19,031 research outputs found
Characteristics of Bose-Einstein condensation in an optical lattice
We discuss several possible experimental signatures of the Bose-Einstein
condensation (BEC) transition for an ultracold Bose gas in an inhomogeneous
optical lattice. Based on the commonly used time-of-flight imaging technique,
we show that the momentum-space density profile in the first Brillouin zone,
supplemented by the visibility of interference patterns, provides valuable
information about the system. In particular, by crossing the BEC transition
temperature, the appearance of a clear bimodal structure sets a qualitative and
universal signature of this phase transition. Furthermore, the momentum
distribution can also be applied to extract the condensate fraction, which may
serve as a promising thermometer in such a system.Comment: 12 pages, 13 figures; Revised version with new figures; Phys. Rev. A
77, 043626 (2008
Signal of Bose condensation in an optical lattice at finite temperature
We discuss the experimental signal for the Bose condensation of cold atoms in
an optical lattice at finite temperature. Instead of using the visibility of
the interference pattern via the time-of-flight imaging, we show that the
momentum space density profile in the first Brillouin zone, in particular its
bimodal distribution, provides an unambiguous signal for the Bose condensation.
We confirm this point with detailed calculation of the change in the atomic
momentum distribution across the condensation phase transition, taking into
account both the global trapping potential and the atomic interaction effects.Comment: 4 pages, 2 figures, replaced with the published versio
A new Bloch period for interacting cold atoms in 1D optical lattices
The paper studies Bloch oscillations of ultracold atoms in optical lattice in
the presence of atom-atom interaction. A new, interaction-induced Bloch period
is identified. The analytical results are corroborated by realistic numerical
calculations.Comment: revtex4, 4 pages, 4 figures, gzipped tar fil
Possibility of Coherent Phenomena like Bloch Oscillations with Single Photons via W-States
We examine the behavior of single photons at multiport devices and inquire if
coherent effects are possible. In particular we study how single photons need
to be manipulated in order to study coherent phenomena. We show that single
photons need to be produced in W states which lead to vanishing mean amplitude
but nonzero correlations between the inputs at different ports. Such
correlations restore coherent effects with single photons. As a specific
example we demonstrate Bloch oscillations with single photons and thus provide
strict analog of Bloch oscillation of electrons.Comment: 5 pages, 7 figure
Individual complex Dirac eigenvalue distributions from random matrix theory and comparison to quenched lattice QCD with a quark chemical potential
We analyze how individual eigenvalues of the QCD Dirac operator at nonzero
quark chemical potential are distributed in the complex plane. Exact and
approximate analytical results for both quenched and unquenched distributions
are derived from non-Hermitian random matrix theory. When comparing these to
quenched lattice QCD spectra close to the origin, excellent agreement is found
for zero and nonzero topology at several values of the quark chemical
potential. Our analytical results are also applicable to other physical systems
in the same symmetry class.Comment: 4 pages, 4 figures, minor changes, as published in Phys. Rev. Let
Isentropic Curves at Magnetic Phase Transitions
Experiments on cold atom systems in which a lattice potential is ramped up on
a confined cloud have raised intriguing questions about how the temperature
varies along isentropic curves, and how these curves intersect features in the
phase diagram. In this paper, we study the isentropic curves of two models of
magnetic phase transitions- the classical Blume-Capel Model (BCM) and the Fermi
Hubbard Model (FHM). Both Mean Field Theory (MFT) and Monte Carlo (MC) methods
are used. The isentropic curves of the BCM generally run parallel to the phase
boundary in the Ising regime of low vacancy density, but intersect the phase
boundary when the magnetic transition is mainly driven by a proliferation of
vacancies. Adiabatic heating occurs in moving away from the phase boundary. The
isentropes of the half-filled FHM have a relatively simple structure, running
parallel to the temperature axis in the paramagnetic phase, and then curving
upwards as the antiferromagnetic transition occurs. However, in the doped case,
where two magnetic phase boundaries are crossed, the isentrope topology is
considerably more complex
Alternative structures and bi-Hamiltonian systems on a Hilbert space
We discuss transformations generated by dynamical quantum systems which are
bi-unitary, i.e. unitary with respect to a pair of Hermitian structures on an
infinite-dimensional complex Hilbert space. We introduce the notion of
Hermitian structures in generic relative position. We provide few necessary and
sufficient conditions for two Hermitian structures to be in generic relative
position to better illustrate the relevance of this notion. The group of
bi-unitary transformations is considered in both the generic and non-generic
case. Finally, we generalize the analysis to real Hilbert spaces and extend to
infinite dimensions results already available in the framework of
finite-dimensional linear bi-Hamiltonian systems.Comment: 11 page
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