6,637 research outputs found
Short note on the excitonic Mott phase
An exciton gas on a lattice is analyzed in terms of a convergent hopping
expansion. For a given chemical potential our calculation provides a sufficient
condition for the hopping rate to obtain an exponential decay of the exciton
correlation function. This result indicates the existence of a Mott phase in
which strong fluctuations destroy the long range correlations in the exciton
gas at any temperature, either by thermal or by quantum fluctuations.Comment: 5 pages, 1 figur
On the Riemann Tensor in Double Field Theory
Double field theory provides T-duality covariant generalized tensors that are
natural extensions of the scalar and Ricci curvatures of Riemannian geometry.
We search for a similar extension of the Riemann curvature tensor by developing
a geometry based on the generalized metric and the dilaton. We find a duality
covariant Riemann tensor whose contractions give the Ricci and scalar
curvatures, but that is not fully determined in terms of the physical fields.
This suggests that \alpha' corrections to the effective action require \alpha'
corrections to T-duality transformations and/or generalized diffeomorphisms.
Further evidence to this effect is found by an additional computation that
shows that there is no T-duality invariant four-derivative object built from
the generalized metric and the dilaton that reduces to the square of the
Riemann tensor.Comment: 36 pages, v2: minor changes, ref. added, v3: appendix on frame
formalism added, version to appear in JHE
Atomic population distribution in the output ports of cold-atom interferometers with optical splitting and recombination
Cold-atom interferometers with optical splitting and recombination use
off-resonant laser beams to split a cloud of Bose-Einstein condensate (BEC)
into two clouds that travel along different paths and are then recombined again
using optical beams. After the recombination, the BEC in general populates both
the cloud at rest and the moving clouds. Measuring relative number of atoms in
each of these clouds yields information about the relative phase shift
accumulated by the atoms in the two moving clouds during the interferometric
cycle. We derive the expression for the probability of finding any given number
of atoms in each of the clouds, discuss features of the probability density
distribution, analyze its dependence on the relative accumulated phase shift as
a function of the strength of the interatomic interactions, and compare our
results with experiment.Comment: 25 pages, 7 figure
Spectrum of light scattering from an extended atomic wave packet
The spectrum of the light scattered from an extended atomic wave packet is
calculated. For a wave packet consisting of two spatially separated peaks
moving on parallel trajectories, the spectrum contains Ramsey-like fringes that
are sensitive to the phase difference between the two components of the wave
packet. Using this technique, one can establish the mutual coherence of the two
components of the wave packet without recombining them.Comment: 4 page
A Double Sigma Model for Double Field Theory
We define a sigma model with doubled target space and calculate its
background field equations. These coincide with generalised metric equation of
motion of double field theory, thus the double field theory is the effective
field theory for the sigma model.Comment: 26 pages, v1: 37 pages, v2: references added, v3: updated to match
published version - background and detail of calculations substantially
condensed, motivation expanded, refs added, results unchange
Sensitive linear response of an electron-hole superfluid in a periodic potential
We consider excitons in a two-dimensional periodic potential and study the
linear response of the excitonic superfluid to an electromagnetic wave at low
and high densities. It turns out that the static structure factor for small
wavevectors is very sensitive to a change of density and temperature. It is a
consequence of the fact that thermal fluctuations play a crucial role at small
wavevectors, since exchanging the order of the two limits, zero temperature and
vanishing wavevector, leads to different results for the structure factor. This
effect could be used for high accuracy measurements in the superfluid exciton
phase, which might be realized by a gated electron-hole gas. The transition of
the exciton system from the superfluid state to a non-superfluid state and its
manifestation by light scattering are discussed.Comment: 9 pages, 5 figure
On mechanisms that enforce complementarity
In a recent publication Luis and Sanchez-Soto arrive at the conclusion that
complementarity is universally enforced by random classical phase kicks. We
disagree. One could just as well argue that quantum entanglement is the
universal mechanism. Both claims of universality are unjustified, however.Comment: 4 page
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