New insights into quantum Rabi oscillations in a coherent field

Direct investigation of the coherent field evolution is reported. A system of homodyne detection to measure the evolution of the phase, is developed and non trivial effects of the interaction upon the field is found. Initial coherent field is shown to split into two macroscopically different phase components, correlated to the initial value of the dipole operator of the atom. Experimental apparatus uses circular Rydberg atoms interacting with the mode of a high-finesse microwave cavity containing a small coherent field.