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Magnetism in systems of ultracold atoms: New problems of quantum many-body dynamics

Magnetism in systems of ultracold atoms: New problems of quantum many-body dynamics. Eugene Demler Harvard University. E. Altman (Weizmann), P. Barmettler (Frieburg), V. Gritsev (Harvard, Freiburg), A. Imambekov (Yale), T. Kitagawa (Harvard), M. Lukin (Harvard),

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Magnetism in systems of ultracold atoms: New problems of quantum many-body dynamics

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  1. Magnetism in systems of ultracold atoms:New problems of quantum many-body dynamics Eugene Demler Harvard University E. Altman (Weizmann), P. Barmettler (Frieburg), V. Gritsev (Harvard, Freiburg), A. Imambekov (Yale), T. Kitagawa (Harvard), M. Lukin (Harvard), S. Pielawa (Harvard), A. Polkovnikov (BU), M. Punk (TU Munich), A.M. Rey (Harvard, CU Boulder, JILA) Collaboration with experimental groups of I. Bloch and J. Schmiedmayer

  2. ? Magnetism in condensed matter systems Ferromagnetismin itinerant systems Many-body magnetism. Equilibrium and ground state Stoner instability. Double exchange Frustrated magnetic systems Antiferromagnetism

  3. 1 t 0 Magnetism in atomic physics Atomic clocks and Ramsey interference Single atom magnetism. Quantum dynamics

  4. Magnetism of ultracold atoms: Quantum many-body dynamics Superexchange and spin dynamics in optical lattices - superexchange interactions in Mott state - observation of superexchange in double wells - spin dynamics of 1d chain Ramsey interference experiments in one dimensional systems - many-body decoherence

  5. Superexchange and spin dynamics in optical lattices

  6. t t Two component Bose mixture in optical lattice Example: . Mandel et al., Nature 425:937 (2003) Two component Bose Hubbard model

  7. Quantum magnetism of bosons in optical lattices • Ferromagnetic • Antiferromagnetic Duan, Demler, Lukin, PRL 91:94514 (2003)

  8. J J Use magnetic field gradient to prepare a state Observe oscillations between and states Observation of superexchange in a double well potential Theory: A.M. Rey et al., PRL 2008 Experiments: S. Trotzky et al. Science 2008

  9. Comparison to the Hubbard model

  10. Beyond the basic Hubbard model Basic Hubbard model includes only local interaction Extended Hubbard model takes into account non-local interaction

  11. Beyond the basic Hubbard model

  12. From two spins to a spin chain ? Spin oscillations

  13. Y(t=0) = Time, Jt 1D: XXZ dynamics starting from the classical Neel state P. Barmettler et al, PRL 2009 Ising-Order Quasi-LRO Equilibrium phase diagram: D 1 • DMRG • XZ model: exact solution

  14. XXZ dynamics starting from the classical Neel state D<1, XY easy plane anisotropy Oscillations of staggered moment, Exponential decay of envelope Except at solvable xx point where: D>1, Z axis anisotropy Exponential decay of staggered moment

  15. Behavior of the relaxation time with anisotropy See also: Sengupta, Powell & Sachdev (2004) • Moment always decays to zero. Even for high easy axis anisotropy • Minimum of relaxation time at the QCP. Opposite of classical critical slowing. • Divergent relaxation time at the solvable XX point.

  16. Ramsey interference in 1d condensates Many-body decoherence

  17. Interaction induced collapse of Ramsey fringes Two component BEC. Single mode approximation Ramsey fringe visibility time Experiments in 1d tubes: A. Widera et al. PRL 100:140401 (2008)

  18. Spin echo. Time reversal experiments Single mode approximation The Hamiltonian can be reversed by changing a12 Predicts perfect spin echo

  19. Spin echo. Time reversal experiments A. Widera et al., PRL 2008 Experiments done in array of tubes. Strong fluctuations in 1d systems. Single mode approximation does not apply. Need to analyze the full model No revival?

  20. Interaction induced collapse of Ramsey fringes.Multimode analysis Low energy effective theory: Luttinger liquid approach Luttinger model Changing the sign of the interaction reverses the interaction part of the Hamiltonian but not the kinetic energy Time dependent harmonic oscillators can be analyzed exactly

  21. Interaction induced collapse of Ramsey fringesin one dimensional systems Only q=0 mode shows complete spin echo Finite q modes continue decay The net visibility is a result of competition between q=0 and other modes Decoherence due to many-body dynamics of low dimensional systems Fundamental limit on Ramsey interferometry How to distinquish decoherence due to many-body dynamics?

  22. Interaction induced collapse of Ramsey fringes Single mode analysis Kitagawa, Ueda, PRA 47:5138 (1993) Multimode analysis evolution of spin distribution functions T. Kitagawa, S. Pielawa, A. Imambekov, et al.

  23. Magnetism of ultracold atoms: Quantum many-body dynamics Superexchange and spin dynamics in optical lattices - superexchange interactions in Mott state - observation of superexchange in double well systems - spin dynamics of 1d chain Ramsey interference experiments in one dimensional systems - many-body decoherence

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