Mikkel Andersen

Weizmann Institute of Science, Israel

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Publications (13)40.4 Total impact

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    M F Andersen, A Kaplan, T Grünzweig, N Davidson
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    ABSTRACT: We perform echo spectroscopy on ultracold atoms in atom-optics billiards to study their quantum dynamics. The detuning of the trapping laser is used to change the "perturbation", which causes a decay in the echo coherence. Two different regimes are observed: first, a perturbative regime in which the decay of echo coherence is nonmonotonic and partial revivals of coherence are observed in contrast with the predictions of random matrix theory. These revivals are more pronounced in traps with mixed dynamics as compared to traps where the dynamics is fully chaotic. Next, for stronger perturbations, the decay becomes monotonic and independent of the strength of the perturbation. In this regime no clear distinction can be made between chaotic traps and traps with mixed dynamics.
    Physical Review Letters 10/2006; 97(10):104102. DOI:10.1103/PhysRevLett.97.104102 · 7.73 Impact Factor
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    A Kaplan, M F Andersen, T Grünzweig, N Davidson
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    ABSTRACT: We perform spectroscopy on the ground-state hyperfine splitting of 85 Rb atoms trapped in far-off-resonance optical traps. The existence of a spatially dependent shift in the energy levels is shown to induce an inherent dephasing effect, which causes a broadening of the spectroscopic line and hence an inhomogeneous loss of atomic coherence at a much faster rate than the homogeneous one caused by spontaneous photon scattering. We present here a number of approaches for reducing this inhomogeneous broadening, based on trap geometry, additional laser fields, and novel microwave pulse sequences. We then show how hyperfine spectroscopy can be used to study the quantum dynamics of optically trapped atoms.
    Journal of Optics A Pure and Applied Optics 07/2005; 7:103-125. DOI:10.1088/1464-4266/7/8/R01 · 1.92 Impact Factor
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    ABSTRACT: We developed a new experimental system (the “atom-optics billiard”) and demonstrated chaotic and regular dynamics of cold, optically trapped atoms. We show that the softness of the walls and additional optical potentials can be used to manipulate the structure of phase space.
    12/2004: pages 239-267;
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    ABSTRACT: We present a new experimental system (the ``atom-optics billiard'') and demonstrate chaotic and regular dynamics of cold, optically trapped atoms. We show that the softness of the walls and additional optical potentials can be used to manipulate the structure of phase space.
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    ABSTRACT: The decay in the hyperfine coherence of optically trapped atoms due to interactions with the environment, is only partly suppressed by "echo" spectroscopy [ M. F. Andersen Phys. Rev. Lett. 90, 023001 (2003) ], primarily due to dynamical (time-dependent) dephasing mechanisms. We demonstrate here an improved pulse sequence, for which the decay of coherence is reduced by a factor of 2.5 beyond the reduction offered by the "echo" spectroscopy. This reduction occurs when each dark period in-between pulses is shorter than the time scale over which substantial dephasing develops. The coherence time is then limited by mixing to other vibrational levels in the trap and, to a lesser extent, the lifetime of the internal states of the atoms.
    Physical Review A 07/2004; 70(1):013405. DOI:10.1103/PhysRevA.70.013405 · 2.99 Impact Factor
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    ABSTRACT: The loss in coherence in a trapped-atoms "echo" experiment is suppressed by a different pulse sequence. The coherence time is then limited by mixing to other vibrational levels and the lifetime of the internal states
    Quantum Electronics Conference, 2004. (IQEC). International; 06/2004
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    ABSTRACT: We investigate the coherence properties of thermal atoms confined in optical dipole traps where the under-lying classical dynamics is chaotic. A perturbative expression derived for the coherence of the echo scheme of Anderson et al. [Phys. Rev. Lett. 90, 023001 (2003)] shows that it is a function of the survival probability or fidelity of eigenstates of the motion of the atoms in the trap. The echo coherence and the survival probability display "system specific" features, even when the underlying classical dynamics is chaotic. In particular, partial revivals in the echo signal and the survival probability are found for a small shift of the potential. Next, a "semiclassical" expression for the averaged echo signal is presented and used to calculate the echo signal for atoms in a light sheet wedge billiard. Revivals in the echo coherence are found in this system, indicating that they may be a generic feature of dipole traps.
