| 1. |
- Bergkvist, Sara, et al.
(author)
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Transition from a two-dimensional superfluid to a one-dimensional mott insulator
- 2007
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 99:11, s. 110401-1-110401-5
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Journal article (peer-reviewed)abstract
- A two-dimensional system of atoms in an anisotropic optical lattice is studied theoretically. If the system is finite in one direction, it is shown to exhibit a transition between a two-dimensional superfluid and a one-dimensional Mott insulating chain of superfluid tubes. Monte Carlo simulations are consistent with the expectation that the phase transition is of Kosterlitz-Thouless type. The effect of the transition on experimental time-of-flight images is discussed.
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| 2. |
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| 3. |
- Bezett, Alice, et al.
(author)
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Temporal correlations of elongated Bose gases at finite temperature
- 2012
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In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 45:20, s. 205301-
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Journal article (peer-reviewed)abstract
- Temporal correlations in the harmonically trapped finite-temperature Bose gas are studied through the calculation of appropriate phase correlation functions. A wide parameter regime is covered to ascertain the role that temperature fluctuations and trap geometry play in the temporal coherence of the 1D to 3D crossover region. Bogoliubov analysis is used to establish results in the 1D and spherical limits. Formalism is then developed using the projected Gross-Pitaevskii equation to calculate correlation functions in 3D simulations of varying trap elongation and temperature.
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| 4. |
- Cetoli, Alberto, 1979-, et al.
(author)
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Correlations and superfluidity of a one-dimensional Bose gas in a quasiperiodic potential
- 2010
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 81:6, s. 063635-063642
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Journal article (peer-reviewed)abstract
- We consider the correlations and superfluid properties of a Bose gas in an external potential. Using a Bogoliubov scheme, we obtain expressions for the correlation function and the superfluid density in an arbitrary external potential. These expressions are applied to a one-dimensional system at zero temperature subject to a quasiperiodic modulation. The critical parameters for the Bose glass transition are obtained using two different criteria and the results are compared. The Lifshitz glass is seen to be the limiting case for vanishing interactions.
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| 5. |
- Cetoli, Alberto, 1979-
(author)
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Excitations in Superfluids : From solitons to gravitational waves
- 2011
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Doctoral thesis (other academic/artistic)abstract
- In 1995 two different research groups observed for the first time the Bose-Einstein condensation (BEC) in ultracold gases. When the confining magnetic trap was turned off the gas was left free to expand, and the velocity of the particles showed a clear peak: most of the particles were occupying the same single particle state, the one of lowest energy. The Bose-Einstein condensation had been predicted in 1925 by Einstein, written by inspiration of a work on the statistic of the photons by Bose (1924). In this work Bose described the behavior of an ensemble of photons, treating them as massless particles, with no number conservation associated. Einstein extended this approach to particles with a mass and with fixed number, creating what is now called the Bose-Einstein distribution. The particles that follow such a description are called ``bosons'', as opposed to the ``fermions'' of the Fermi-Dirac statistics. Einstein predicted that in a gas of bosons - under a critical temperature - a finite fraction of the total number of particles would have been in the ground state, and act as a single entity. This amusing theoretical discovery found its utility a few years later. In the late thirties, new techniques allowed to cool Helium-4 at few Kelvins above the absolute zero. The properties of the resulting liquid were a puzzlement to the scientific community: among others, it could flow without experiencing friction. The liquid was called a ``superfluid''. A first explanation was given by London in 1938, which linked the superfluid behavior to the presence of a BEC among the bosonic Helium particles. The fermions cannot condense by themselves. On the other hand, they can form bound pairs and act as bosons, as it happens in a metal at low temperature. Using this approach, in 1957 Bardeen, Cooper and Schrieffer created a successful model of superconductivity by describing a superconductor as a superfluid in a charged system. During the course of these years we explored the superfluid properties of Bosons and Fermions in different settings. The original contributions of the thesis are described starting from the third chapter, where we speak about the generation and stability of solitons in a periodic optical lattices, both fixed or in motion. In the fourth chapter we study the generation of giant vortices in cold fermions, by using a generalized hydrodynamical approach. In chapter 5 we study the effect of a quasiperiodic lattice and the glassy phase it produces on a gas of bosons. Finally, we study the interaction of normal matter and superfluids with gravitational waves. While this interaction is seen to be extremely small, we believe that the resulting formalism is interesting by itself.
