Rotary echo tests of coherence in Rydberg-atom excitation

Rotary echoes are employed to study excitation dynamics in many-body Rydberg systems. In this method, a phase reversal of a narrow-band excitation field is applied at a variable time during the excitation pulse. The visibility of the resulting echo signal reveals the degree of coherence of the excitation process. Rotary echoes are measured for several nD(5/2) Rydberg levels of rubidium with principal quantum numbers near n = 43, where the strength of electrostatic Rydberg-atom interactions is modulated by a Forster resonance. The Rydberg-atom interactions are shown to diminish the echo visibility, in agreement with recent theoretical work. The equivalence of echo signals with spectroscopic data is demonstrated.