576 research outputs found
Photon molecules in atomic gases trapped near photonic crystal waveguides
Realizing systems that support robust, controlled interactions between
individual photons is an exciting frontier of nonlinear optics. To this end,
one approach that has emerged recently is to leverage atomic interactions to
create strong and spatially non-local interactions between photons. In
particular, effective interactions have been successfully created via
interactions between atoms excited to Rydberg levels. Here, we investigate an
alternative approach, in which atomic interactions arise via their common
coupling to photonic crystal waveguides. This technique takes advantage of the
ability to separately tailor the strength and range of interactions via the
dispersion engineering of the structure itself, which can lead to qualitatively
new types of phenomena. As an example, we discuss the formation of correlated
transparency windows, in which photonic states of a certain number and shape
selectively propagate through the system. Through this technique, we show in
particular that one can create molecular-like potentials that lead to molecular
bound states of photon pairs
Adiabatic quantum dynamics of the Lipkin-Meshkov-Glick model
The adiabatic quantum evolution of the Lipkin-Meshkov-Glick (LMG) model
across its quantum critical point is studied. The dynamics is realized by
linearly switching the transverse field from an initial large value towards
zero and considering different transition rates. We concentrate our attention
on the residual energy after the quench in order to estimate the level of
diabaticity of the evolution. We discuss a Landau-Zener approximation of the
finite size LMG model, that is successful in reproducing the behavior of the
residual energy as function of the transition rate in the most part of the
regimes considered. We also support our description through the analysis of the
entanglement entropy of the evolved state. The system proposed is a paradigm of
infinite-range interaction or high-dimensional models.Comment: 8 pages, 7 figures. (v2) minor revisions, published versio
Adiabatic quantum dynamics of a random Ising chain across its quantum critical point
We present here our study of the adiabatic quantum dynamics of a random Ising
chain across its quantum critical point. The model investigated is an Ising
chain in a transverse field with disorder present both in the exchange coupling
and in the transverse field. The transverse field term is proportional to a
function which, as in the Kibble-Zurek mechanism, is linearly
reduced to zero in time with a rate , , starting
at from the quantum disordered phase () and ending
at in the classical ferromagnetic phase (). We first analyze
the distribution of the gaps -- occurring at the critical point --
which are relevant for breaking the adiabaticity of the dynamics. We then
present extensive numerical simulations for the residual energy
and density of defects at the end of the annealing, as a function of
the annealing inverse rate . %for different lenghts of the chain. Both
the average and are found to behave
logarithmically for large , but with different exponents, with , and
. We propose a mechanism for
-behavior of based on the Landau-Zener
tunneling theory and on a Fisher's type real-space renormalization group
analysis of the relevant gaps. The model proposed shows therefore a
paradigmatic example of how an adiabatic quantum computation can become very
slow when disorder is at play, even in absence of any source of frustration.Comment: 10 pages, 11 figures; v2: added references, published versio
Quantum dynamics of propagating photons with strong interactions: a generalized input-output formalism
There has been rapid development of systems that yield strong interactions
between freely propagating photons in one dimension via controlled coupling to
quantum emitters. This raises interesting possibilities such as quantum
information processing with photons or quantum many-body states of light, but
treating such systems generally remains a difficult task theoretically. Here,
we describe a novel technique in which the dynamics and correlations of a few
photons can be exactly calculated, based upon knowledge of the initial photonic
state and the solution of the reduced effective dynamics of the quantum
emitters alone. We show that this generalized "input-output" formalism allows
for a straightforward numerical implementation regardless of system details,
such as emitter positions, external driving, and level structure. As a specific
example, we apply our technique to show how atomic systems with infinite-range
interactions and under conditions of electromagnetically induced transparency
enable the selective transmission of correlated multi-photon states
Speeding up critical system dynamics through optimized evolution
The number of defects which are generated on crossing a quantum phase
transition can be minimized by choosing properly designed time-dependent
pulses. In this work we determine what are the ultimate limits of this
optimization. We discuss under which conditions the production of defects
across the phase transition is vanishing small. Furthermore we show that the
minimum time required to enter this regime is , where
is the minimum spectral gap, unveiling an intimate connection between
an optimized unitary dynamics and the intrinsic measure of the Hilbert space
for pure states. Surprisingly, the dynamics is non-adiabatic, this result can
be understood by assuming a simple two-level dynamics for the many-body system.
