Amplifying single impurities immersed in a gas of ultra cold atoms

We present a method for amplifying a single or scattered impurities immersed in a background gas of ultra cold atoms so that they can be optically imaged and spatially resolved. Our approach relies on a Raman transfer between two stable atomic hyperfine states that is conditioned on the presence of an impurity atom. The amplification is based on the strong interaction among atoms excited to Rydberg states. We perform a detailed analytical study of the performance of the proposed scheme with particular emphasis on the influence of many-body effects.Comment: 5 pages, 4 figure

Breakdown of integrability in a quasi-one-dimensional ultracold bosonic gas

We demonstrate that virtual excitations of higher radial modes in an atomic Bose gas in a tightly confining waveguide result in effective three-body collisions that violate integrability in this quasi-one-dimensional quantum system and give rise to thermalization. The estimated thermalization rates are consistent with recent experimental results in quasi-1D dynamics of ultracold atoms.Comment: 4 pages, 3 figures, revtex

Proclaiming a prophecy empty of substance?: A pragmatist reconsideration of global governance

In 1995, the UN Commission on Global Governance published their “Our Global Neighbourhood” report and the academic journal “Global Governance: A Review of Multilateralism and International Organizations” was launched. Both events in retrospect play a significant role in the emergence of global governance thinking and practice in world politics. Despite inherent ambiguities, this idea since then gained massive traction and became both a modality and a heuristic of world politics. Advancing a pragmatist framework, we unpack global governance in terms of the beliefs which underline and guide it. These beliefs are important since they, as rules for action, define the scope of global governance as a theoretical and a political concept. Reconstructing these beliefs directly from the 1995 report, the article highlights the inherent conflations of normative and analytical commitments indicative of global governance. As a projection surface of all kinds, we believe such a reconsideration of global governance is important to (a) reveal the baselines of its thinking and practice, (b) indicate how its normative and analytical ambitions overlap and conflate, and (c) contribute to a more reflective discussion on the idea which explicitly considers its inherent normativity. At the same time, we hope to show the value of a pragmatist framework on beliefs for the study of world politics

Disorder Potentials near Lithographically Fabricated Atom Chips

We show that previously observed large disorder potentials in magnetic microtraps for neutral atoms are reduced by about two orders of magnitude when using atom chips with lithographically fabricated high quality gold layers. Using one dimensional Bose-Einstein condensates, we probe the remaining magnetic field variations at surface distances down to a few microns. Measurements on a 100 um wide wire imply that residual variations of the current flow result from local properties of the wire.Comment: submitted on September 24th, 200

Ultracold atoms in radio-frequency-dressed potentials beyond the rotating wave approximation

We study dressed Bose-Einstein condensates in an atom chip radio-frequency trap. We show that in this system sufficiently strong dressing can be achieved to cause the widely used rotating wave approximation (RWA) to break down. We present a full calculation of the atom - field coupling which shows that the non-RWA contributions quantitatively alter the shape of the emerging dressed adiabatic potentials. The non-RWA contributions furthermore lead to additional allowed transitions between dressed levels. We use RF spectroscopy of Bose-Einstein condensates trapped in the dressed state potentials to directly observe the transition from the RWA to the beyond-RWA regime.Comment: 6 pages, 4 figure

Electromagnetically induced transparency of ultralong-range Rydberg molecules

We study the impact of Rydberg molecule formation on the storage and retrieval of Rydberg polaritons in an ultracold atomic medium. We observe coherent revivals appearing in the retrieval efficiency of stored photons that originate from simultaneous excitation of Rydberg atoms and Rydberg molecules in the system with subsequent interference between the possible storage paths. We show that over a large range of principal quantum numbers the observed results can be described by a two-state model including only the atomic Rydberg state and the Rydberg dimer molecule state. At higher principal quantum numbers the influence of polyatomic molecules becomes relevant and the dynamics of the system undergoes a transition from coherent evolution of a few-state system to an effective dephasing into a continuum of molecular states.Comment: Submitted to PR