Electromagnetically Induced Transparency in strongly interacting Rydberg Gases

We develop an efficient Monte-Carlo approach to describe the optical response of cold three-level atoms in the presence of EIT and strong atomic interactions. In particular, we consider a "Rydberg-EIT medium" where one involved level is subject to large shifts due to strong van der Waals interactions with surrounding Rydberg atoms. We find excellent agreement with much more involved quantum calculations and demonstrate its applicability over a wide range of densities and interaction strengths. The calculations show that the nonlinear absorption due to Rydberg-Rydberg atom interactions exhibits universal behavior

Nonlocal Nonlinear Optics in cold Rydberg Gases

We present an analytical theory for the nonlinear optical response of a strongly interacting Rydberg gas under conditions of electromagnetically induced transparency. Simple formulae for the third order optical susceptibility are derived and shown to be in excellent agreement with recent experiments. The obtained expressions reveal strong nonlinearities, which in addition are of highly nonlocal character. This property together with enormous strength of the Rydberg-induced nonlinearities is shown to yield a unique laboratory platform for nonlinear wave phenomena, such as collapse-arrested modulational instabilities in a self-defocussing medium.Comment: 5 pages, 5 figure

Two-dimensional boson-fermion mixtures

Using mean-field theory, we study the equilibrium properties of boson-fermion mixtures confined in a harmonic pancake-shaped trap at zero temperature. When the modulus of the s-wave scattering lengths are comparable to the mixture thickness, two-dimensional scattering events introduce a logarithmic dependence on density in the coupling constants, greatly modifying the density profiles themselves. We show that for the case of a negative boson-fermion three-dimensional s-wave scattering length, the dimensional crossover stabilizes the mixture against collapse and drives it towards spatial demixing.Comment: 9 pages, 4 figure

Dynamics of Phononic Dissipation at the Atomic Scale: Dependence on Internal Degrees of Freedom

Dynamics of dissipation of a local phonon distribution to the substrate is a key issue in friction between sliding surfaces as well as in boundary lubrication. We consider a model system consisting of an excited nano-particle which is weakly coupled with a substrate. Using three different methods we solve the dynamics of energy dissipation for different types of coupling between the nano-particle and the substrate, where different types of dimensionality and phonon densities of states were also considered for the substrate. In this paper, we present our analysis of transient properties of energy dissipation via phonon discharge in the microscopic level towards the substrate. Our theoretical analysis can be extended to treat realistic lubricant molecules or asperities, and also substrates with more complex densities of states. We found that the decay rate of the nano-particle phonons increases as the square of the interaction constant in the harmonic approximation.Comment: 10 pages, 6 figures, submitted to Phys. Rev.

Thermodynamic properties of harmonically trapped D-dimensional ideal gases within generalized exclusion statistics

We consider an ideal gas trapped with harmonic potential and obeying the generalized exclusion statistics. We analytically calculate the density of states from which the thermodynamic properties of the gas are calculated for a general energy spectrum ε (p) = a ps in D-dimensional space. Internal energy and the specific heat as a function of temperature are evaluated numerically for different dimensions and energy-momentum dispersion relations. In particular, we show that the specific heat is independent of the statistical parameter g for the constant density of states regime which corresponds D = 1 and s = 2 for this system. © 2007 Elsevier B.V. All rights reserved

Superlattice Structures of Graphene based Nanoribbons

Based on first-principles calculations we predict that periodically repeated junctions of armchair graphene nanoribbons of different widths form superlattice structures. In these superlattice heterostructures the width and the energy gap are modulated in real space and specific states are confined in certain segments. Orientation of constituent nanoribbons, their width and length, the symmetry of the junction are the structural parameters to engineer electronic properties of these quantum structures. Not only the size modulation, but also composition modulation, such as periodically repeated, commensurate heterojunctions of BN and graphene honeycomb nanoribbons result in a multiple quantum well structure. We showed that these graphene based quantum structures can introduce novel concepts to design nanodevices.Comment: amended versio

Ground-State properties and collective excitations in a 2D Bose-Einstein condensate with gravity-like interatomic attraction

We study the ground-state properties of a Bose-Einstein condensate (BEC) with the short-range repulsion and gravitylike 1/r interatomic attraction in two-dimensions (2D). Using the variational approach, we obtain the ground-state energy and show that the condensate is stable for all interaction strenghts in 2D. We also determine the collective excitations at zero temperature using the time-dependent variational method. We analyze the properties of the Thomas-Fermi-gravity (TF-G) and gravity (G) regimes. © Springer Science+Business Media, LLC 2007

Ground-state properties, vortices, and collective excitations in a two-dimensional Bose-Einstein condensate with gravitylike interatomic attraction

We study the ground-state properties of a Bose-Einstein condensate with short-range repulsion and gravitylike 1/r interatomic attraction in two-dimensions (2D). Using the variational approach we obtain the ground-state energy and analyze the stability of the condensate for a range of interaction strengths in 2D. We also determine the collective excitations at zero temperature using the time-dependent variational method. We analyze the properties of the Thomas-Fermi-gravity and gravity regimes, and we examine the vortex states, finding the coherence length and monopole mode frequency for these regimes. Our results are compared and contrasted with those in 3D condensates. © 2008 The American Physical Society

Functionalization of graphene nanoribbons

With the synthesis of a single atomic plane of graphite, namely, graphene honeycomb structure, a new perspective for carbon-based electronics is opened. The one-dimensional graphene nanoribbons (GNRs) have different band-gap values depending on their edge shape and width. In this contribution, we report our results showing that repeated heterostructures of GNRs of different widths form multiple quantum-well structures. The widths of the constituent parts as well as the bandgap, and also the magnetic ground state of the superlattices are modulated in direct space. We provide detailed analysis of these structures and show that superlattices with armchair edge shapes can be used as resonant tunneling devices and those with zigzag edge shape have unique features for spintronic applications. We also discuss another route of functionalizing 2D graphene, 1D GNR, and superlattices with 3d-transition metal (TM) atom adsorption. © Springer-Verlag Berlin Heidelberg 2013

Dependence of the cloud size on interactions for a trapped degenerate ultracold plasma

We consider an ultracold plasma that has bosonic ions, at zero temperature. Assuming that ions are trapped by a harmonic trap, we calculate the size of the cloud for both screened and bare Coulomb interactions. Our results indicate that if clouds containing around 104 ions are confined with a trapping frequency of 10 kHz, stable radius is 15 μm for a fully screened two-component plasma while the radius increases to 2 mm for a one component plasma. © 2005 Elsevier B.V. All rights reserved