T. Kitagawa (Harvard), S. Pielawa (Harvard), D. Pekker (Harvard), R. Sensarma (Harvard/JQI), V. Gritsev (Fribourg), M. Lukin (Harvard), Lode Pollet (Harvard)

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T. Kitagawa (Harvard), S. Pielawa (Harvard), D. Pekker (Harvard), R. Sensarma (Harvard/JQI), V. Gritsev (Fribourg), M. Lukin (Harvard), Lode Pollet (Harvard) Eugene Demler Harvard University Collaboration with experimental groups of T. Esslinger, I. Bloch, J. Schmiedmayer Probing many-body systems of ultracold atoms $$ NSF, MURI, DARPA, AFOSR Harvard-MIT

Outline Lattice modulation experiments with fermions Ramsey interference experiments in 1d Also yesterday’s talks by Henning Moritz and Andreas Ruegg

Lattice modulation experiments with fermions in optical lattice. Probing the Mott state of fermions Expts: Joerdens et al., Nature (2008) Greif, Tarruell, Strohmaier, Moritz, Esslinger et al. Theory: Kollath et al., PRA (2006) Huber, Ruegg, PRA (2009) Sensarma et al. PRL 2009 Pollet, Pekker, Demler, unpublished Yesterday’s talks by Henning Moritz and Andreas Ruegg

Lattice modulation experiments Probing dynamics of the Hubbard model Measure number of doubly occupied sites Main effect of shaking: modulation of tunneling Modulate lattice potential Doubly occupied sites created when frequency w matches Hubbard U

Lattice modulation experiments Probing dynamics of the Hubbard model R. Joerdens et al., Nature 455:204 (2008)

Mott state Regime of strong interactions U>>t. Mott gap for the charge forms at Antiferromagnetic ordering at “High” temperature regime All spin configurations are equally likely. Can neglect spin dynamics.

Doublon production rate depends on propagation of doublons and holes Retraceable Path Approximation Brinkmann & Rice, 1970 Spectral Fn. of single holeDoublon Production Rate Experimental data courtesy of D. Greif preliminary data

A d(h) is the spectral function of a single doublon (holon) Sum Rule : Lattice modulation experiments. Sum rule Simple model to include temperature dependence and trap: multiply production rate by the average fraction of nearest neighbors with opposite spins T-independent ? preliminary data courtesy of D. Greif

Ramsey Interference in one dimensional systems Using quantum noise to study many-body dynamics

One dimensional systems in condensed matter Non-perturbative effects of interactions: Absense of long range order Electron fractionalization Emphasis on equilibrium properties and linear response 1d organics carbon nanotubes GaAs/AlGaAs Heterostructures

1d systems of ultracold atoms: analysis of nonequilibrium dynamics Time evolution of coherence in split condensates S. Hofferberth et al., Nature (2007) 1D Ramsey Interferometry (Widera, et.al PRL 2008)

Introduction: Ramsey Interference

Working with N atoms improves the precision by. Ramsey interference t 0 1 Atomic clocks and Ramsey interference:

Ramsey Interference with BEC Spin squeezing: possible application in quantum enhanced metrology Sorensen, Moller, Cirac, Zoller, Lewensstein, … Gaussian distribution of S z Single mode approximation

1d systems in microchips Treutlein et.al, PRL 2004 Two component BEC in microchip Ramsey Interference with 1d BEC 1d systems in optical lattices Ramsey interference in 1d tubes: A.Widera et al., B. PRL 100: (2008)

Ramsey Interference in 1d: a probe of many-body dynamics

Ramsey interference in 1d condensates A. Widera, et al, PRL 2008 Only partial revival after spin echo! Spin echo experiments Expect full revival of fringes

Spin echo experiments in 1d tubes Single mode approximation does not apply. Need to analyze the full model

Low energy effective Hamiltonian for spin dynamics Bosonization Tomonaga-Luttinger Hamiltonian 19

Ramsey interference: Initial State After p /2 pulse, spins point in x direction Small uncertainty in Initial state: squeezed state in f s W k determined from Short distance cut-off at spin healing length related argument in Bistrizer, Altman, PNAS (2008)

Ramsey interference in 1d Time evolution Technical noise could also lead to the absence of echo Need “smoking gun” signatures of many-body decoherece Luttinger liquid provides good agreement with experiments. A. Widera et al., PRL Theory: V. Gritsev

Distribution functions of Ramsey amplitude

Distribution Probing spin dynamics through distribution functions Distribution function contains information about higher order correlations Joint distribution function can also be obtained

Interference of independent 1d condensates S. Hofferberth, I. Lesanovsky, T. Schumm, J. Schmiedmayer, A. Imambekov, V. Gritsev, E. Demler, Nature Physics (2008) Higher order correlation functions probed by noise in interference

Joint distribution functions Short segments |S|^2 does not change but Sx decays Long segments both Sx and |S|^2 decay

Two regimes of spin dynamics Modes with λ>l leads to the decay of Sx but not |S| Modes with λ<l leads to the decay of both Sx and |S|

Analytic solution for the distribution function

Summary Suggested unique signatures of the multimode decoherence of Ramsey fringes in 1d Ramsey interferometer combined with study of distribution function is a useful tool to probe many-body dynamics Joint distribution functions provide simple visualization of complicated many-body dynamics