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arXiv:1403.7081 · Physical Review A

Observing properties of an interacting homogeneous Bose-Einstein condensate: Heisenberg-limited momentum spread, interaction energy, and free-expansion dynamics

Igor Gotlibovych, Tobias F. Schmidutz, Alexander L. Gaunt, Nir Navon, Robert P. Smith, Zoran Hadzibabic

Published Jun 30, 2014• 58 citations
arXivHTMLPDF

Abstract

We study the properties of an atomic Bose--Einstein condensate produced in an optical-box potential, using high-resolution Bragg spectroscopy. For a range of box sizes, up to $70\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}$m, we directly observe Heisenberg-limited momentum uncertainty of the condensed atoms. We measure the condensate interaction energy with a precision of ${k}_{\mathrm{B}}\ifmmode\times\else\texttimes\fi{}100$ pK and study, both experimentally and numerically, the dynamics of its free expansion upon release from the box potential. All our measurements are in good agreement with theoretical expectations for a perfectly homogeneous condensate of spatial extent equal to the size of the box, which also establishes the uniformity of our optical-box system on a sub-nK energy scale.

DOI
10.1103/physreva.89.061604

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This thesis describes studies of out-of-equilibrium dynamics in an interacting homogeneous Bose gas. We use the versatile platform of an ultracold gas of 39^{39}39K, prepared in an optical box trap. The experiment features both tuneable interaction strengths and a homogeneous atomic density. We examine first a weakly interacting near-equilibrium system, followed by far-from-equilibrium dynamics under moderate interactions, and finally combine strong interactions with highly non-equilibrium dynamics in studies of the unitary Bose gas. We start with a theoretical study of the effects of three-body recombination on the temperature of a weakly interacting, partially condensed gas. Contrary to the expectation of heating, we find that for appropriate values of the condensed fraction and gas parameter, the system temperature is expected to decrease. Not only do we predict lower temperatures, however, but also for the condensate fraction to grow. We then present experiments in which we engineer a far-from-equilibrium momentum distribution, and study the dynamics as the gas relaxes. As the distribution evolves, we observe bidirectional dynamic scaling, with a flow of particles to lower momenta while energy is transported to higher ones. These flows are characterised by spatiotemporal scaling exponents, which we find do not vary appreciably over a range of moderate interaction strengths. Finally, we look to the unitary Bose gas, quenching clouds into the strongly interacting regime. This regime offers insight into universal behaviour that depends only on the interparticle spacing, as well as being an avenue for the study of Efimov physics. However, few things come for free; strongly interacting Bose systems are plagued by high atom-loss and heating rates. We study atom-loss rates and the dynamics of correlations in our gases, isolate the coherent effects from the dissipative ones, and identify a quasi-equilibrium state that features a non-zero condensate fraction.
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