Publications (36)100.58 Total impact
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Chapter: New generation of light sources for applications in spectroscopy
05/2007: pages 245-256; -
Article: Collective excitations of a 87Rb Bose condensate in the Thomas-Fermi regime
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ABSTRACT: Collective excitations have been observed in a 87Rb Bose condensate, confined in a magneto-static, elongated, harmonic trap. We have measured the frequency of two different modes with zero angular momentum along the symmetry axis of the trap. Both the frequencies are in good agreement with the values predicted by the hydrodynamic theory of superfluids holding in the Thomas-Fermi regime.EPL (Europhysics Letters) 01/2007; 49(1):8. · 2.17 Impact Factor -
Article: Coherence Effects in Cold Cesium Atoms
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ABSTRACT: We have studied a ladder and a Λ system on cold Cesium atoms released from a magneto optical trap. Probe absorption spectra have been satisfactorily interpreted in terms of a non degenerate three level model at low pump power. At higher power a sum of non interacting three level systems is adequate to predict line positions. An experimental test for a sum rule in nonlinear optics is presented and a novel type of dark trap that relies on electromagnetically induced transparency for a velocity selective storage in the dark state is demonstrated.Physica Scripta 11/2006; 1998(T78):19. · 1.20 Impact Factor -
Article: From superradiant Rayleigh scattering to Bragg scattering
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ABSTRACT: We present the results of an experiment on light scattering from an elongated Bose-Einstein condensate interacting with far off resonant laser light. Due to superradiant Rayleigh scattering a coherent superposition of two atomic wavepackets with different momenta forms in the presence of a single laser beam. Varying the intensity of a weak counterpropagating laser beam we observe the transition from the pure superradiant regime to the Bragg scattering regime, where Rabi oscillations in a two-level system are observed. The process is limited by the decoherence between the two atomic wavepackets.The European Physical Journal D 01/2005; 32(2):167-170. · 1.48 Impact Factor -
Article: Collective atomic recoil in a moving Bose-Einstein condensate: from superradiance to Bragg scattering
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ABSTRACT: We present the results of an experiment on light scattering from an elongated Bose-Einstein condensate BEC interacting with a far-off-resonant pump laser. By collective atomic recoil lasing CARL a coherent superposition of two atomic wave packets with different momenta is created. Varying the intensity of a weak counterpropagating laser beam we observe the transition from the pure superradiant regime to the Bragg scattering regime, where Rabi oscillations in a two-level system are observed. The process is limited by the decoherence between the two atomic wave packets. In the superradiant regime the experiment gives evidence of a contribution to decoherence which depends on the initial velocity of the condensate. The system is described by the CARL-BEC model, which is a generalization of the Gross-Pitaevskii model to include the self-consistent evolution of the scattered field and a phase-diffusion decoherence process, which accounts for the observed damping.Physical Review A 01/2005; 71:033612. · 2.88 Impact Factor -
Article: Dynamics of bloch matter waves and its breakdown: a bose–einstein condensate in a moving 1d optical lattice
Laser Physics. 12/2004; 15(3):447-453. -
Article: Superradiant light scattering from a moving Bose-Einstein condensate
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ABSTRACT: We investigate the interaction of a moving BEC with a far detuned laser beam. Superradiant Rayleigh scattering arises from the spontaneous formation of a matter-wave grating due to the interference of two wavepackets with different momenta. The system is described by the CARL-BEC model which is a generalization of the Gross-Pitaevskii model to include the self-consistent evolution of the scattered field. The experiment gives evidence of a damping of the matter-wave grating which depends on the initial velocity of the condensate. We describe this damping in terms of a phase-diffusion decoherence process, in good agreement with the experimental results.Optics Communications 01/2004; 233:155. · 1.49 Impact Factor -
Article: Optically induced lensing effect on a Bose-Einstein condensate expanding in a moving lattice.
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ABSTRACT: We report the experimental observation of a lensing effect on a Bose-Einstein condensate expanding in a moving 1D optical lattice. The effect of the periodic potential can be described by an effective mass dependent on the condensate quasimomentum. By changing the velocity of the atoms in the frame of the optical lattice, we induce a focusing of the condensate along the lattice direction. The experimental results are compared with the numerical predictions of an effective 1D theoretical model. In addition, a precise band spectroscopy of the system is carried out by looking at the real-space propagation of the atomic wave packet in the optical lattice.Physical Review Letters 01/2004; 91(24):240405. · 7.37 Impact Factor -
Article: Collective excitations of a trapped Bose-Einstein condensate in the presence of a 1D optical lattice.
