Using a single circular Rydberg atom, we have prepared two modes of a superconducting cavity in a maximally entangled state. The two modes share a single photon. The entanglement is revealed by a second atom probing the correlations between the two modes after a delay. This experiment opens interesting perspectives for quantum information manipulation and fundamental tests of quantum theory.

• Received 14 March 2001

DOI:https://doi.org/10.1103/PhysRevA.64.050301