On Multiparticle Entanglement via Resonant Interaction between Light and atomic Ensembles

Multiparticle entangled states generated via interaction between narrow-band light and an ensemble of identical two-level atoms are considered. Depending on the initial photon statistics, correlation between atoms and photons can give rise to entangled states of these systems. It is found that the state of any pair of atoms interacting with weak single-mode squeezed light is inseparable and robust against decay. Optical schemes for preparing entangled states of atomic ensembles by projective measurement are described.Comment: 11 pages, 1 figure, revtex

Coherent responses of resonance atom layer to short optical pulse excitation

Coherent responses of resonance atom layer to short optical pulse excitation are numerically considered. The inhomogeneous broadening of one-photon transition, the local field effect, and the substrate dispersion are involved into analysis. For a certain intensity of incident pulses a strong coherent interaction in the form of sharp spikes of superradiation is observed in transmitted radiation. The Lorentz field correction and the substrate dispersion weaken the effect, providing additional spectral shifts. Specific features of photon echo in the form of multiple responses to a double or triple pulse excitation is discussed.Comment: only PDF,15 page

Instability and entanglement of the ground state of the Dicke model

Using tools of quantum information theory we show that the ground state of the Dicke model exhibits an infinite sequence of instabilities (quantum-phase-like transitions). These transitions are characterized by abrupt changes of the bi-partite entanglement between atoms at critical values $\kappa_j$ of the atom-field coupling parameter $\kappa$ and are accompanied by discontinuities of the first derivative of the energy of the ground state. We show that in a weak-coupling limit ($\kappa_1\leq \kappa \leq \kappa_2$) the Coffman-Kundu-Wootters (CKW) inequalities are saturated which proves that for these values of the coupling no intrinsic multipartite entanglement (neither among the atoms nor between the atoms and the field) is generated by the atom-field interaction. We analyze also the atom-field entanglement and we show that in the strong-coupling limit the field is entangled with the atoms so that the von Neumann entropy of the atomic sample (that serves as a measure of the atom-field entanglement) takes the value $S_A={1/2}\ln (N+1)$. The entangling interaction with atoms leads to a highly sub-Poissonian photon statistics of the field mode.Comment: 4 pages, 3 figure

Decay and storage of multiparticle entangled states of atoms in collective thermostat

We derive a master equation describing the collective decay of two-level atoms inside a single mode cavity in the dispersive limit. By considering atomic decay in the collective thermostat, we found a decoherence-free subspace of the multiparticle entangled states of the W-like class. We present a scheme for writing and storing these states in collective thermostat

Single-qubit operations in the double-donor structure driven by optical and voltage pulses

We study theoretically the quantum dynamics of an electron in the singlyionized double-donor structure in the semiconductor host under the influence of laser pulses whose frequencies are close to structure resonant frequencies. This system can be used as a charge qubit where the logical states are defined by the lowest two energy states of the remaining valence electron localized around one or another donor. The quantum operations are performed via resonant or Raman-like transitions between the localized (qubit) states and the excited states delocalized over the structure, combined with phase shifts between qubit states generated by voltage pulses. The possibility of realization of arbitrary single-qubit rotations is demonstrated.Comment: to appear in Phys. Rev.

Completely integrable models of non-linear optics

The models of the non-linear optics in which solitons were appeared are considered. These models are of paramount importance in studies of non-linear wave phenomena. The classical examples of phenomena of this kind are the self-focusing, self-induced transparency, and parametric interaction of three waves. At the present time there are a number of the theories based on completely integrable systems of equations, which are both generations of the original known models and new ones. The modified Korteweg-de Vries equation, the non- linear Schrodinger equation, the derivative non-linear Schrodinger equation, Sine-Gordon equation, the reduced Maxwell-Bloch equation, Hirota equation, the principal chiral field equations, and the equations of massive Thirring model are gradually putting together a list of soliton equations, which are usually to be found in non-linear optics theory.Comment: Latex, 17 pages, no figures, submitted to Pramana

Nonlinear resonance reflection from and transmission through a dense glassy system built up of oriented linear Frenkel chains: two-level models

A theoretical study of the resonance optical response of assemblies of oriented short (as compared to an optical wavelength) linear Frenkel chains is carried out using a two-level model. We show that both transmittivity and reflectivity of the film may behave in a bistable fashion and analyze how the effects found depend on the film thickness and on the inhomogeneous width of the exciton optical transition.Comment: 26 pages, 9 figure

Superradiance from an ultrathin film of three-level V-type atoms: Interplay between splitting, quantum coherence and local-field effects

We carry out a theoretical study of the collective spontaneous emission (superradiance) from an ultrathin film comprised of three-level atoms with $V$-configuration of the operating transitions. As the thickness of the system is small compared to the emission wavelength inside the film, the local-field correction to the averaged Maxwell field is relevant. We show that the interplay between the low-frequency quantum coherence within the subspace of the upper doublet states and the local-field correction may drastically affect the branching ratio of the operating transitions. This effect may be used for controlling the emission process by varying the doublet splitting and the amount of low-frequency coherence.Comment: 15 pages, 5 figure