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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.

Volz J.,Atominstitut Vienna | Scheucher M.,Atominstitut Vienna | Junge C.,Atominstitut Vienna | Rauschenbeutel A.,Atominstitut Vienna
Nature Photonics | Year: 2014

Realizing a strong interaction between individual photons is an important objective of research in quantum science and technology. It requires an optical medium in which light experiences a phase shift that depends nonlinearly on the photon number. Once the additional two-photon phase shift reaches Ï €, such an ultra-strong nonlinearity could enable the implementation of high-fidelity quantum logic operations. However, the nonlinear response of standard optical media is orders of magnitude too weak. Here, we demonstrate a fibre-based nonlinearity that realizes an additional two-photon phase shift close to the ideal value of Ï €. We employ a whispering-gallery-mode resonator, interfaced by an optical nanofibre, where the presence of a single rubidium atom in the resonator mode results in a strongly nonlinear response. We show that this results in entanglement of initially uncorrelated incident photons. This demonstration of a fibre-integrated, ultra-strong nonlinearity is a decisive step towards photon-based scalable quantum logics. © 2014 Macmillan Publishers Limited. All rights reserved.

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.

Langen T.,Atominstitut Vienna | Geiger R.,Atominstitut Vienna | Schmiedmayer J.,Atominstitut Vienna
Annual Review of Condensed Matter Physics | Year: 2015

The relaxation of isolated quantum many-body systems is a major unsolved problem connecting statistical and quantum physics. Studying such relaxation processes remains a challenge despite considerable efforts. Experimentally, it requires the creation and manipulation of well-controlled and truly isolated quantum systems. In this context, ultracold neutral atoms provide unique opportunities to understand nonequilibrium phenomena because of the large set of available methods to isolate, manipulate, and probe these systems. Here, we give an overview of the rapid experimental progress that has been made in the field over the past few years and highlight some of the questions that may be explored in the future. © 2015 by Annual Reviews.

Langen T.,Atominstitut Vienna | Geiger R.,Atominstitut Vienna | Kuhnert M.,Atominstitut Vienna | Rauer B.,Atominstitut Vienna | Schmiedmayer J.,Atominstitut Vienna
Nature Physics | Year: 2013

Understanding the dynamics of isolated quantum many-body systems is a central open problem at the intersection between statistical physics and quantum physics. Despite important theoretical effort, no generic framework exists yet to understand when and how an isolated quantum system relaxes to a steady state. Regarding the question of how, it has been conjectured that equilibration must occur on a local scale in systems where correlations between distant points can establish only at a finite speed. Here, we provide the first experimental observation of this local equilibration hypothesis. In our experiment, we quench a one-dimensional Bose gas by coherently splitting it into two parts. By monitoring the phase coherence between the two parts we observe that the thermal correlations of a prethermalized state emerge locally in their final form and propagate through the system in a light-cone-like evolution. Our results underline the close link between the propagation of correlations and relaxation processes in quantum many-body systems. © 2013 Macmillan Publishers Limited.

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.

Berrada T.,Atominstitut Vienna | Van Frank S.,Atominstitut Vienna | Bucker R.,Atominstitut Vienna | Schumm T.,Atominstitut Vienna | And 2 more authors.
Nature Communications | Year: 2013

Particle-wave duality enables the construction of interferometers for matter waves, which complement optical interferometers in precision measurement devices. This requires the development of atom-optics analogues to beam splitters, phase shifters and recombiners. Integrating these elements into a single device has been a long-standing goal. Here we demonstrate a full Mach-Zehnder sequence with trapped Bose-Einstein condensates confined on an atom chip. Particle interactions in our Bose-Einstein condensate matter waves lead to a nonlinearity, absent in photon optics. We exploit it to generate a non-classical state having reduced number fluctuations inside the interferometer. Making use of spatially separated wave packets, a controlled phase shift is applied and read out by a non-adiabatic matter-wave recombiner. We demonstrate coherence times a factor of three beyond what is expected for coherent states, highlighting the potential of entanglement as a resource for metrology. Our results pave the way for integrated quantum-enhanced matter-wave sensors. © 2013 Macmillan Publishers Limited. All rights reserved.

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.

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.

Kazakov G.A.,Atominstitut Vienna | Schumm T.,Atominstitut Vienna
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

It has been proposed to use magnetically trapped atomic ensembles to enhance the interrogation time in microwave clocks. To mitigate the perturbing effects of the magnetic trap, near-magic-field configurations are employed, where the involved clock transition becomes independent of the atom's potential energy to first order. Still, higher order effects are a dominating source for dephasing, limiting the performance of this approach. Here we propose a simple method to cancel the energy dependence to both first and second order, using weak radio-frequency dressing. We give values for dressing frequencies, amplitudes, and trapping fields for 87Rb atoms and investigate quantitatively the robustness of these second-order-magic conditions to variations of the system parameters. We conclude that radio-frequency dressing can suppress field-induced dephasing by at least one order of magnitude for typical experimental parameters. © 2015 American Physical Society.

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