Interaction of bimodal fields with few-level atoms in cavities and traps

The spectacular experimental results of the last few years in cavity quantum electrodynamics and trapped ions research has led to very high level laboratory performances. Such a stimulating situation essentially stems from two decisive advancements. The first is the invention of reliable protocols for the manipulation of single atoms. The second is the ability to produce desired bosonic environments on demand. These progresses have led to the possibility of controlling the form of the coupling between individual atoms and an arbitrary number of bosonic modes. As a consequence, fundamental matter-radiation interaction models like, for instance, the JC model and most of its numerous nonlinear multiphoton generalizations, have been realized or simulated in laboratory and their dynamical features have been tested more or less in detail. This topical paper reviews the state of the art of the theoretical investigations and of the experimental observations concerning the dynamical features of the coupling between single few-level atoms and two bosonic modes. In the course of the paper we show that such a configuration provides an excellent platform for investigating various quantum intermode correlation effects tested or testable in the cavity quantum electrodynamics and trapped ion experimental realms. In particular we discuss a mode-mode correlation effect appearing in the dynamics of a two-level atom quadratically coupled to two bosonic modes. This effect, named parity effect, consists in a high sensitivity to the evenness or oddness of the total number of bosonic excitations.Comment: Topical Review. To appear on J. Mod. Op

The rotating wave system-reservoir coupling: limitations and meaning in the non-Markovian regime

This paper deals with the dissipative dynamics of a quantum harmonic oscillator interacting with a bosonic reservoir. The Master Equations based on the Rotating Wave and on the Feynman-Vernon system--reservoir couplings are compared highlighting differences and analogies. We discuss quantitatively and qualitatively the conditions under which the counter rotating terms can be neglected. By comparing the analytic solution of the heating function relative to the two different coupling models we conclude that, even in the weak coupling limit, the counter rotating terms give rise to a significant contribution in the non--Markovian short time regime. The main result of this paper is that such a contribution is actually experimentally measurable and thus relevant for a correct description of the system dynamics.Comment: 14 pages, 3 figure

Determination of rotation periods in solar-like stars with irregular sampling: the Gaia case

We present a study on the determination of rotation periods (P) of solar-like stars from the photometric irregular time-sampling of the ESA Gaia mission, currently scheduled for launch in 2013, taking into account its dependence on ecliptic coordinates. We examine the case of solar-twins as well as thousands of synthetic time-series of solar-like stars rotating faster than the Sun. In the case of solar twins we assume that the Gaia unfiltered photometric passband G will mimic the variability of the total solar irradiance (TSI) as measured by the VIRGO experiment. For stars rotating faster than the Sun, light-curves are simulated using synthetic spectra for the quiet atmosphere, the spots, and the faculae combined by applying semi-empirical relationships relating the level of photospheric magnetic activity to the stellar rotation and the Gaia instrumental response. The capabilities of the Deeming, Lomb-Scargle, and Phase Dispersion Minimisation methods in recovering the correct rotation periods are tested and compared. The false alarm probability (FAP) is computed using Monte Carlo simulations and compared with analytical formulae. The Gaia scanning law makes the rate of correct detection of rotation periods strongly dependent on the ecliptic latitude (beta). We find that for P ~ 1 d, the rate of correct detection increases with ecliptic latitude from 20-30 per cent at beta ~ 0{\deg} to a peak of 70 per cent at beta=45{\deg}, then it abruptly falls below 10 per cent at beta > 45{\deg}. For P > 5 d, the rate of correct detection is quite low and for solar twins is only 5 per cent on average.Comment: 12 pages, 18 figures, accepted by MNRA

Impact of photometric variability on age and mass determination of Young Stellar Objects: A case study on Orion Nebula Cluster

In case of pre-main sequence objects, the only way to determine age and mass is by fitting theoretical isochrones on color-magnitude (alternatively luminosity-temperature) diagrams. Since young stellar objects exhibit photometric variability over wide range in magnitude and colors, the age and mass determined by fitting isochrones is expected to be inaccurate, if not erroneous. These in turn will badly affect any study carried out on age spread and process of star formation. Since we have carried out very extensive photometric observations of the Orion Nebula Cluster (ONC), we decided to use our multi-band data to explore the influence of variability in determining mass and age of cluster members. In this study, we get the amplitudes of the photometric variability in V, R, and I optical bands of a sample of 346 ONC members and use it to investigate how the variability affects the inferred masses and ages and if it alone can take account for the age spread among the ONC members reported by earlier studies. We find that members that show periodic and smooth photometric rotational modulation have their masses and ages unaffected by variability. On other hand, we found that members with periodic but very scattered photometric rotational modulation and members with irregular variability have their masses and ages significantly affected. Moreover, using Hertzsprung-Russell (HR) diagrams we find that the observed I band photometric variability can take account of only a fraction (about 50%) of the inferred age spread, whereas the V band photometric variability is large enough to mask any age spread.Comment: Accepted by MNRAS; 17 pages, 4 Tables, 15 Figure

