Jean-Michel Raimond, 
Université Pierre et Marie Curie, Laboratoire Kastler Brossel, ENS

Place: Room G (F207), Applied Physics

Time:  16.00 hours

Abstract

Circular Rydberg atoms are very sensitive probes of millimeter-wave quantum fields stored in high quality superconducting cavities. They make it possible to count the number of photons in an ideal Quantum Non Demolition way. This photon counting procedure leads to a vivid manifestation of the Quantum Zeno effect. It is at the heart of a complete determination of the field's quantum state, applied to Fock and Schrödinger cat states. With this time-resolved method, we follow in real time the fast decoherence of these non-classical states.

We shall discuss these experiments and the perspectives they open, particularly for the exploration of the quantum/classical boundary and for active quantum feedback. Information extracted from a partial field-intensity measurement can be used to react on the cavity with a coherent source and steer its evolution towards a prescribed Fock state. This scheme leads to an on-demand preparation of Fock states and to their protection from decoherence.