ORBi Collection: Physics
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Fabrication and operation of a two-dimensional ion-trap lattice on a high-voltage microchip
http://hdl.handle.net/2268/178841
Title: Fabrication and operation of a two-dimensional ion-trap lattice on a high-voltage microchip
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<br/>Author, co-author: Sterling, Robin C.; Rattanasonti, Hwanjit; Weidt, Sebastian; Lake, Kim; Srinivasan, Prasanna; Webster, S. C.; Kraft, Michaël; Hensinger, Winfried K.Mon, 02 Mar 2015 17:09:16 GMTDynamics and statistics of wave-particle interactions in a confined geometry
http://hdl.handle.net/2268/178755
Title: Dynamics and statistics of wave-particle interactions in a confined geometry
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<br/>Author, co-author: Gilet, TristanThu, 26 Feb 2015 21:44:44 GMTTensor Representation of Spin States
http://hdl.handle.net/2268/178741
Title: Tensor Representation of Spin States
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<br/>Author, co-author: Giraud, Olivier; Braun, Daniel; Baguette, Dorian; Bastin, Thierry; Martin, John
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<br/>Abstract: We propose a generalization of the Bloch sphere representation for arbitrary spin states. It provides a compact and elegant representation of spin density matrices in terms of tensors that share the most important properties of Bloch vectors. Our representation, based on covariant matrices introduced by Weinberg in the context of quantum field theory, allows for a simple parametrization of coherent spin states, and a straightforward transformation of density matrices under local unitary and partial tracing operations. It enables us to provide a criterion for anticoherence, relevant in a broader context such as quantum polarization of light.Thu, 26 Feb 2015 15:59:41 GMTGranular transport in driven granular gas
http://hdl.handle.net/2268/178668
Title: Granular transport in driven granular gas
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<br/>Author, co-author: Noirhomme, Martial; Opsomer, Eric; Ludewig, François; Vandewalle, Nicolas
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<br/>Abstract: We numerically and theoretically investigate the behavior of a granular gas driven by asymmetric plates. The injection of energy in the dissipative system differs from one side to the opposite one. We prove that the dynamical clustering which is expected for such a system is affected by the asymmetry. As a consequence, the cluster position can be fully controlled. This property could lead to various applications in the handling of granular materials in low-gravity environment. Moreover, the dynamical cluster is characterized by natural oscillations which are also captured by a model. These oscillations are mainly related to the cluster size, thus providing an original way to probe the clustering behavior.Wed, 25 Feb 2015 10:32:56 GMTSize and porosity effects on thermal conductivity of nanoporous material with an extension to nanoporous particles embedded in a host matrix
http://hdl.handle.net/2268/178648
Title: Size and porosity effects on thermal conductivity of nanoporous material with an extension to nanoporous particles embedded in a host matrix
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<br/>Author, co-author: Machrafi, Hatim; Lebon, GeorgyTue, 24 Feb 2015 15:05:12 GMTEffective thermal conductivity of spherical particulate nanocomposites: comparison with theoretical models, Monte Carlo simulations and experiments
http://hdl.handle.net/2268/178647
Title: Effective thermal conductivity of spherical particulate nanocomposites: comparison with theoretical models, Monte Carlo simulations and experiments
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<br/>Author, co-author: Machrafi, Hatim; Lebon, GeorgyTue, 24 Feb 2015 15:03:54 GMTClustering and segregation in driven granular fluids
http://hdl.handle.net/2268/178642
Title: Clustering and segregation in driven granular fluids
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<br/>Author, co-author: Opsomer, Eric; Vandewalle, Nicolas; Noirhomme, Martial; Ludewig, François
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<br/>Abstract: In microgravity, the successive inelastic collisions in a granular gas can lead to a dynamical clustering of the particles. This transition depends on the filling fraction of the system, the restitution of the used materials and on the size of the particles. We report simulations of driven bi-disperse gas made of small and large spheres. The size as well as the mass difference imply a strong modification in the kinematic chain of collisions and therefore alter significantly the formation of a cluster. Moreover, the different dynamical behaviors can also lead to a demixing of the system, adding a few small particles in a gas of large ones can lead to a partial clustering of the taller type. We realized a detailed phase diagram recovering the encountered regimes and developed a theoretical model predicting the possibility of dynamical clustering in binary systems.Tue, 24 Feb 2015 14:18:22 GMTLattice dynamics and magnetic properties in selected functional iron compounds
http://hdl.handle.net/2268/178394
Title: Lattice dynamics and magnetic properties in selected functional iron compounds
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<br/>Author, co-author: Herlitschke, Marcus
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<br/>Abstract: The presented thesis reports about to the investigation of four different materials with respect to
their magnetic properties and their lattice dynamics. The carbodiimide FeNCN, which was recently synthesized for the first time and can be considered as an non-oxidic analogue to FeO, is discussed in chapter 2. The NCN 2− group bridges two iron and exhibits a double negative charge, similar to the oxygen in FeO. This material exhibits an increased magnetic order temperature as compared to FeO. FeNCN was investigated with magnetometry, Mössbauer spectroscopy and nuclear inelastic scattering, revealing an unusual behaviour of the hyperfine parameters below the ordering temperature. This observation is discussed with respect to the crystal field and the d-orbital level population with temperature.
