Single-atom and two-atom Ramsey interferometry with quantized fields

Implications of field quantization on Ramsey interferometry are discussed and general conditions for the occurrence of interference are obtained. Interferences do not occur if the fields in two Ramsey zones have a precise number of photons. However, in this case we show how an analog of Hanbury-Brown Twiss photon-photon correlation interferometry can be used to discern a variety of interference effects as the two independent Ramsey zones get entangled by the passage of the first atom. Interferences are restored by working with fields at a single-photon level. Generation of entangled states including states such as |2,0〉+e^iθ|0,2〉 is discussed.