviolet laser and a pair of microwave beams. We achieve a factor of $20.1(4)$ gain in the population of the $J=0$, $F=0$ hyperfine sublevel of the TlF ground state.