The investigation of the magnetocaloric material Mn5−x FexSi3 is reported in chapter 3 with focus on the interaction of magnetism and lattice dynamics. Among the Mn5−xFe x Si3 compounds, MnFe4 Si3 is the most interesting one due to the possible application as a room temperature refrigeration material. The investigation reveals that a direct measurement of the influence of the magnetocaloric effect on the density of iron phonon states is not possible, however, the elasticity was observed to be strongly influenced by this effect.
The studies on the spin orientation in nanospheres and a NANOPERM alloy are discussed in chap
ter 4 and chapter 5. Two approaches were followed in order to investigated the spin orientation,
nuclear forward scattering and nuclear resonant small-angle X-ray scattering. In the first part,
maghemite nanospheres are analysed with in-field nuclear forward scattering, revealing that the
spins orient only partially along the direction of the applied magnetic field. A modeled magnetization calculated from the observed degree of spin orientation matches excellently the macroscopic magnetometry data and literature values. Though revealing the amount of oriented spins, nuclear forward scattering is not sensitive to their position in the nanoparticles. Thus, the nuclear forward scattering was combined with small-angle X-ray scattering, leading to small-angle patterns in dependence of the local spin orientation in the aforementioned samples.Mon, 16 Feb 2015 11:36:00 GMTEarly history of extended irreversible thermodynamics (1953-1983): an exploration beyond local equilibrium and classical transport theory
http://hdl.handle.net/2268/178392
Title: Early history of extended irreversible thermodynamics (1953-1983): an exploration beyond local equilibrium and classical transport theory
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<br/>Author, co-author: Lebon, Georgy; Jou, davidMon, 16 Feb 2015 11:01:50 GMTOrigin of the exponential decay of the Loschmidt echo in integrable systems
http://hdl.handle.net/2268/178322
Title: Origin of the exponential decay of the Loschmidt echo in integrable systems
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<br/>Author, co-author: Dubertrand, Rémy; Goussev, A
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<br/>Abstract: We address the time decay of the Loschmidt echo, measuring the sensitivity of quantum dynamics to small Hamiltonian perturbations, in one-dimensional integrable systems. Using a semiclassical analysis, we show that the Loschmidt echo may exhibit a well-pronounced regime of exponential decay, similar to the one typically observed in quantum systems whose dynamics is chaotic in the classical limit. We derive an explicit formula for the exponential decay rate in terms of the spectral properties of the unperturbed and perturbed Hamilton operators and the initial state. In particular, we show that the decay rate, unlike in the case of the chaotic dynamics, is directly proportional to the strength of the Hamiltonian perturbation. Finally, we compare our analytical predictions against the results of a numerical computation of the Loschmidt echo for a quantum particle moving inside a one-dimensional box with Dirichlet-Robin boundary conditions, and find the two in good agreement.Fri, 13 Feb 2015 14:44:29 GMTTrace formula for dielectric cavities. III. TE modes
http://hdl.handle.net/2268/178321
Title: Trace formula for dielectric cavities. III. TE modes
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<br/>Author, co-author: Bogomolny, E; Dubertrand, Rémy
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<br/>Abstract: The construction of the semiclassical trace formula for resonances with transverse electric polarization for two-dimensional dielectric cavities is discussed. Special attention is given to the derivation of the two first terms of Weyl’s series for the average number of such resonances. The formulas obtained agree well with numerical calculations for dielectric cavities of different shapes.Fri, 13 Feb 2015 14:41:47 GMTTrace formula for chaotic dielectric resonators tested with microwave experiments
