  We report the observation of coherent oscillations in conversion efficiency
of weakly-bound dimers formed from a thermal gas of ultracold atoms. Finite
thermal energy of the gas causes loss of coherence when a broad continuum is
resonantly coupled to a discrete bound state. Restoration of the coherence can
be achieved through non-adiabatic transitions of the dressed molecular energy
level that are induced by a strong modulation pulse with fast envelope
dynamics. Conditions to observe coherent oscillations are verified, and control
of their properties is demonstrated. The main experimental findings are
supported by theoretical modeling and numerical calculations. The observed
results may lead to a renewed interest in general studies of a discrete energy
level coupled to a broadband continuum when the properties of both are fully
controlled.

Quantum Gases;Atomic Physics;Quantum Physics