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Vienna, Austria

Sakmann K.,Stanford University | Sakmann K.,Atominstitut Vienna | Kasevich M.,Stanford University
Nature Physics | Year: 2016

Single experimental shots of ultracold quantum gases sample the many-particle probability distribution. In a few cases such single shots could be successfully simulated from a given many-body wavefunction, but for realistic time-dependent many-body dynamics this has been difficult to achieve. Here, we show how single shots can be simulated from numerical solutions of the time-dependent many-body Schrödinger equation. Using this approach, we provide first-principle explanations for fluctuations in the collision of attractive Bose-Einstein condensates (BECs), for the appearance of randomly fluctuating vortices and for the centre-of-mass fluctuations of attractive BECs in a harmonic trap. We also show how such simulations provide full counting distributions and correlation functions of any order. Such calculations have not been previously possible and our method is broadly applicable to many-body systems whose phenomenology is driven by information beyond what is typically available in low-order correlation functions. © 2016 Macmillan Publishers Limited. Source

Mazets I.E.,Atominstitut Vienna | Mazets I.E.,RAS Ioffe Physical - Technical Institute
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

Expansion of a degenerate Bose gas released from a pancakelike trap is numerically simulated under the assumption of separation of the motion in the plane of the loose initial trapping and the motion in the direction of the initial tight trapping. The initial conditions for the phase fluctuations are generated using the extension to the two-dimensional case of the description of the phase noise by the Ornstein-Uhlenbeck stochastic process. The numerical simulations, taking into account both the finite size of the two-dimensional system and the atomic interactions, which cannot be neglected on the early stage of expansion, did not reproduce the scaling law for the peaks in the density fluctuation spectra experimentally observed by Choi, Seo, Kwon, and Shin. The latter experimental results may thus require an explanation beyond our current assumptions. © 2012 American Physical Society. Source

Mazets I.E.,Atominstitut Vienna | Mazets I.E.,RAS Ioffe Physical - Technical Institute | Schmiedmayer J.,Atominstitut Vienna
New Journal of Physics | Year: 2010

We study the collisional processes that can lead to thermalization in one-dimensional (1D) systems. For two-body collisions, excitations of transverse modes are the prerequisite for energy exchange and thermalization. At very low temperatures, excitations of transverse modes are exponentially suppressed, thermalization by two-body collisions stops and the system should become integrable. In quantum mechanics, virtual excitations of higher radial modes are possible. These virtually excited radial modes give rise to effective three-body velocity-changing collisions, which lead to thermalization. We show that these three-body elastic interactions are suppressed by pairwise quantum correlations when approaching the strongly correlated regime. If the relative momentum k is small compared with the two-body coupling constant c, the three-particle scattering state is suppressed by a factor of (k/c)12, which is proportional to γ-12, that is, to the square of the three-body correlation function at zero distance in the limit of the Lieb-Liniger parameter γ ≫ 1. This demonstrates that in ID quantum systems, it is not the freeze-out of two-body collisions but the strong quantum correlations that ensure absence of thermalization on experimentally relevant time scales. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Source

Wuttke C.,Atominstitut Vienna | Rauschenbeutel A.,Atominstitut Vienna
Physical Review Letters | Year: 2013

Modeling and investigating the thermalization of microscopic objects with arbitrary shape from first principles is of fundamental interest and may lead to technical applications. Here, we study, over a large temperature range, the thermalization dynamics due to far-field heat radiation of an individual, deterministically produced silica fiber with a predetermined shape and a diameter smaller than the thermal wavelength. The temperature change of the subwavelength-diameter fiber is determined through a measurement of its optical path length in conjunction with an ab initio thermodynamic model of the fiber structure. Our results show excellent agreement with a theoretical model that considers heat radiation as a volumetric effect and takes the emitter shape and size relative to the emission wavelength into account. © 2013 American Physical Society. Source

Reitz D.,Atominstitut Vienna | Rauschenbeutel A.,Atominstitut Vienna
Optics Communications | Year: 2012

A double-helix optical trapping potential for cold atoms can be straightforwardly created inside the evanescent field of an optical nanofiber. It suffices to send three circularly polarized light fields through the nanofiber; two counterpropagating and far red-detuned with respect to the atomic transition and the third far blue-detuned. Assuming realistic experimental parameters, the transverse confinement of the resulting potential allows one to reach the one-dimensional regime with cesium atoms for temperatures of several μK. Moreover, by locally varying the nanofiber diameter, the radius and pitch of the double-helix can be modulated, thereby opening a realm of applications in cold-atom physics. © 2012 Elsevier B.V. Source

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