Static Laboratory-Frame Polarization of a Trapped Molecular Ion for CP-Violation Searches

TL;DR

This paper demonstrates that heavy molecular ions can be statically polarized in a Paul trap, enabling sensitive CP-violation searches via molecular EDM measurements with quantum-logic clocks.

Contribution

It introduces a method to polarize molecular ions with static electric fields in a trap, overcoming previous assumptions and enabling new precision measurements.

Findings

Molecular ions can be polarized in a Paul trap using static fields.

Equilibrium positions are achieved through a balance of electrostatic and ponderomotive forces.

This enables long interrogation times and quantum-logic clock operation for EDM searches.

Abstract

Today's most sensitive experiments for detecting CP-violating permanent electric dipole moments (EDM) rely on molecular spectroscopy. The high sensitivity arises from large internal electric fields that interact with the constituents of the molecule. For molecular ions it has long been assumed that experiments with static polarization from dc electric fields are infeasible, as the ion's charge would either shift it to a field free region or eject it from the trap. This constraint appears to make single ion quantum-logic clocks, among the most precise measurement devices available, incompatible with EDM measurements. Here, we demonstrate that, under typical trapping conditions, heavy molecular ions with small $\Omega/\Lambda$-doubling can be polarized by a static electric field while remaining confined in the Paul trap. This effect arises from a cancellation between the electrostatic force and the trap's ponderomotive force, resulting in an equilibrium position where the ion experiences a dc electric field component. Dynamic decoupling allows to implement co-magnetometry schemes in a single molecule and provides long interrogation times. This will allow the operation of a quantum-logic molecular radio-frequency clock in static electric fields, providing sensitivity to EDMs. Working with only a few ions and non-destructive detection techniques opens the door to the use of highly sensitive, rare, and radioactive molecular species as well as quantum-enhanced metrology schemes to achieve unprecedented levels of accuracy and precision.