Coherent control of interaction and entanglement of a Rydberg atom with few photons

The interaction of a model Rydberg atom with a single photon quantum field is investigated. The atom is considered in the model of 'several bound states + continuum', so that the field-induced ionization from initially populated Rydberg states as well as the resonance coupling with a lower-lying bound state are taken into account. The significant suppression of the ionization due to interference mechanism is established and strong entanglement with a quantum field subsystem is found. Methods to control the atomic behavior and to produce strongly entangled atom-photon states are suggested. The possibility to measure the degree of entanglement experimentally is demonstrated.