Generation of atomic and field squeezing by adiabatic passage and symmetry breaking

We propose an efficient scheme for realizing squeezing for both an atomic ensemble and a cavity field via adiabatic evolution of the dark state of the atom-cavity system. Controlled symmetry breaking of the Hamiltonian ensures a unique dark state for the total system, in which the atomic system or cavity mode is squeezed depending upon the choice of the detunings. Since the generation of the atomic squeezed state requires neither the cavity mode nor the atomic system to be excited, the decoherence effects are effectively suppressed. The scheme is insensitive to the uncertainty in the atomic number and imperfect timing, and the time needed for the generation of the desired squeezed state decreases as the size of the system grows. The required experimental techniques are within the scope of what can be obtained in the present cavity QED setups.