Quantum Coherence and Correlations of optical radiation by atomic ensembles interacting with a two-level atom in microwave cavity

We examine quantum statistics of optical photons emitted from atomic ensembles which are classically driven and simultaneously coupled to a two-level atom via microwave photon exchange. Quantum statistics and correlations are analyzed by calculating second order coherence degree, von Neumann entropy, spin squeezing for multi-particle entanglement, as well as genuine two and three-mode entanglement parameters for steady state and non-equilibrium situations. Coherent transfer of population between the radiation modes and quantum state mapping between the two-level atom and the optical modes are discussed. A potential experimental realization of the theoretical results in a superconducting coplanar waveguide resonator containing diamond crystals with Nitrogen-Vacancy color centers and a superconducting artificial two-level atom is discussed.Comment: 15 pages, 17 figures, submitted to Phys. Rev.

Emergent Radiation in an Atom-Field System at Twice-Resonance

A two-level atom interacting with a single mode of quantized electromagnetic radiation is discussed using a representation in which the atom and the radiation are unified into a {\em new} canonical radiation. At the {\em twice-resonance}, when the frequency of the original radiation is twice the atomic transition frequency ($\omega=2\epsilon$), the {\em emergent} unified field in the non-interacting atom-field system resembles a free radiation of frequency $\epsilon$. This free emergent radiation is further shown to exist in the presence of an interaction which looks similar to the atom-field interaction in the dipole approximation. The one-photon correlation and the population inversion are discussed as the possible means of observing the emergent radiation. The entanglement properties of the emergent radiation are also discussed.Comment: 4+ pages, 2 figures, submitted for publication; included a discussion on the entanglemen

Multimode quantum limits to the linewidth of an atom laser

The linewidth of an atom laser can be limited by excitation of higher energy modes in the source Bose-Einstein condensate, energy shifts in that condensate due to the atomic interactions, or phase diffusion of the lasing mode due to those interactions. The first two are effects that can be described with a semiclassical model, and have been studied in detail for both pumped and unpumped atom lasers. The third is a purely quantum statistical effect, and has been studied only in zero dimensional models. We examine an unpumped atom laser in one dimension using a quantum field theory using stochastic methods based on the truncated Wigner approach. This allows spatial and statistical effects to be examined simultaneously, and the linewidth limit for unpumped atom lasers is quantified in various limits.Comment: 8 Figure

Shot noise spectrum of superradiant entangled excitons

The shot noise produced by tunneling of electrons and holes into a double dot system incorporated inside a p-i-n junction is investigated theoretically. The enhancement of the shot noise is shown to originate from the entangled electron-hole pair created by superradiance. The analogy to the superconducting cooper pair box is pointed out. A series of Zeno-like measurements is shown to destroy the entanglement, except for the case of maximum entanglement.Comment: 5 pages, 3 figures, to appear in Phys. Rev. B (2004

Quantum optical effective-medium theory for loss-compensated metamaterials

A central aim in metamaterial research is to engineer sub-wavelength unit cells that give rise to desired effective-medium properties and parameters, such as a negative refractive index. Ideally one can disregard the details of the unit cell and employ the effective description instead. A popular strategy to compensate for the inevitable losses in metallic components of metamaterials is to add optical gain material. Here we study the quantum optics of such loss-compensated metamaterials at frequencies for which effective parameters can be unambiguously determined. We demonstrate that the usual effective parameters are insufficient to describe the propagation of quantum states of light. Furthermore, we propose a quantum-optical effective-medium theory instead and show that it correctly predicts the properties of the light emerging from loss-compensated metamaterials.Comment: 6 pages, 3 figures. Accepted for Physical Review Letter

Spatial Correlation Functions of one-dimensional Bose gases at Equilibrium

The dependence of the three lowest order spatial correlation functions of a harmonically confined Bose gas on temperature and interaction strength is presented at equilibrium. Our analysis is based on a stochastic Langevin equation for the order parameter of a weakly-interacting gas. Comparison of the predicted first order correlation functions to those of appropriate mean field theories demonstrates the potentially crucial role of density fluctuations on the equilibrium coherence length. Furthermore,the change in both coherence length and shape of the correlation function, from gaussian to exponential, with increasing temperature is quantified. Moreover, the presented results for higher order correlation functions are shown to be in agreeement with existing predictions. Appropriate consideration of density-density correlations is shown to facilitate a precise determination of quasi-condensate density profiles, providing an alternative approach to the bimodal density fits typically used experimentally

Phase modulation induced by cooperative effects in electromagnetically induced transparency

We analyze the influence of dipole-dipole interactions in an electromagnetically induced transparency setup at high density. We show both analytically and numerically that the polarization contribution to the local field strongly modulates the phase of a weak pulse. We give an intuitive explanation for this local field induced phase modulation and show that it distinctively differs from the nonlinear self-phase modulation a strong pulse experiences in a Kerr medium

Optically-Induced Polarons in Bose-Einstein Condensates: Monitoring Composite Quasiparticle Decay

Nonresonant light-scattering off atomic Bose-Einstein condensates (BECs) is predicted to give rise to hitherto unexplored composite quasiparticles: unstable polarons, i.e., local ``impurities'' dressed by virtual phonons. Optical monitoring of their spontaneous decay can display either Zeno or anti-Zeno deviations from the Golden Rule, and thereby probe the temporal correlations of elementary excitations in BECs.Comment: 4 pages, 3 figure