Trapping states in the micromaser

Trapping states in the one-atom maser or micromaser are predicted by maser theory and are a direct consequence of the quantization of the electromagne tic field. They have been found in our experiment when the inversion of ato ms leaving the cavity is observed while the interaction time is scanned. Th ey correspond to quantum states of the atom-cavity system and under certain conditions represent Fock states. The trapping states occur when the atom- field dynamics complete a full evolution (or multiples thereof). Owing to f eedback through the maser dynamics, a stabilization of the photon number in the steady state field of the maser cavity is achieved.