Abstract-Direct Frequency-Comb-Driven Raman Transitions in the Terahertz Range

C. Solaro, S. Meyer, K. Fisher, M. V. DePalatis, M. Drewsen,

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.253601

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 $40{\mathrm{Ca}}^{+}$ ion and spectroscopically resolve the transition frequency to be ${\nu }_D=1,819,599,021,534\pm 8\mathrm{Hz}$. 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 have 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.

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