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Search Results: 1 - 10 of 306901 matches for " J. J. Garcia-Ripoll "
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Fragmented superfluid due to frustration of cold atoms in optical lattices
J. J. Garcia-Ripoll,J. Pachos
Physics , 2006, DOI: 10.1088/1367-2630/9/5/139
Abstract: A one dimensional optical lattice is considered where a second dimension is encoded in the internal states of the atoms giving effective ladder systems. Frustration is introduced by an additional optical lattice that induces tunneling of superposed atomic states. The effects of frustration range from the stabilization of the Mott insulator phase with ferromagnetic order, to the breakdown of superfluidity and the formation of a macroscopically fragmented phase.
Dynamical creation of bosonic Cooper-like pairs
T. Keilmann,J. J. Garcia-Ripoll
Physics , 2007, DOI: 10.1103/PhysRevLett.100.110406
Abstract: We propose a scheme to create a metastable state of paired bosonic atoms in an optical lattice. The most salient features of this state are that the wavefunction of each pair is a Bell state and that the pair size spans half the lattice, similar to fermionic Cooper pairs. This mesoscopic state can be created with a dynamical process that involves crossing a quantum phase transition and which is supported by the symmetries of the physical system. We characterize the final state by means of a measurable two-particle correlator that detects both the presence of the pairs and their size.
The moment method in general Nonlinear Schrodinger Equations
J. J. Garcia-Ripoll,V. M. Perez-Garcia
Physics , 1999,
Abstract: In this paper we develop a new approximation method valid for a wide family of nonlinear wave equations of Nonlinear Schr\"odinger type. The result is a reduced set of ordinary differential equations for a finite set of parameters measuring global properties of the solutions, named momenta. We prove that these equations provide exact results in some relevant cases and show how to impose reasonable approximations that can be regarded as a perturbative approach and as an extension of the time dependent variational method.
Nucleation of bended vortices in Bose-Einstein condensates in elongated traps
J. J. Garcia-Ripoll,V. M. Perez-Garcia
Physics , 2000,
Abstract: We study the generation of vortices in rotating axially elongated magneto-optical traps, a situation which has been realized in a recent experiment (K. W. Madison, F. Chevy, W. Wohlleben, J. Dalibard, Phys. Rev. Lett. 84, 806 (2000)). We predict that at a critical frequency the condensate experiences a symmetry breaking and changes from a convex cloud to a state with one bended vortex. We also discuss several effects which enlarge the critical frequency with respect to other geometries of the trap: these are, (i) the failure of the Thomas-Fermi approximation on the transverse degrees of freedom of the condensate, (ii) the enhancement of the transverse asymmetry of the trap by means of rotation and (iii) the yet unobserved bending of the vortex lines.
Anomalous rotational properties of Bose-Einstein condensates in asymmetric traps
J. J. Garcia-Ripoll,V. M. Perez-Garcia
Physics , 2000, DOI: 10.1103/PhysRevA.64.013602
Abstract: We study the rotational properties of a Bose-Einstein condensate confined in a rotating harmonic trap for different trap anisotropies. Using simple arguments, we derive expressions for the velocity field of the quantum fluid for condensates with or without vortices. While the condensed gas describes open spiraling trajectories, on the frame of reference of the rotating trap the motion of the fluid is against the trap rotation. We also find explicit formulae for the angular momentum and a linear and Thomas-Fermi solutions for the state without vortices. In these two limits we also find an analytic relation between the shape of the cloud and the rotation speed. The predictions are supported by numerical simulations of the mean field Gross-Pitaevskii model.
Barrier resonances in Bose-Einstein condensation
J. J. Garcia-Ripoll,V. M. Perez-Garcia
Physics , 1998, DOI: 10.1103/PhysRevA.59.2220
Abstract: We study the dynamics of the mean field model of a Bose-Einstein condensed atom cloud in a parametrically forced trap by using analytical and numerical techniques. The dynamics is related to a classical Mathieu oscillator in a singular potential. It is found that there are wide resonances which can strongly affect the dynamics even when dissipation is present. Different geometries of the forcing are discussed, as well as the implications of our results.
Vortex bending and tightly packed vortex lattices in Bose-Einstein condensates
J. J. Garcia-Ripoll,V. M. Perez-Garcia
Physics , 2001, DOI: 10.1103/PhysRevA.64.053611
Abstract: We study in detail the counterintuitive result that in elongated rotating Bose--Einstein condensates the ground state is composed of one or more vortex lines which bend even in completely symmetric setups. This symmetry breaking allows the condensate to smoothly adapt to rotation and to produce tightly packed arrays of vortex lines.
Stability of vortices in rotating taps: a 3d analysis
J. J. Garcia-Ripoll,V. M. Perez-Garcia
Physics , 1999, DOI: 10.1103/PhysRevA.60.4864
Abstract: We study the stability of vortex-lines in trapped dilute gases subject to rotation. We solve numerically both the Gross-Pitaevskii and the Bogoliubov equations for a 3d condensate in spherically and cilyndrically symmetric stationary traps, from small to very large nonlinearities. In the stationary case it is found that the vortex states with unit and $m=2$ charge are energetically unstable. In the rotating trap it is found that this energetic instability may only be suppressed for the $m=1$ vortex-line, and that the multicharged vortices are never a local minimum of the energy functional, which implies that the absolute minimum of the energy is not an eigenstate of the $L_z$ operator, when the angular speed is above a certain value, $\Omega > \Omega_2$.
Quantum computation with unknown parameters
J. J. Garcia-Ripoll,J. I. Cirac
Physics , 2002, DOI: 10.1103/PhysRevLett.90.127902
Abstract: We show how it is possible to realize quantum computations on a system in which most of the parameters are practically unknown. We illustrate our results with a novel implementation of a quantum computer by means of bosonic atoms in an optical lattice. In particular we show how a universal set of gates can be carried out even if the number of atoms per site is uncertain.
Coherent control of trapped ions using off-resonant lasers
J. J. Garcia-Ripoll,P. Zoller,J. I. Cirac
Physics , 2004, DOI: 10.1103/PhysRevA.71.062309
Abstract: In this paper we develop a unified framework to study the coherent control of trapped ions subject to state-dependent forces. Taking different limits in our theory, we can reproduce two different designs of a two-qubit quantum gate --the pushing gate [1] and the fast gates based on laser pulses from Ref. [2]--, and propose a new design based on continuous laser beams. We demonstrate how to simulate Ising Hamiltonians in a many ions setup, and how to create highly entangled states and induce squeezing. Finally, in a detailed analysis we identify the physical limits of this technique and study the dependence of errors on the temperature. [1] J.I. Cirac, P. Zoller, Nature, 404, 579, 2000. [2] J.J. Garcia-Ripoll, P. Zoller, J.I. Cirac, PRL 67, 062318, 2003
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