Quantum correlations of an atomic ensemble via an incoherent bath (5 pages)

Y.-x. Liu, YueYang Li, C. P. Sun +1 more

Mihai Macovei, Jörg Evers, Christoph H. Keitel

A rich variety of quantum features can be found in a collection of atoms driven only by an incoherent bath. To demonstrate this, we discuss a sample of three-level atoms in ladder configuration interacting via the surrounding bath, and show that the fluorescence light emitted by this system exhibits nonclassical properties. Realizations could be thermal baths for microwave transitions, or incoherent broadband fields for optical transitions. In a small sample of atoms, the emitted light can be switched from sub- to super-Poissonian and from antibunching to superbunching controlled by the mean number of atoms in the sample. Larger samples allow us to generate superbunched light over a wide range of bath parameters and thus fluorescence light intensities. We also identify parameter ranges where the fields emitted on the two transitions are strongly correlated or anticorrelated, such that the Cauchy-Schwarz inequality is violated. As in a moderately strong bath this violation occurs also for larger numbers of atoms, such samples exhibit macroscopic quantum effects.

Richard Healey

Guido Bellomo, A. P. Majtey, Angel Ricardo Plastino +1 more

Nick J. Schilder, Christophe Sauvan, Yvan R. P. Sortais +2 more

We study theoretically the concept of homogenization in optics using an ensemble of randomly distributed resonant stationary atoms with density $\ensuremath{\rho}$. The ensemble is dense enough for the usual condition for homogenization, viz. $\ensuremath{\rho}{\ensuremath{\lambda}}^{3}\ensuremath{\gg}1$, to be reached. Introducing the coherent and incoherent scattered powers, we define two criteria to define the homogenization regime. We find that when the excitation field is tuned in a broad frequency range around the resonance, neither of the criteria for homogenization is fulfilled, meaning that the condition $\ensuremath{\rho}{\ensuremath{\lambda}}^{3}\ensuremath{\gg}1$ is not sufficient to characterize the homogenized regime around the atomic resonance. We interpret these results as a consequence of the light-induced dipole-dipole interactions between the atoms, which implies a description of scattering in terms of collective modes rather than as a sequence of individual scattering events. Finally, we show that, although homogenization can never be reached for a dense ensemble of randomly positioned laser-cooled atoms around resonance, it becomes possible if one introduces spatial correlations in the positions of the atoms or nonradiative losses, such as would be the case for organic molecules or quantum dots coupled to a phonon bath.

K. Eckert, John Schliemann, Dagmar Bruß +1 more