10,658 research outputs found
Bragg spectroscopy of trapped one dimensional strongly interacting bosons in optical lattices: Probing the cake-structure
We study Bragg spectroscopy of strongly interacting one dimensional bosons
loaded in an optical lattice plus an additional parabolic potential. We
calculate the dynamic structure factor by using Monte Carlo simulations for the
Bose-Hubbard Hamiltonian, exact diagonalizations and the results of a recently
introduced effective fermionization (EF) model. We find that, due to the
system's inhomogeneity, the excitation spectrum exhibits a multi-branched
structure, whose origin is related to the presence of superfluid regions with
different densities in the atomic distribution. We thus suggest that Bragg
spectroscopy in the linear regime can be used as an experimental tool to unveil
the shell structure of alternating Mott insulator and superfluid phases
characteristic of trapped bosons.Comment: 7 pages, 4 figure
Macroscopic superposition states in rotating ring lattices
We investigate the effects of rotation on one-dimensional ultracold bosons
confined to optical ring lattices. First, we show that there exists a critical
rotation frequency at which the ground state of a weakly-interacting and
integer-filled atomic gas is fragmented into a macroscopic superposition state
with different circulation. Second, we point out several advantages of using
slightly non-uniform ring lattices. Finally, we demonstrate that different
quasi-momentum states can be distinguished in time-of-flight absorption imaging
and propose to probe correlations via the many-body oscillations induced by a
sudden change in the rotation frequency.Comment: 8 pages, 4 figures; PQE-2008 conference proceedings; minor
correction
On the Outage Probability of the Full-Duplex Interference-Limited Relay Channel
In this paper, we study the performance, in terms of the asymptotic error
probability, of a user which communicates with a destination with the aid of a
full-duplex in-band relay. We consider that the network is
interference-limited, and interfering users are distributed as a Poisson point
process. In this case, the asymptotic error probability is upper bounded by the
outage probability (OP). We investigate the outage behavior for well-known
cooperative schemes, namely, decode-and-forward (DF) and compress-and-forward
(CF) considering fading and path loss. For DF we determine the exact OP and
develop upper bounds which are tight in typical operating conditions. Also, we
find the correlation coefficient between source and relay signals which
minimizes the OP when the density of interferers is small. For CF, the
achievable rates are determined by the spatial correlation of the
interferences, and a straightforward analysis isn't possible. To handle this
issue, we show the rate with correlated noises is at most one bit worse than
with uncorrelated noises, and thus find an upper bound on the performance of
CF. These results are useful to evaluate the performance and to optimize
relaying schemes in the context of full-duplex wireless networks.Comment: 30 pages, 4 figures. Final version. To appear in IEEE JSAC Special
Issue on Full-duplex Wireless Communications and Networks, 201
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