Laser-coolable AcOH$^+$ ion for $\mathcal{CP}$-violation searches

TL;DR

This study identifies AcOH$^+$ as a laser-coolable molecular ion suitable for $ ext{CP}$-violation experiments, providing detailed electronic structure calculations and feasibility analysis for experimental implementation.

Contribution

The paper presents the first detailed theoretical analysis of AcOH$^+$'s electronic structure, laser cooling potential, and its suitability for $ ext{CP}$-violation searches, linking measurable effects to fundamental physics constants.

Findings

AcOH$^+$ is linear in ground and excited states.

Laser cooling of AcOH$^+$ is feasible with a Doppler limit of ~4 nK.

The excited vibrational state's lifetime is estimated at ~0.4 seconds.

Abstract

The AcOH${}^+$ molecular ion is identified as a prospective system to search for $\mathcal{CP}$-violation effects. According to our study AcOH${}^+$ belongs to the class of laser-coolable polyatomic molecular cations implying the large coherence time in the experiments to study symmetry violating effects of fundamental interactions. We perform both nuclear and high level relativistic coupled cluster electronic structure calculations to express experimentally measurable $\mathcal{T}$,$\mathcal{P}$-violating energy shift in terms of fundamental quantities such as the nuclear magnetic quadrupole moment (MQM), electron electric dipole moment ($e$EDM) and dimensionless scalar-pseudoscalar nuclear-electron interaction constant. We further express nuclear MQM in terms of the strength constants of $\mathcal{CP}$-violating nuclear forces: quantum chromodynamics vacuum angle $\bar{\theta}$ and quark chromo-EDMs. The equilibrium geometry of AcOH${}^+$ in the ground and the four lowest excited electronic states was found to be linear. The calculated Franck-Condon factors and transition dipole moments indicate that the laser cooling using optical cycle involving the first excited state is possible for the trapped AcOH${}^+$ ions with the Doppler limit estimated to be~$\sim 4$~nK. The lifetime of the (0,1$^1$,0) excited vibrational state considered as a working one for MQM and $e$EDM search experiments is estimated to be $\sim 0.4$ sec.