http://hdl.handle.net/2268/178320
Title: Trace formula for chaotic dielectric resonators tested with microwave experiments
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<br/>Author, co-author: Bittner, S; Dietz, B; Dubertrand, Rémy; Isensee, J; Miski-Oglu, M; Richter, A
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<br/>Abstract: We measured the resonance spectra of two stadium-shaped dielectric microwave resonators and tested a semiclassical trace formula for chaotic dielectric resonators proposed by Bogomolny et al. [Phys. Rev. E 78, 056202 (2008)]. We found good qualitative agreement between the experimental data and the predictions of the trace formula. Deviations could be attributed to missing resonances in the measured spectra in accordance with previous experiments [Phys. Rev. E 81, 066215 (2010)]. The investigation of the numerical length pectrum
showed good qualitative and reasonable quantitative agreement with the trace formula. It demonstrated, however, the need for higher-order corrections of the trace formula. The application of a curvature correction to the Fresnel reflection coefficients entering the trace formula yielded better agreement, but deviations remained, indicating the necessity of further investigations.Fri, 13 Feb 2015 14:38:37 GMTFidelity for kicked atoms with gravity near a quantum resonance
http://hdl.handle.net/2268/178319
Title: Fidelity for kicked atoms with gravity near a quantum resonance
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<br/>Author, co-author: Dubertrand, Rémy; Guarneri, I; Wimberger, S
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<br/>Abstract: Kicked atoms under a constant Stark or gravity field are investigated for experimental setups with cold and ultracold atoms. The parametric stability of the quantum dynamics is studied using the fidelity. In the case of a quantum resonance, it is shown that the behavior of the fidelity depends on arithmetic properties of the gravity parameter. Close to a quantum resonance, the long-time asymptotics of the fidelity is studied by means of a pseudoclassical approximation introduced by Fishman et al. [J. Stat. Phys. 110, 911 (2003)]. The long-time decay of fidelity arises from the tunneling out of pseudoclassical stable islands, and a simple ansatz is proposed
which satisfactorily reproduces the main features observed in numerical simulations.Fri, 13 Feb 2015 14:34:39 GMTTrace formula for dielectric cavities. II. Regular, pseudointegrable, and chaotic examples
http://hdl.handle.net/2268/178318
Title: Trace formula for dielectric cavities. II. Regular, pseudointegrable, and chaotic examples
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<br/>Author, co-author: Bogomolny, E; Djellali, N; Dubertrand, Rémy; Gozhyk, I; Lebental, M; Schmit, C; Ulysse, C; Zyss, J
<br/>
<br/>Abstract: Dielectric resonators are open systems particularly interesting due to their wide range of applications in optics and photonics. In a recent paper [Phys. Rev. E 78, 056202 (2008)] the trace formula for both the smooth and the oscillating parts of the resonance density was proposed and checked for the circular cavity. The present paper deals with numerous shapes which would be integrable (square, rectangle, and ellipse), pseudointegrable (pentagon), and chaotic (stadium), if the cavities were closed (billiard case). A good agreement is found between
the theoretical predictions, the numerical simulations, and experiments based on organic microlasers.Fri, 13 Feb 2015 14:29:25 GMTFidelity of the near-resonant quantum kicked rotor
http://hdl.handle.net/2268/178317
Title: Fidelity of the near-resonant quantum kicked rotor
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<br/>Author, co-author: Probst, B; Dubertrand, Rémy; Wimberger, S.