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ABSTRACT: We study low-lying collective modes of an elongated 87Rb condensate produced in a 3D magnetic harmonic trap with the addition of a 1D periodic potential which is provided by a laser standing wave along the axial direction. While the transverse breathing mode remains unperturbed, quadrupole and dipole oscillations along the optical lattice are strongly modified. Precise measurements of the collective mode frequencies at different heights of the optical barriers provide a stringent test of the theoretical model recently introduced [M. Krämer, Phys. Rev. Lett. 88, 180404 (2002)]].Physical Review Letters 05/2003; 90(14):140405. · 7.37 Impact Factor -
Article: Dynamics of a trapped Bose–Einstein condensate in the presence of a one-dimensional optical lattice
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ABSTRACT: We explore the dynamics of a Bose–Einstein condensate created in the combined potential of a far-detuned laser standing wave superimposed to a 3D harmonic magnetic potential. We report the investigation of low-lying collective modes showing that the macroscopic dynamics along the optical lattice is strongly modified, resulting in a shift of the dipole and quadrupole mode frequencies depending on the height of the optical lattice, whereas the transverse breathing mode, occurring perpendicularly to the lattice axis, is not perturbed. The experimental findings are compared with the theoretical treatment that generalizes the hydrodynamic equation of superfluids for a weakly interacting Bose gas to include the effects of the periodic potential. We show that the array of condensates trapped in the optical wells and driven by the harmonic magnetic potential is equivalent to an array of Josephson junctions. In the regime of 'small' amplitude dipole oscillation the system performs a collective motion and we investigate the current–phase dynamics measuring the critical Josephson current. Increasing the amplitude of the dipole oscillation, we observe a transition from the coherent oscillation (superfluid regime) to a localization of the condensates in the harmonic trap ('insulator' regime). The onset of the coherent regime breakdown is interpreted as the result of a discrete modulational instability occurring when the velocity of the centre of mass of the system is larger than a critical velocity proportional to the tunnelling rate between adjacent wells.J. Opt. B: Quantum Semiclass. Opt. 01/2003; 5:1464-426655739. -
Article: Superfluid current disruption in a chain of weakly coupled Bose-Einstein condensates
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ABSTRACT: We report the experimental observation of the disruption of the superfluid atomic current flowing through an array of weakly linked Bose-Einstein condensates. The condensates are trapped in an optical lattice superimposed on a harmonic magnetic potential. The dynamical response of the system to a change of the magnetic potential minimum along the optical lattice axis goes from a coherent oscillation (superfluid regime) to a localization of the condensates in the harmonic trap ("classical" insulator regime). The localization occurs when the initial displacement is larger than a critical value or, equivalently, when the velocity of the wavepacket's center of mass is larger than a critical velocity dependent on the tunnelling rate between adjacent sites. Comment: 8 pages, 4 figuresNew Journal of Physics 01/2003; 5:71. · 4.18 Impact Factor -
Article: A Novel Mechanism for Superfluidity Breakdown in Weakly Coupled Bose-Einstein Condensates
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ABSTRACT: This paper has been withdrawn by the authors. The authors have now written two separate papers, one theoretical (A. Smerzi, A. Trombettoni, P. G. Kevrekidis, and A. R. Bishop Phys. Rev. Lett. 89, 170402 (2002)) and one experimental (F. S. Cataliotti, L. Fallani, F. Ferlaino, C. Fort, P. Maddaloni, and M. Inguscio New Journal of Physics 5, 71 (2003)).08/2002; -
Article: Dynamics of a Bose-Einstein condensate at finite temperature in an atomoptical coherence filter
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ABSTRACT: The macroscopic coherent tunneling through the barriers of a periodic potential is used as an atomoptical filter to separate the condensate and the thermal components of a $^{87}$Rb mixed cloud. We condense in the combined potential of a laser standing-wave superimposed on the axis of a cigar-shape magnetic trap and induce condensate dipole oscillation in the presence of a static thermal component. The oscillation is damped due to interaction with the thermal fraction and we investigate the role played by the periodic potential in the damping process.02/2002; -
Article: Bose-Einstein Condensates in a 1D Optical Lattice
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ABSTRACT: We give an overview on current experiments on Bose-Einstein condensation (BEC) in a one-dimensional (1D) optical lattice. We introduce measurements of ground state, tunnelling and dynamical properties as well as investigations of atom optical applications and thermodynamical properties. Measurements of the coherent atomic current in an array of Josephson junctions and the critical velocity for the breakdown of superfluid motion are discussed in detail.12/2001; -
Article: Expansion of a coherent array of Bose-Einstein condensates.
