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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.


Bucker R.,Atominstitut Vienna | Grond J.,Atominstitut Vienna | Grond J.,University of Graz | Grond J.,Wolfgang Pauli Institute | And 12 more authors.
Nature Physics | Year: 2011

In recent years, substantial progress has been made in exploringand exploiting the analogy between classical light and matter waves for fundamental investigations and applications. Extending this analogy to quantum matter-wave optics is promoted by the nonlinearities intrinsic to interacting particles and is a stepping stone towards non-classical states2,3. In light optics, twin-photon beams4 are a key element for generating the non-local correlations and entanglement required for applications such as precision metrology and quantum communication5. Similar sources for massive particles have so far been limited by the multi-mode character of the processes involved or a predominant background signal6-13. Here we present highly efficient emission of twin-atom beams into a single transversal mode of a waveguide potential. The source is a one-dimensional degenerate Bose gas 14 in the first radially excited state. We directly measure a suppression of fluctuations in the atom number difference between the beams to 0.37(3) with respect to the classical expectation, equivalent to 0.11(2) after correcting for detection noise. Our results underline the potential of ultracold atomic gases as sources for quantum matter-wave optics and should enable the implementation of schemes previously unattainable with massive particles5,15-19. © 2011 Macmillan Publishers Limited. All rights reserved.


Vaneeva O.O.,Institute of Mathematics of NAS of Ukraine | O Popovych R.,Institute of Mathematics of NAS of Ukraine | O Popovych R.,Wolfgang Pauli Institute | Sophocleous C.,University of Cyprus
Physica Scripta | Year: 2014

We discuss how point transformations can be used for the study of integrability, in particular, for deriving classes of integrable variable-coefficient differential equations. The procedure of finding the equivalence groupoid of a class of differential equations is described and then specified for the case of evolution equations. A class of fifth-order variable-coefficient Korteweg-de Vries-like equations is studied within the framework suggested. © 2014 The Royal Swedish Academy of Sciences.


Popovych R.O.,Institute of Mathematics of NAS of Ukraine | Popovych R.O.,Wolfgang Pauli Institute | Bihlo A.,University of Montréal
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.


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.


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: 2015

We study the propagation of guided light along an array of three-level atoms in the vicinity of an optical nanofiber under the condition of electromagnetically induced transparency. We examine two schemes of atomic levels and field polarizations where the guided probe field is quasilinearly polarized along the major or minor principal axis, which is parallel or perpendicular, respectively, to the radial direction of the atomic position. Our numerical calculations indicate that 200 cesium atoms in a linear array with a length of 100 μm at a distance of 200 nm from the surface of a nanofiber with a radius of 250 nm can slow down the speed of guided probe light by a factor of about 3.5 × 106 (the corresponding group delay is about 1.17 μs). In the neighborhood of the Bragg resonance, a significant fraction of the guided probe light can be reflected back with a negative group delay. The reflectivity and the group delay of the reflected field do not depend on the propagation direction of the probe field. However, when the input guided light is quasilinearly polarized along the major principal axis, the transmittivity and the group delay of the transmitted field substantially depend on the propagation direction of the probe field. Under the Bragg resonance condition, an array of atoms prepared in an appropriate internal state can transmit guided light polarized along the major principal in one specific direction even in the limit of infinitely large atom numbers. The directionality of transmission of guided light through the array of atoms is a consequence of the existence of a longitudinal component of the guided light field as well as the ellipticity of both the field polarization and the atomic dipole vector. © 2015 American Physical Society.


Pocheketa O.A.,Institute of Mathematics of NAS of Ukraine | Popovych R.O.,Institute of Mathematics of NAS of Ukraine | Popovych R.O.,Wolfgang Pauli Institute
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2012

Reduction operators of generalized Burgers equations are studied. A connection between these equations and potential fast diffusion equations with power nonlinearity of degree -1 via reduction operators is established. Exact solutions of generalized Burgers equations are constructed using this connection and known solutions of the constant-coefficient potential fast diffusion equation. © 2012 Elsevier B.V.


Grant
Agency: European Commission | Branch: FP7 | Program: MC-IIF | Phase: FP7-PEOPLE-2012-IIF | Award Amount: 248.38K | Year: 2014

Recently, it has been shown theoretically that strongly non-paraxial Bessel beams can exert an optical force on a particle that drags the latter towards the light source. However, an experimental verification of the existence of an optical drag force (ODF) with Bessel beams is very challenging. In the first subproject, we therefore propose to theoretically investigate the possibility of realizing an ODF acting on particles in the evanescent field of highly non-paraxial modes sustained by high-index optical nanofibers. Nanofiber modes are promising candidates for such investigations because they can exhibit wormhole regions with negative Poynting vector in their evanescent field. Moreover, a possible ODF could be straightforwardly demonstrated because the mode might provide both the tractor force and a gradient force that automatically traps the particles in the region with a backward force. Beyond the fundamental interest of demonstrating an ODF, its implementation with nanofiber modes may find important applications in both science and technology. In the second subproject, we propose to theoretically investigate cavity quantum electrodynamical (CQED) effects for an ensemble of fiber-trapped atoms coupled to a nanofiber-based cavity (NFC). Due to the strong lateral confinement of the NFC mode, the CQED effects prevail even if the NFC finesse is moderate (100) and the resonator is comparatively long (10 cm). Such NFCs have recently been demonstrated experimentally. Moreover, cold neutral atoms have recently been trapped and optically interfaced in the evanescent field surrounding optical nanofibers. It is therefore very timely highly appealing to consider the combination of NFCs with such nanofiber-trapped atoms. We will therefore establish the theoretical framework for the novel system and explore its potential for controlling the flow of light and for light-light interaction at the single quantum level.


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.

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