89 research outputs found
Detection of Pair-Superfluidity for bosonic mixtures in optical lattices
We consider a mixture of two bosonic species with tunable interspecies
interaction in a periodic potential and discuss the advantages of low filling
factors on the detection of the pair-superfluid phase. We show how the
emergence of such a phase can be put dramatically into evidence by looking at
the interference pictures and density correlations after expansion and by
changing the interspecies interaction from attractive to repulsive.Comment: 4 pages, 4 figure
Bose-Einstein condensates in 1D optical lattices: compressibility, Bloch bands and elementary excitations
We discuss the Bloch-state solutions of the stationary Gross-Pitaevskii
equation and of the Bogoliubov equations for a Bose-Einstein condensate in the
presence of a one-dimensional optical lattice. The results for the
compressibility, effective mass and velocity of sound are analysed as a
function of the lattice depth and of the strength of the two-body interaction.
The band structure of the spectrum of elementary excitations is compared with
the one exhibited by the stationary solutions (``Bloch bands''). Moreover, the
numerical calculations are compared with the analytic predictions of the tight
binding approximation. We also discuss the role of quantum fluctuations and
show that the condensate exhibits 3D, 2D or 1D features depending on the
lattice depth and on the number of particles occupying each potential well. We
finally show how, using a local density approximation, our results can be
applied to study the behaviour of the gas in the presence of harmonic trapping.Comment: version published in EPJ
Photothermally-induced disordered patterns of corneal collagen revealed by SHG imaging
The loss of organization of the corneal collagen lattice induced by photothermal effects was analyzed by using second-harmonic generation (SHG) imaging. Porcine cornea samples were treated with low-power laser irradiation in order to get localized areas of tissue disorganization. The disorder induced within the irradiated area of corneal stroma was quantified by means of Discrete Fourier Transform, auto-correlation and entropy analyses of the SHG images. Polarization modulated SHG measurements allowed to probe the changes in the structural anisotropy of sub-micron hierarchical levels of the stromal collagen. Our results emphasize the great potential of the SHG imaging to detect subtle modifications in the collagen assembly. The proposed analytical methods may be used to track several genetic, pathologic, accidental or surgical-induced disorder states of biological tissues
Collective oscillations of a 1D trapped Bose gas
Starting from the hydrodynamic equations of superfluids, we calculate the
frequencies of the collective oscillations of a harmonically trapped Bose gas
for various 1D configurations. These include the mean field regime described by
Gross-Pitaevskii theory and the beyond mean field regime at small densities
described by Lieb-Liniger theory. The relevant combinations of the physical
parameters governing the transition between the different regimes are
discussed.Comment: 4 pages, 2 figure
NADH Distribution in Live Progenitor Stem Cells by Phasor-Fluorescence Lifetime Image Microscopy
AbstractNADH is a naturally fluorescent metabolite associated with cellular respiration. Exploiting the different fluorescence lifetime of free and bound NADH has the potential to quantify the relative amount of bound and free NADH, enhancing understanding of cellular processes including apoptosis, cancer pathology, and enzyme kinetics. We use the phasor- fluorescence lifetime image microscopy approach to spatially map NADH in both the free and bound forms of live undifferentiated and differentiated myoblast cells. The phasor approach graphically depicts the change in lifetime at a pixel level without the requirement for fitting the decay. Comparison of the spatial distribution of NADH in the nucleus of cells induced to differentiate through serum starvation and undifferentiated cells show differing distributions of bound and free NADH. Undifferentiated cells displayed a short lifetime indicative of free NADH in the nucleus and a longer lifetime attributed to the presence of bound NADH outside of the nucleus. Differentiating cells displayed redistribution of free NADH with decreased relative concentration of free NADH within the nucleus whereas the majority of NADH was found in the cytoplasm
Collective decoherence of cold atoms coupled to a Bose-Einstein condensate
We examine the time evolution of cold atoms (impurities) interacting with an
environment consisting of a degenerate bosonic quantum gas. The impurity atoms
differ from the environment atoms, being of a different species. This allows
one to superimpose two independent trapping potentials, each being effective
only on one atomic kind, while transparent to the other. When the environment
is homogeneous and the impurities are confined in a potential consisting of a
set of double wells, the system can be described in terms of an effective
spin-boson model, where the occupation of the left or right well of each site
represents the two (pseudo)-spin states. The irreversible dynamics of such
system is here studied exactly, i.e., not in terms of a Markovian master
equation. The dynamics of one and two impurities is remarkably different in
respect of the standard decoherence of the spin - boson system. In particular
we show: i) the appearance of coherence oscillations, i) the presence of super
and sub decoherent states which differ from the standard ones of the spin boson
model, and iii) the persistence of coherence in the system at long times. We
show that this behaviour is due to the fact that the pseudospins have an
internal spatial structure. We argue that collective decoherence also prompts
information about the correlation length of the environment. In a one
dimensional configuration one can change even stronger the qualitative
behaviour of the dephasing just by tuning the interaction of the bath.Comment: 18 pages, 6 figures, two references adde
Coupling ultracold atoms to mechanical oscillators
In this article we discuss and compare different ways to engineer an
interface between ultracold atoms and micro- and nanomechanical oscillators. We
start by analyzing a direct mechanical coupling of a single atom or ion to a
mechanical oscillator and show that the very different masses of the two
systems place a limit on the achievable coupling constant in this scheme. We
then discuss several promising strategies for enhancing the coupling:
collective enhancement by using a large number of atoms in an optical lattice
in free space, coupling schemes based on high-finesse optical cavities, and
coupling to atomic internal states. Throughout the manuscript we discuss both
theoretical proposals and first experimental implementations.Comment: 19 pages, 9 figure
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