Misbelief and misunderstandings on the non--Markovian dynamics of a damped harmonic oscillator

We use the exact solution for the damped harmonic oscillator to discuss some relevant aspects of its open dynamics often mislead or misunderstood. We compare two different approximations both referred to as Rotating Wave Approximation. Using a specific example, we clarify some issues related to non--Markovian dynamics, non--Lindblad type dynamics, and positivity of the density matrix.Comment: 6 pages, 2 figures, added info: submitted to J. Opt. B: Quantum and Semiclass. Opt., Special Issue of the 10th Central European Workshop on Quantum Optics, reference added, discussion clarifie

Stationary entanglement induced by dissipation

The dynamics of two two-level dipole-dipole interacting atoms coupled to a common electromagnetic bath and closely located inside a lossy cavity, is reported. Initially injecting only one excitation in the two atoms-cavity system, loss mechanisms asymptotically drive the matter sample toward a stationary maximally entangled state. The role played by the closeness of the two atoms with respect to such a cooperative behaviour is carefully discussed. Stationary radiation trapping effects are found and transparently interpreted.Comment: 1 figure, submitted to Phys. Rev. Let

Lindblad and non--Lindblad type dynamics of a quantum Brownian particle

The dynamics of a typical open quantum system, namely a quantum Brownian particle in a harmonic potential, is studied focussing on its non-Markovian regime. Both an analytic approach and a stochastic wave function approach are used to describe the exact time evolution of the system. The border between two very different dynamical regimes, the Lindblad and non-Lindblad regimes, is identified and the relevant physical variables governing the passage from one regime to the other are singled out. The non-Markovian short time dynamics is studied in detail by looking at the mean energy, the squeezing, the Mandel parameter and the Wigner function of the system.Comment: 13 pages, 4 figures, v2:added discussion on Wigner function, squeezing, and Mandel paramete

A site selection model to identify optimal locations for microalgae biofuel production facilities in sicily (Italy)

The lack of sustainability and negative environmental impacts of using fossil fuel resources for energy production and their consequent increase in prices during last decades have led to an increasing interest in the development of renewable biofuels. Among possible biomass fuel sources, microalgae represent one of the most promising solutions. The present work is based on the implementation of a model that facilitates identification of optimal geographic locations for large-scale open ponds for microalgae cultivation for biofuels production. The combination of a biomass production model with specific site location parameters such as irradiance, geographical constraints, land use, topography, temperatures and CO2 for biofuels plants were identified in Sicily (Italy). A simulation of CO2 saved by using the theoretical biofuel produced in place of traditional fuel was implemented. Results indicate that the territory of Sicily offers a good prospective for these technologies and the results identify ideal locations for locating biomass fuel production facilities. Moreover, the research provides a robust method that can be tailored to the specific requirements and data availability of other territories. © Research India Publications

Loss induced collective subradiant Dicke behaviour in a multiatom sample

The exact dynamics of $N$ two-level atoms coupled to a common electromagnetic bath and closely located inside a lossy cavity is reported. Stationary radiation trapping effects are found and very transparently interpreted in the context of our approach. We prove that initially injecting one excitation only in the $N$ atoms-cavity system, loss mechanisms asymptotically drive the matter sample toward a long-lived collective subradiant Dicke state. The role played by the closeness of the $N$ atoms with respect to such a cooperative behavior is brought to light and carefully discussed.Comment: 14 pages, 6 figures, submitted to EPJ

Definition of smolder experiments for Spacelab

The feasibility of conducting experiments in space on smoldering combustion was studied to conceptually design specific smoldering experiments to be conducted in the Shuttle/Spacelab System. Design information for identified experiment critical components is provided. The analytical and experimental basis for conducting research on smoldering phenomena in space was established. Physical descriptions of the various competing processes pertaining to smoldering combustion were identified. The need for space research was defined based on limitations of existing knowledge and limitations of ground-based reduced-gravity experimental facilities