Tunable absorption spectrum splitting in a pulse-driven three-level system

When a strong resonant field drives a two-level system, the spectrum splits into three peaks–one centered at the frequency of the field, and two symmetric satellite peaks–known as the Mollow Triplet. Replacing this strong driving field with pulse sequences introduces tunability in the spectral properties and suppressed inhomogeneous broadening in the spectrum. It is therefore natural to explore the effects that these pulse sequences have on a three level system. Here, we study the absorption spectrum of a three-level system in the ladder configuration, where the lower transition is driven by a periodic pulse and the upper transition is probed by a weak field. The resulting absorption spectrum shows similarities with the Autler-Townes doublet with the separation between peaks instead defined by the interpulse delay rather than the Rabi frequency of the field. The spectrum also shows little dependence on the pulse carrier frequency, thus demonstrating the ability to tune the spectral response of the three-level system using experimentally-accessible pulse protocols.