Effects of pulse shape on strongly driven two-level systems

We present an experimental study of the dynamics of a two-level system driven by strong nonresonant electromagnetic pulses as a function of pulse intensity and detuning. We have explored the qualitative and quantitative behavior of the transition probability as a function of pulse area for five different temporal profiles: Lorentzian, Lorentzian squared, hyperbolic secant, hyperbolic secant squared, and Gaussian. The two-level system consists of a fine-structure doublet in sodium Rydberg states coupled by Raman transitions driven through far-off-resonance intermediate states. The pulses are in the microwave regime and have high fidelity and uniform intensity. Experiments show that, despite the similarity in the pulse shapes, the behavior of the population transfer versus intensity depends dramatically on the temporal shape and that the spectral properties and area of the pulse do not adequately describe the response.