    Physical Review A 06/2004; 69(6):063413. DOI:10.1103/PhysRevA.69.063413 · 2.99 Impact Factor
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    M F Andersen, A Kaplan, N Davidson
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    ABSTRACT: We investigate the dephasing of ultra cold 85Rb atoms trapped in an optical dipole trap and prepared in a coherent superposition of their two hyperfine ground states by interaction with a microwave pulse. We demonstrate that the dephasing, measured as the Ramsey fringe contrast, can be reversed by stimulating a coherence echo with a pi pulse between the two pi / 2 pulses, in analogy to the photon echo. We also demonstrate that "echo spectroscopy" can be used to study the quantum dynamics in the trap even when more than 10(6) states are thermally populated and to study the crossover from quantum to classical dynamics.
    Physical Review Letters 02/2003; 90(2):023001. DOI:10.1103/PhysRevLett.90.023001 · 7.73 Impact Factor
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    M. F. Andersen, A. Kaplan, T. Grünzweig, N Davidson
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    ABSTRACT: We discuss a recently demonstrated type of microwave spectroscopy of trapped ultra-cold atoms known as "echo spectroscopy" [M.F. Andersen et. al., Phys. Rev. Lett., in press (2002)]. Echo spectroscopy can serve as an extremely sensitive experimental tool for investigating quantum dynamics of trapped atoms even when a large number of states are thermally populated. We show numerical results for the stability of eigenstates of an atom-optics billiard of the Bunimovich type, and discuss its behavior under different types of perturbations. Finally, we propose to use special geometrical constructions to make a dephasing free dipole trap.
    Communications in Nonlinear Science and Numerical Simulation 12/2002; DOI:10.1016/S1007-5704(03)00029-7 · 2.57 Impact Factor
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    Ariel Kaplan, Mikkel Fredslund Andersen, Nir Davidson
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    ABSTRACT: We present a novel method for reducing the inhomogeneous frequency broadening in the hyperfine splitting of the ground state of optically trapped atoms. This reduction is achieved by the addition of a weak light field, spatially mode-matched with the trapping field and whose frequency is tuned in-between the two hyperfine levels. We experimentally demonstrate the new scheme with Rb 85 atoms, and report a 50-fold narrowing of the rf spectrum.
    Physical Review A 10/2002; 66:045401. DOI:10.1103/PhysRevA.66.045401 · 2.99 Impact Factor
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    M F Andersen, A Kaplan, N Friedman, N Davidson
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    ABSTRACT: We investigate the effects of curving trajectories by applying external force fields on a particle in a billiard. We investigate two special cases: a constant force field and a parabolic potential. These perturbations change the stability conditions and can lead to formation of elliptical orbits in otherwise hyperbolic billiards. We demonstrate these effects experimentally with ultra-cold atoms in atom-optic billiards.
    Journal of Physics B Atomic Molecular and Optical Physics 04/2002; 35(9):2183. DOI:10.1088/0953-4075/35/9/315 · 1.92 Impact Factor
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    ABSTRACT: We present numerical and experimental results for the development of islands of stability in atom-optics billiards with soft walls. As the walls are soften, stable regions appear near singular periodic trajectories in converging (focusing) and dispersing billiards, and are surrounded by areas of “stickiness” in phase space. The size of these islands depends on the softness of the potential in a very sensitive way.
    Physica D Nonlinear Phenomena 01/2002; DOI:10.1016/j.physd.2003.09.010 · 1.83 Impact Factor
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    ABSTRACT: We report on numerical and experimental observations of islands of stability induced in a Bunimovich stadium atom-optics billiard by a soft wall repulsive potential. A deviation from exponential decay of the survival probability of atoms in an open billiard is observed, and explained by the presence of these stable islands and a sticky region surrounding them. We also investigate islands in dispersing billiards with soft walls, and predict a new mechanism for their formation.
    Physical Review Letters 01/2002; 87(27 Pt 1):274101. DOI:10.1103/PhysRevLett.87.274101 · 7.73 Impact Factor