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<br/>Abstract: We present a perturbative result for the temporal evolution of the fidelity of the quantum kicked rotor, i.e. the overlap of the same initial state evolved with two slightly different kicking strengths, for kicking periods close to a principal quantum resonance. Based on a pendulum approximation, we describe the fidelity for rotational orbits in the pseudo-classical phase space of a corresponding classical map. Our results are compared to numerical simulations indicating the range of applicability of our analytical approximation.Fri, 13 Feb 2015 14:24:25 GMTNear integrable systems
http://hdl.handle.net/2268/178314
Title: Near integrable systems
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<br/>Author, co-author: Bogomolny, E.; Dennis, M. R.; Dubertrand, Rémy
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<br/>Abstract: A two-dimensional circular quantum billiard with unusual boundary conditions
introduced by Berry and Dennis (2008 J. Phys. A: Math. Theor. 41 135203)
is considered in detail. It is demonstrated that most of its eigenfunctions are
strongly localized and the corresponding eigenvalues are close to eigenvalues
of the circular billiard with Neumann boundary conditions. Deviations from
strong localization are also discussed. These results agree well with numerical
calculations.Fri, 13 Feb 2015 14:11:27 GMTTrace formula for dielectric cavities: General properties
http://hdl.handle.net/2268/178313
Title: Trace formula for dielectric cavities: General properties
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<br/>Author, co-author: Bogomolny, E.; Dubertrand, Rémy; Schmit, C
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<br/>Abstract: The construction of the trace formula for open dielectric cavities is examined in detail. Using the Krein formula it is shown that the sum over cavity resonances can be written as a sum over classical periodic orbits for the motion inside the cavity. The contribution of each periodic orbit is the product of the two factors. The first is the same as in the standard trace formula and the second is connected with the product of reflection coefficients for all points of reflection with the cavity boundary. Two asymptotic terms of the smooth resonance counting function related with the area and the perimeter of a convex cavity are derived. The coefficient of the perimeter term differs from the one for closed cavities due to unusual high-energy asymptotics of the S matrix for the scattering on the cavity. Corrections to the leading semi-classical formula are briefly discussed. Obtained formulas agree well with numerical calculations for circular dielectric cavities.Fri, 13 Feb 2015 14:02:59 GMTCircular dielectric cavity and its deformation
http://hdl.handle.net/2268/178311
Title: Circular dielectric cavity and its deformation
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<br/>Author, co-author: Dubertrand, Rémy; Bogomolny, E; Djellali, N; Lebental, M; Schmit, C
<br/>
<br/>Abstract: The construction of perturbation series for slightly deformed dielectric circular cavity is discussed in detail. The obtained formulas are checked on the example of cut disks. A good agreement is found with direct numerical simulations and far-field experiments.Fri, 13 Feb 2015 13:58:05 GMTInferring periodic orbits from spectra of simply shaped microlasers
http://hdl.handle.net/2268/178310
Title: Inferring periodic orbits from spectra of simply shaped microlasers
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<br/>Author, co-author: Lebental, M; Djellali, N; Arnaud, C; Lauret, J.-S.; Zyss, J.; Dubertrand, Rémy; Schmit, C.; Bogomolny, E.
<br/>
<br/>Abstract: Dielectric microcavities are widely used as laser resonators and characterizations of their spectra are of interest for various applications. We experimentally investigate microlasers of simple shapes ͑Fabry-Perot, square, pentagon, and disk͒. Their lasing spectra consist mainly of almost equidistant peaks and the distance between peaks reveals the length of a quantized periodic orbit. To measure this length with a good precision, it is necessary to take into account different sources of refractive index dispersion. Our experimental and numerical results agree with the superscar model describing the formation of long-lived states in polygonal cavities. The limitations of the two-dimensional approximation are briefly discussed in connection with
microdisks.Fri, 13 Feb 2015 13:50:06 GMTSLE description of the nodal lines of random wavefunctions
http://hdl.handle.net/2268/178308
Title: SLE description of the nodal lines of random wavefunctions
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<br/>Author, co-author: Bogomolny, E.; Dubertrand, Rémy; Schmit, C.
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<br/>Abstract: The nodal lines of random wavefunctions are investigated. We demonstrate
numerically that they are well approximated by the so-called SLE 6 curves
which describe the continuum limit of the percolation cluster boundaries. This
result gives additional support to the recent conjecture that the nodal domains of
random (and chaotic) wavefunctions in the semi-classical limit are adequately
described by the critical percolation theory. It is also shown that using the
dipolar variant of SLE reduces significantly finite size effects.Fri, 13 Feb 2015 13:47:17 GMT