Abstract

While for the most part quantum statistical processes in quantum optics are investigated in a weak-coupling regime, it has recently become possible to realize experimentally systems for which the internal coupling coefficient g is comparable to the external dissipative rates. Within this context the subject of our investigation is the quantum dynamical processes for a small collection of N two-state atoms strongly coupled to a single mode of a high finesse optical cavity.^[1,2] For our system, the coupling rate g is larger than both the cavity decay rate κ and the rate of relaxation γ⊥ of the atomic polarization, so that the number of intracavity photons required to saturate an intracavity atom is only 0.8 photons, while a single intracavity atom is sufficient to reduce the peak transmission of the cavity by a factor of 30. Because of the strong coupling, we are able to observe a normal-mode splitting for the atomcavity system even for N = 1 intracavity atom.^[1] Our measurements are made by monitoring the transmission of a weak probe beam and represent a direct spectroscopic observation of the so-called vacuum-Rabi splitting. To address nonclassical aspects of the dynamics of this open quantum system, we investigate the intensity fluctuations of the transmitted field for weak excitation and observe photon antibunching and sub-Poissonian photon statistics for N= 18,45, and 110 atoms.^[2]

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