Rydberg ions in coherent motional states: A new method for determining the polarizability of Rydberg ions

TL;DR

This paper introduces a novel method to measure the polarizability of Rydberg ions using their motional states in a Paul trap, enabling more precise quantum gate operations.

Contribution

The method allows for direct measurement of Rydberg ion polarizability through motional state analysis, applicable across various Rydberg states and quantum numbers.

Findings

Polarizability measurements agree with numerical calculations.

The method is easy to implement and versatile.

Accurate polarizability values aid quantum gate development.

Abstract

We present a method for measuring the polarizability of Rydberg ions confined in the harmonic potential of a Paul trap. For a highly excited electronic state, the coupling between the electronic wave function and the trapping field modifies the excitation probability depending on the motional state of the ion. This interaction strongly depends on the polarizability of the excited state and manifests itself in the state-dependent secular frequencies of the ion. We initialize a single trapped $^{40}$Ca$^+$ ion from the motional ground state into coherent states with $|\alpha|$ up to 12 using electric voltages on the trap segments. The internal state, firstly initialised in the long-lived 3D$_{5/2}$ state, is excited to a Rydberg S$_{1/2}$-state via the 5P$_{3/2}$ state in a two-photon process. We probe the depletion of the 3D$_{5/2}$ state owing to the Rydberg excitation followed by a decay into the internal ground 4S$_{1/2}$ state. By analysing the obtained spectra we extract the polarizability of Rydberg states which agree with numerical calculations. The method is easy-to-implement and applicable to different Rydberg states regardless of their principal or angular quantum numbers. An accurate value of the state polarizability is needed for quantum gate operations with Rydberg ion crystals.