Finally we classify the possible dynamical regimes in terms of the action
.Comment: 6 pages, 6 figure
Cell Surface Changes of Hemopoietic Cells During Normal and Leukemic Differentiation: An Immuno-Scanning Electron Microscopy Study
Hemopoietic cells display a wide range of cell surface antigens which are either lineage specific or acquired during differentiation. Monoclonal antibodies can be used, in conjunction with colloidal gold markers, to identify under the scanning electron microscopy (SEM) at the single cell level, specific lineage or maturation stages in the hemopoietic bone marrow. Normal bone marrow cells, either gradient separated or purified by immuno-magnetic methods and leukemic cell samples, which can be considered as frozen stages of hemopoietic differentiation, have been studied with this method. Typical cell surface morphologies, which characterize immature progenitor cells and cells committed or differentiated towards the lymphoid, myeloid, erythroid and megakaryocytic lineage have been identified. Correlations between cell surface features and some hemopoietic cells functions have been attempted on the basis of these findings
Breakdown of the adiabatic limit in low dimensional gapless systems
It is generally believed that a generic system can be reversibly transformed
from one state into another by sufficiently slow change of parameters. A
standard argument favoring this assertion is based on a possibility to expand
the energy or the entropy of the system into the Taylor series in the ramp
speed. Here we show that this argumentation is only valid in high enough
dimensions and can break down in low-dimensional gapless systems. We identify
three generic regimes of a system response to a slow ramp: (A) mean-field, (B)
non-analytic, and (C) non-adiabatic. In the last regime the limits of the ramp
speed going to zero and the system size going to infinity do not commute and
the adiabatic process does not exist in the thermodynamic limit. We support our
results by numerical simulations. Our findings can be relevant to
condensed-matter, atomic physics, quantum computing, quantum optics, cosmology
and others.Comment: 11 pages, 5 figures, to appear in Nature Physics (originally
submitted version
One-step bioengineering of magnetic nanoparticles via a surface diazo transfer/azide\u2013alkyne click reaction sequence
We have developed an efficient conversion of amino iron oxides to carbohydrate and protein derived nanoparticles with highly conserved bioactivity through a combination of diazo transfer and azide\u2013alkyne click technolog
Antioxidant properties of agri-food byproducts and specific boosting effects of hydrolytic treatments
Largely produced agri\u2010food byproducts represent a sustainable and easily available
source of phenolic compounds, such as lignins and tannins, endowed with potent antioxidant
properties. We report herein the characterization of the antioxidant properties of nine plant\u2010derived
byproducts. 2,2\u2010Diphenyl\u20101\u2010picrylhydrazyl (DPPH) and ferric reducing/antioxidant power (FRAP)
assays indicated the superior activity of pomegranate peels and seeds, grape pomace and pecan nut
shell. An increase in the antioxidant potency was observed for most of the waste materials following
a hydrolytic treatment, with the exception of the condensed tannin\u2010rich pecan nut shell and grape
pomace. UV\u2010Vis and HPLC investigation of the soluble fractions coupled with the results from IR
analysis and chemical degradation approaches on the whole materials allowed to conclude that the
improvement of the antioxidant properties was due not only to removal of non\u2010active components
(mainly carbohydrates), but also to structural modifications of the phenolic compounds. Parallel
experiments run on natural and bioinspired model phenolic polymers suggested that these
structural modifications positively impacted on the antioxidant properties of lignins and
hydrolyzable tannins, whereas significant degradation of condensed tannin moieties occurred,
likely responsible for the lowering of the reducing power observed for grape pomace and pecan nut
shell. These results open new perspectives toward the exploitation and manipulation of agri\u2010food
byproducts for application as antioxidant additives in functional
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