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Breitenfurt bei Wien, Austria

Perrin A.,Atominstitut Vienna | Perrin A.,Wolfgang Pauli Institute | Perrin A.,University of Paris 13 | Bucker R.,Atominstitut Vienna | And 7 more authors.
Nature Physics | Year: 2012

Hanbury Brown and Twiss correlations - correlations in far-field intensity fluctuations - yield fundamental information on the quantum statistics of light sources, as demonstrated after the discovery of photon bunching 1-3. Drawing on the analogy between photons and atoms, similar measurements have been performed for matter-wave sources, probing density fluctuations of expanding ultracold Bose gases 4-8. Here we use two-point density correlations to study how coherence is gradually established when crossing the Bose-Einstein condensation threshold. Our experiments reveal a persistent multimode character of the emerging matter-wave as seen in the non-trivial spatial shape of the correlation functions for all probed source geometries, from nearly isotropic to quasi-one-dimensional, and for all probed temperatures. The qualitative features of our observations are captured by ideal Bose gas theory 9, whereas the quantitative differences illustrate the role of particle interactions. © 2012 Macmillan Publishers Limited. All rights reserved.

Scrinzi A.,Ludwig Maximilians University of Munich | Scrinzi A.,Wolfgang Pauli Institute
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2010

We introduce infinite range exterior complex scaling (irECS) which provides for complete absorption of outgoing flux in numerical solutions of the time-dependent Schrödinger equation with strong infrared fields. This is demonstrated by computing high harmonic spectra and wave-function overlaps with the exact solution for a one-dimensional model system and by three-dimensional calculations for the H atom and an Ne atom model. We lay out the key ingredients for correct implementation and identify criteria for efficient discretization. © 2010 The American Physical Society.

Le Kien F.,Wolfgang Pauli Institute | Rauschenbeutel A.,Vienna University of Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2016

We investigate spontaneous emission of a two-level atom with an arbitrarily polarized electric dipole in front of a flat dielectric surface. We treat the general case where the atomic dipole matrix element is a complex vector, that is, the atomic dipole can rotate with time in space. We calculate the rates of spontaneous emission into evanescent and radiation modes. We systematically study the angular densities of the rates in the space of wave vectors for the field modes. We show that the asymmetry of the angular density of the spontaneous emission rate under central inversion in the space of in-plane wave vectors occurs when the ellipticity vector of the atomic dipole polarization overlaps with the ellipticity vector of the field mode polarization. © 2016 American Physical Society.

Le Kien F.,Wolfgang Pauli Institute | Rauschenbeutel A.,Vienna University of Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2016

We study all-optical switches operating on a single four-level atom with the N-type transition configuration in a two-mode nanofiber cavity with a significant length (on the order of 20 mm) and a moderate finesse (on the order of 300) under the electromagnetically induced transparency (EIT) conditions. In our model, the gate and probe fields are the quantum nanofiber-cavity fields excited by weak classical light pulses, and the parameters of the D2 line of atomic cesium are used. We examine two different switching schemes. The first scheme is based on the effect of the presence of a photon in the gate mode on the EIT of the probe mode. The second scheme is based on the use of EIT to store a photon of the gate mode in the population of an appropriate atomic level, which leads to the reduction of the transmission of the field in the probe mode. We investigate the dependencies of the switching contrast on various parameters, such as the cavity length, the mirror reflectivity, and the detunings and powers of the cavity driving field pulses. For a nanofiber cavity with fiber radius of 250 nm, cavity length of 20 mm, and cavity finesse of 313 and a cesium atom at a distance of 200 nm from the fiber surface, we numerically obtain a switching contrast on the order of about 67% for the first scheme and of about 95% for the second scheme. These switching operations require small mean numbers of photons in the nanofiber cavity gate and probe modes. © 2016 American Physical Society.

Popovych R.O.,Institute of Mathematics of NAS of Ukraine | Popovych R.O.,Wolfgang Pauli Institute | Bihlo A.,University of Montreal
Journal of Mathematical Physics | Year: 2012

Methods for the design of physical parameterization schemes that possess certain invariance properties are discussed. These methods are based on different techniques of group classification and provide means to determine expressions for unclosed terms arising in the course of averaging of nonlinear differential equations. The demand that the averaged equation is invariant with respect to a subalgebra of the maximal Lie invariance algebra of the unaveraged equation leads to a problem of inverse group classification which is solved by the description of differential invariants of the selected subalgebra. Given no prescribed symmetry group, the direct group classification problem is relevant. Within this framework, the algebraic method or direct integration of determining equations for Lie symmetries can be applied. For cumbersome parameterizations, a preliminary group classification can be carried out. The methods presented are exemplified by parameterizing the eddy vorticity flux in the averaged vorticity equation. In particular, differential invariants of (infinite-dimensional) subalgebras of the maximal Lie invariance algebra of the unaveraged vorticity equation are computed. A hierarchy of normalized subclasses of generalized vorticity equations is constructed. Invariant parameterizations possessing minimal symmetry extensions are described and a restricted class of invariant parameterization is exhaustively classified. The physical importance of the parameterizations designed is discussed. © 2012 American Institute of Physics.

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