Hichem Eleuch

Correlated spontaneous emission on the Danube

We consider collective spontaneous emission from an ensemble of N identical two-level atoms prepared by absorption of a single photon–a.k.a. single photon Dicke superradiance. We discuss dynamical properties of superradiance for small (R ≪ λ) and large (R ≫ λ) atomic cloud. Moreover, we address the effects of virtual processes on collective decay rate and Lamb shift. It turns out that virtual processes lead to relatively small yet interesting effects on the time evolution of a rapidly decaying state. However, such processes substantially modify the dynamics of trapped states by bringing in new channels of decay.

Light-to-matter entanglement transfer in optomechanics

We analyze a scheme to entangle the movable mirrors of two spatially separated nanoresonators via a broadband squeezed light. We show that it is possible to transfer the Einstein–Podolsky–Rosen-type continuous-variable entanglement from the squeezed light to the mechanical motion of the movable mirrors. An optimal entanglement transfer is achieved when the nanoresonators are tuned at resonance with the vibrational frequencies of the movable mirrors and when strong optomechanical coupling is attained. Stationary entanglement of the states of the movable mirrors as strong as that of the input squeezed light can be obtained for sufficiently large optomechanical cooperativity, achievable in currently available optomechanical systems. The scheme can be used to implement long-distance quantum-state transfer provided that the squeezed light interacts with the nanoresonators.

Asymptotic dynamics of quantum discord in open quantum systems

It is well known that quantum entanglement makes certain tasks in quantum information theory possible. However, there are also quantum tasks that display a quantum advantage without entanglement. Distinguishing classical and quantum correlations in quantum systems is therefore of both practical and fundamental importance. Realistic quantum systems are not closed, and therefore it is important to study the various correlations when the system loses its coherence due to interactions with the environment. In this paper, we study in detail the dynamics of different kinds of correlations, classical correlation, quantum discord and entanglement in open quantum systems, in particular, a two-qubit system evolving under Kossakowski-type quantum dynamical semigroups of completely positive maps. In such an environment, classical and quantum correlations can even persist asymptotically. By analytic and numerical analysis, we find that the quantum discord is larger than the classical correlation for asymptotic states. Furthermore, we show that the quantum discord is more resistant to the action of the environment than quantum entanglement, and it can persist even in the asymptotic long-time regime.

New analytic solution of Schrödinger's equation

We obtain an analytic solution beyond adiabatic approximation by transferring the 1D Schrodinger equation into the Ricatti equation. Then we show that our solution is more accurate than JWKB approximation. The generalizations of the approach to 3D are suggested, and possible applications of obtained solutions are discussed.

Concurrence in the framework of coherent states

The concurrence of a two-qubit nonorthogonal pure state is determined through the construction of this state in the language of spin coherent states. The generalization of this method to the case of a class of mixed states is given. The concurrence in this case is nothing but a function of the amplitude of the spin coherent states, it is shown also that probability present an interesting behavior.

Strong squeezing and robust entanglement in cavity electromechanics

(Received 29 October 2013; published 29 January 2014)We investigate nonlinear effects in an electromechanical system consisting of a superconducting charge qubitcoupled to a transmission line resonator and a nanomechanical oscillator, which in turn is coupled to anothertransmission line resonator. The nonlinearities induced by the superconducting qubit and the optomechanicalcoupling play an important role in creating optomechanical entanglement as well as the squeezing of thetransmitted microwave field. We show that strong squeezing of the microwave field and robust optomechanicalentanglementcanbeachievedinthepresenceofmoderatethermaldecoherenceofthemechanicalmode.Wealsodiscusstheeffectofthecouplingofthesuperconducting qubittothenanomechanical oscillator onthebistabilitybehavior of the mean photon number.DOI: 10.1103/PhysRevA.89.013841 PACS number(s): 42

Using quantum coherence to generate gain in the XUV and X-ray: gain-swept superradiance and lasing without inversion

It was shown some time ago that when the excitation of an ensemble of two-level atoms is swept in the direction of lasing, so that atoms are prepared in the excited state just as the radiation from previously excited atoms reaches them, the resulting laser amplifier is “highly anomalous” and yields superradiant emission without population inversion. We here show that transient gain in a three-level system has common features with Dicke superradiance and can yield strong extreme ultraviolet lasing in, for example, He atoms (at 58 nm) or He-like ions such as B3+ (at 6.1 nm).

Interaction of a quantum well with squeezed light: Quantum-statistical properties

We investigate the quantum statistical properties of the light emitted by a quantum well interacting with squeezed light from a degenerate subthreshold optical parametric oscillator. We obtain analytical solutions for the pertinent quantum Langevin equations in the strong-coupling and low-excitation regimes. Using these solutions we calculate the intensity spectrum, autocorrelation function, and quadrature squeezing for the fluorescent light. We show that the fluorescent light exhibits bunching and quadrature squeezing. We also show that the squeezed light leads to narrowing of the width of the spectrum of the fluorescent light.

Coherent control of atomic excitation using off-resonant strong few-cycle pulses

Article on coherent control of atomic excitation using off-resonant strong few-cycle pulses.

Beam splitting and entanglement generation: excited coherent states

We study the mathematical properties of the excited coherent states, which are obtained through actions of a photon creation operator of the mode optical field on its corresponding coherent state, by analyzing the minimal set of Klauder’s coherent states. Using linear entropy as a measure of entanglement, we investigate in detail the entanglement generated via a beam splitter when an excited coherent state is injected on one input mode and vacuum state is injected on the other one. Finally, we examine the physical properties of the excited coherent states through the Mandel’s parameter and the Wehrl entropy and we give the correlation between these parameters and the entanglement of the output state.