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| 6. |
- Cetoli, Alberto, et al.
(author)
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Loss of coherence and superfluid depletion in an optical quasicrystal
- 2013
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In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:8, s. 085302-
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Journal article (peer-reviewed)abstract
- We study numerically a 2D Bose-Einstein condensate in a quasiperiodic array of potential peaks, assumed to be generated by superimposing five blue detuned laser beams. By using a Bogoliubov ansatz we show that the system experiences a loss of coherence and starts developing a normal part. We give estimates where a phase transition to an insulating phase should happen for the use of future experiments, along with a study of the validity of the Bogoliubov approximation.
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| 7. |
- Cetoli, Alberto, 1979-, et al.
(author)
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Re-entrant transition of bosons in a quasiperiodic potential
- 2010
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In: European Physics Letters. - : IOP Publishing. ; 90:4, s. 46001-46005
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Journal article (peer-reviewed)abstract
- We investigate the behavior of a two-dimensional array of Bose-Einstein condensate tubes described by means of a Bose-Hubbard Hamiltonian. Using a Wannier function expansion for the wave function in each tube, we compute the Bose-Hubbard parameters related to two different longitudinal potentials, periodic and quasiperiodic. We predict that—upon increasing the external potential strength along the direction of the tubes—the system can experience a re-entrant transition between a Mott insulating phase and the superfluid one.
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| 8. |
- Collin, A, et al.
(author)
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Center-of-mass rotation and vortices in an attractive Bose gas
- 2005
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 71:2, s. 023613-
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Journal article (peer-reviewed)abstract
- The rotational properties of an attractively interacting Bose gas are studied using analytical and numerical methods. We study perturbatively the ground-state phase space for weak interactions, and find that in an anharmonic trap the rotational ground states are vortex or center-of-mass rotational states; the crossover line separating these two phases is calculated. We further show that the Gross-Pitaevskii equation is a valid description of such a gas in the rotating frame and calculate numerically the phase-space structure using this equation. It is found that the transition between vortex and center-of-mass rotation is gradual; furthermore, the perturbative approach is valid only in an exceedingly small portion of phase space. We also present an intuitive picture of the physics involved in terms of correlated successive measurements for the center-of-mass state.
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| 9. |
- Jackson, A D, et al.
(author)
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Phase diagram of a rotating Bose-Einstein condensate with anharmonic confinement
- 2004
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 69:5, s. 053619-
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Journal article (peer-reviewed)abstract
- We examine the phase diagram of an effectively repulsive Bose-Einstein condensate of atoms that rotates in a quadratic-plus-quartic potential. With use of a variational method we identify the three possible phases of the system as a function of the rotational frequency of the trap and of the coupling constant. The derived phase diagram is shown to be universal and partly exact in the limit of weak interactions and small anharmonicity. The variational results are found to be consistent with numerical solutions of the Gross-Pitaevskii equation.
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| 10. |
- Jackson, A D, et al.
(author)
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Stability of the solutions of the Gross-Pitaevskii equation
- 2005
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 72:5, s. 053617-
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Journal article (peer-reviewed)abstract
- We examine the static and dynamic stability of the solutions of the Gross-Pitaevskii equation and demonstrate the intimate connection between them. All salient features related to dynamic stability are reflected systematically in static properties. We find, for example, the obvious result that static stability always implies dynamic stability and present a simple explanation of the fact that dynamic stability can exist even in the presence of static instability.
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