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Search Results: 1 - 10 of 297550 matches for " J. Kajala "
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Collision of one dimensional (1D) spin polarized Fermi gases in an optical lattice
J. Kajala,F. Massel,And P. T?rm?
Physics , 2011, DOI: 10.1140/epjd/e2011-20081-8
Abstract: In this work we analyze the dynamical behavior of the collision between two clouds of fermionic atoms with opposite spin polarization. By means of the time-evolving block decimation (TEBD) numerical method, we simulate the collision of two one-dimensional clouds in a lattice. There is a symmetry in the collision behaviour between the attractive and repulsive interactions. We analyze the pair formation dynamics in the collision region, providing a quantitative analysis of the pair formation mechanism in terms of a simple two-site model.
Expansion dynamics of the Fulde-Ferrell-Larkin-Ovchinnikov state
J. Kajala,F. Massel,P. Torma
Physics , 2011, DOI: 10.1103/PhysRevA.84.041601
Abstract: We consider a two-component Fermi gas in the presence of spin imbalance, modeling the system in terms of a one-dimensional attractive Hubbard Hamiltonian initially in the presence of a confining trap potential. With the aid of the time-evolving block decimation method, we investigate the dynamics of the initial state when the trap is switched off. We show that the dynamics of a gas initially in the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state is decomposed into the independent expansion of two fluids, namely the paired and the unpaired particles. In particular, the expansion velocity of the unpaired cloud is shown to be directly related to the FFLO momentum. This provides an unambiguous signature of the FFLO state in a remarkably simple way.
Expansion dynamics in the one-dimensional Fermi-Hubbard model
J. Kajala,F. Massel,P. T?rm?
Physics , 2011, DOI: 10.1103/PhysRevLett.106.206401
Abstract: Expansion dynamics of interacting fermions in a lattice are simulated within the one-dimensional (1D) Hubbard model, using the essentially exact time-evolving block decimation (TEBD) method. In particular, the expansion of an initial band-insulator state is considered. We analyze the simulation results based on the dynamics of a two-site two-particle system, the so-called Hubbard dimer. Our findings describe essential features of a recent experiment on the expansion of a Fermi gas in a two-dimensional lattice. We show that the Hubbard-dimer dynamics, combined with a two-fluid model for the paired and non-paired components of the gas, gives an efficient description of the full dynamics. This should be useful for describing dynamical phenomena of strongly interacting Fermions in a lattice in general.
Resonant scattering effect in spectroscopies of interacting atomic gases
M. J. Leskinen,J. Kajala,J. J. Kinnunen
Physics , 2009, DOI: 10.1088/1367-2630/12/8/083041
Abstract: We consider spectroscopies of strongly interacting atomic gases, and we propose a model for describing the coupling between quasiparticles and gapless phonon-like modes. Our model explains features in a wide range of different experiments in both fermionic and bosonic atom gases in various spectroscopic methods.
Quasiparticles, coherence and nonlinearity: exact simulations of RF-spectroscopy of strongly interacting one-dimensional Fermi gases
M. J. Leskinen,V. Apaja,J. Kajala,P. Torma
Physics , 2008, DOI: 10.1103/PhysRevA.78.023602
Abstract: We consider RF-spectroscopy of ultracold Fermi gases by exact simulations of the many-body state and the coherent dynamics in one dimension. Deviations from the linear response sum rule result are found to suppress the pairing contribution to the RF line shifts. We compare the coherent rotation and quasiparticle descriptions of RF-spectroscopy which are analogous to NMR experiments in superfluid $^3$He and tunneling in solids, respectively. We suggest that RF-spectroscopy in ultracold gases provides an interesting crossover between these descriptions that could be used for studying decoherence in quantum measurement, in the context of many-body quantum states.
Spin-asymmetric Josephson effect
M. O. J. Heikkinen,F. Massel,J. Kajala,M. J. Leskinen,G. -S. Paraoanu,P. Torma
Physics , 2009, DOI: 10.1103/PhysRevLett.105.225301
Abstract: The Josephson effect is a manifestation of the macroscopic phase coherence of superconductors and superfluids. We propose that with ultracold Fermi gases one can realise a spin-asymmetric Josephson effect in which the two spin components of a Cooper pair are driven asymmetrically - corresponding to driving a Josephson junction of two superconductors with different voltages V_\uparrow and V_\downarrow for spin up and down electrons, respectively. We predict that the spin up and down components oscillate at the same frequency but with different amplitudes. Our results reveal that the standard description of the Josephson effect in terms of bosonic pair tunnelling is insufficient. We provide an intuitive interpretation of the Josephson effect as interference in Rabi oscillations of pairs and single particles, the latter causing the asymmetry.
New components of the mercury’s perihelion precession  [PDF]
J. J. Smulsky
Natural Science (NS) , 2011, DOI: 10.4236/ns.2011.34034
Abstract: The velocity of perihelion rotation of Mercury's orbit relatively motionless space is computed. It is prove that it coincides with that calculated by the Newtonian interaction of the planets and of the compound model of the Sun’s rotation.
Simple General Purpose Ion Beam Deceleration System Using a Single Electrode Lens  [PDF]
J. Lopes, J. Rocha
World Journal of Engineering and Technology (WJET) , 2015, DOI: 10.4236/wjet.2015.33014
Abstract: Ion beam deceleration properties of a newly developed low-energy ion beam implantation system were studied. The objective of this system was to produce general purpose low-energy (5 to 15 keV) implantations with high current beam of hundreds of μA level, providing the most wide implantation area possible and allowing continuously magnetic scanning of the beam over the sample(s). This paper describes the developed system installed in the high-current ion implanter at the Laboratory of Accelerators and Radiation Technologies of the Nuclear and Technological Cam-pus, Sacavém, Portugal (CTN).
Constraints on velocity anisotropy of spherical systems with separable augmented densities
J. An
Physics , 2011, DOI: 10.1088/0004-637X/736/2/151
Abstract: If the augmented density of a spherical anisotropic system is assumed to be multiplicatively separable to functions of the potential and the radius, the radial function, which can be completely specified by the behavior of the anisotropy parameter alone, also fixes the anisotropic ratios of every higher-order velocity moment. It is inferred from this that the non-negativity of the distribution function necessarily limits the allowed behaviors of the radial function. This restriction is translated into the constraints on the behavior of the anisotropy parameter. We find that not all radial variations of the anisotropy parameter satisfy these constraints and thus that there exist anisotropy profiles that cannot be consistent with any separable augmented density.
On the augmented density of a spherical anisotropic dynamic system
J. An
Physics , 2010, DOI: 10.1111/j.1365-2966.2011.18324.x
Abstract: This paper presents a set of new conditions on the augmented density of a spherical anisotropic system that is necessary for the underlying two-integral phase-space distribution function to be non-negative. In particular, it is shown that the partial derivatives of the Abel transformations of the augmented density must be non-negative. Applied for the separable augmented densities, this recovers the result of van Hese et al. (2011).
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