Carrier Revival in Long Trapped-Ion Chains

TL;DR

This paper predicts that increasing the number of ions in a linear chain can revive the optical carrier excitation strength, counteracting suppression effects in long trapped-ion chains outside the Lamb-Dicke regime.

Contribution

It introduces a quantum-mechanical model showing how long ion chains can concentrate spectral strength into the carrier, enabling efficient excitation.

Findings

Long ion chains can restore strong carrier excitation.

Spectral concentration into the carrier occurs in sufficiently long chains.

Potential applications include improved multi-ion optical clocks.

Abstract

For a single trapped ion, the excitation spectrum of a narrow optical transition consists of a Doppler- and recoil-free carrier accompanied by motional sidebands, which are equally spaced by the trap secular frequency and lie under a Doppler-broadened envelope that is shifted by the photon recoil. Outside the Lamb-Dicke regime, the large photon recoil distributes the line strength across many sidebands and suppresses excitation of the carrier. With multiple ions, the motional spectrum becomes dense, and the carrier is further weakened. Here, we predict a counterintuitive revival effect: increasing the number of ions in a linear chain can restore strong carrier excitation even under trapping conditions far from the single-ion Lamb-Dicke regime. Using a quantum-mechanical model of the excitation dynamics in linear ion chains, we find that sufficiently long chains concentrate the spectrum into the carrier. This effect enables efficient excitation of light ions at short wavelengths. It may also benefit multi-ion optical clocks and mixed-species quantum-logic spectroscopy.