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ABSTRACT: We investigate the properties of a coherent array containing about 200 Bose-Einstein condensates produced in a far detuned 1D optical lattice. The density profile of the gas, imaged after releasing the trap, provides information about the coherence of the ground-state wave function. The measured atomic distribution is characterized by interference peaks. The time evolution of the peaks, their relative population, as well as the radial size of the expanding cloud are in good agreement with the predictions of theory. The 2D nature of the trapped condensates and the conditions required to observe the effects of coherence are also discussed.Physical Review Letters 12/2001; 87(22):220401. · 7.37 Impact Factor -
Article: Dynamics of a Bose-Einstein condensate at finite temperature in an atom-optical coherence filter
Physical Review A. 12/2001; 66(1):11604. -
Article: Superresolution of pulsed multiphoton Raman transitions.
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ABSTRACT: We have investigated higher order multiphoton Raman resonances with two pulsed optical frequencies. Multiphoton transfer with up to 50 photons is observed with milliwatts of laser power. We demonstrate that the spectral width of the multiphoton resonances can be far below the Fourier transform linewidth of the driving optical pulses. The functional dependence of the transition linewidth on the number of exchanged photons is found to vary with the pulse shape. Our experiment is performed with laser-cooled rubidium atoms confined in a CO2-laser optical dipole trap.Physical Review Letters 10/2001; 87(11):113601. · 7.37 Impact Factor -
Article: Josephson junction arrays with Bose-Einstein condensates.
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ABSTRACT: We report on the direct observation of an oscillating atomic current in a one-dimensional array of Josephson junctions realized with an atomic Bose-Einstein condensate. The array is created by a laser standing wave, with the condensates trapped in the valleys of the periodic potential and weakly coupled by the interwell barriers. The coherence of multiple tunneling between adjacent wells is continuously probed by atomic interference. The square of the small-amplitude oscillation frequency is proportional to the microscopic tunneling rate of each condensate through the barriers and provides a direct measurement of the Josephson critical current as a function of the intermediate barrier heights. Our superfluid array may allow investigation of phenomena so far inaccessible to superconducting Josephson junctions and lays a bridge between the condensate dynamics and the physics of discrete nonlinear media.Science 09/2001; 293(5531):843-6. · 31.20 Impact Factor -
Article: Quasi 2D Bose-Einstein condensation in an optical lattice
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ABSTRACT: We study the phase transition of a gas of Rb atoms to quantum degeneracy in the combined potential of a harmonically confining magnetic trap and the periodic potential of an optical lattice. For high optical lattice potentials we observe a significant change in the temperature dependency of the population of the ground state of the system. The experimental results are explained by the subsequent formation of quasi 2D condensates in the single lattice sites. Comment: 7 pages (including 3 figures)08/2001; -
Article: Superfluid and dissipative dynamics of a Bose-Einstein condensate in a periodic optical potential.
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ABSTRACT: We create Bose-Einstein condensates of 87Rb in a static magnetic trap with a superimposed blue-detuned 1D optical lattice. By displacing the magnetic trap center we are able to control the condensate evolution. We observe a change in the frequency of the center-of-mass oscillation in the harmonic trapping potential, in analogy with an increase in effective mass. For fluid velocities greater than a local speed of sound, we observe the onset of dissipative processes up to full removal of the superfluid component. A parallel simulation study visualizes the dynamics of the Bose-Einstein condensate and accounts for the main features of the observed behavior.Physical Review Letters 06/2001; 86(20):4447-50. · 7.37 Impact Factor
Top co-authors
Top Journals
Institutions
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1997–2007
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European Laboratory for Non-Linear Spectroscopy
Florence, Tuscany, Italy
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1996–2004
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Università degli Studi di Firenze
- European Laboratory for Non-Linear Spectroscopy LENS
Florence, Tuscany, Italy
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2000–2001
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Max-Planck-Institut für Quantenoptik
Garching bei München, Bavaria, Germany
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