Direct frequency-comb-driven Raman transitions in the terahertz range

TL;DR

This paper demonstrates the use of a femtosecond frequency comb to coherently drive and spectroscopically resolve terahertz-range Raman transitions in a single trapped ion, achieving high accuracy and coherence.

Contribution

It introduces a novel method for driving terahertz-range Raman transitions using a femtosecond frequency comb with high precision and coherence, applicable to various atomic and molecular systems.

Findings

Achieved spectroscopic resolution of 1.82 THz transition in trapped calcium ion.

Demonstrated Rabi oscillations with 99.3% contrast and millisecond coherence.

Improved measurement accuracy by nearly a factor of five over previous methods.

Abstract

We demonstrate the use of a femtosecond frequency comb to coherently drive stimulated Raman transitions between terahertz-spaced atomic energy levels. More specifically, we address the $3d~^2D_{3/2}$ and $3d~^2D_{5/2}$ fine structure levels of a single trapped $^{40}$Ca$^+$ ion and spectroscopically resolve the transition frequency to be $\nu_D = 1{,}819{,}599{,}021{,}534 \pm 8$ Hz. The achieved accuracy is nearly a factor of five better than the previous best Raman spectroscopy, and is currently limited by the stability of our atomic clock reference. Furthermore, the population dynamics of frequency-comb-driven Raman transitions can be fully predicted from the spectral properties of the frequency comb, and Rabi oscillations with a contrast of 99.3(6)\% and millisecond coherence time has been achieved. Importantly, the technique can be easily generalized to transitions in the sub-kHz to tens of THz range and should be applicable for driving, e.g., spin-resolved rovibrational transitions in molecules and hyperfine transitions in highly charged ions.