150 research outputs found
Detecting multiparticle entanglement of Dicke states
Recent experiments demonstrate the production of many thousands of neutral
atoms entangled in their spin degrees of freedom. We present a criterion for
estimating the amount of entanglement based on a measurement of the global
spin. It outperforms previous criteria and applies to a wide class of entangled
states, including Dicke states. Experimentally, we produce a Dicke-like state
using spin dynamics in a Bose-Einstein condensate. Our criterion proves that it
contains at least genuine 28-particle entanglement. We infer a generalized
squeezing parameter of -11.4(5) dB.Comment: 5 pages, 4 figure
Finite-temperature behavior of the Bose polaron
We consider a mobile impurity immersed in a Bose gas at finite temperature.
Using perturbation theory valid for weak coupling between the impurity and the
bosons, we derive analytical results for the energy and damping of the impurity
for low and high temperatures, as well as for temperatures close to the
critical temperature for Bose-Einstein condensation. These results show
that the properties of the impurity vary strongly with temperature. In
particular, the energy exhibits a non-monotonic behavior close to , and
the damping rises sharply close to . We argue that this behaviour is
generic for impurities immersed in an environment undergoing a phase transition
that breaks a continuous symmetry. Finally, we discuss how these effects can be
detected experimentally.Comment: 10 pages and 6 figure
Spontaneous symmetry breaking in spinor Bose-Einstein condensates
We present an analytical model for the theoretical analysis of spin dynamics
and spontaneous symmetry breaking in a spinor Bose-Einstein condensate (BEC).
This allows for an excellent intuitive understanding of the processes and
provides good quantitative agreement with experimental results in Phys. Rev.
Lett. 105, 135302 (2010). It is shown that the dynamics of a spinor BEC
initially prepared in an unstable Zeeman state mF=0 (|0>) can be understood by
approximating the effective trapping potential for the state |+-1> with a
cylindrical box potential. The resonances in the creation efficiency of these
atom pairs can be traced back to excitation modes of this confinement. The
understanding of these excitation modes allows for a detailed characterization
of the symmetry breaking mechanism, showing how a twofold spontaneous breaking
of spatial and spin symmetry can occur. In addition a detailed account of the
experimental methods for the preparation and analysis of spinor quantum gases
is given.Comment: 12 pages, 14 figure
Preparation of ultracold atom clouds at the shot noise level
We prepare number stabilized ultracold clouds through the real-time analysis
of non-destructive images and the application of feedback. In our experiments,
the atom number is determined by high precision Faraday imaging
with uncertainty below the shot noise level, i.e., . Based on this measurement, feedback is applied to reduce the atom
number to a user-defined target, whereupon a second imaging series probes the
number stabilized cloud. By this method, we show that the atom number in
ultracold clouds can be prepared below the shot noise level.Comment: Main text: 4 Figures, 4 pages. Supplemental Information: 4 figures, 5
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