269 research outputs found
Photon Echoes Produced by Switching Electric Fields
We demonstrate photon echoes in Eu:YSiO by controlling the
inhomogeneous broadening of the Eu
FD optical transition. This transition has
a linear Stark shift and we induce inhomogeneous broadening by applying an
external electric field gradient. After optical excitation, reversing the
polarity of the field rephases the ensemble, resulting in a photon echo. This
is the first demonstration of such a photon echo and its application as a
quantum memory is discussed.Comment: improved introduction, including theoretical outline of the relvant
quantum memory proposa
Quantum Repeaters with Photon Pair Sources and Multi-Mode Memories
We propose a quantum repeater protocol which builds on the well-known DLCZ
protocol [L.M. Duan, M.D. Lukin, J.I. Cirac, and P. Zoller, Nature 414, 413
(2001)], but which uses photon pair sources in combination with memories that
allow to store a large number of temporal modes. We suggest to realize such
multi-mode memories based on the principle of photon echo, using solids doped
with rare-earth ions. The use of multi-mode memories promises a speedup in
entanglement generation by several orders of magnitude and a significant
reduction in stability requirements compared to the DLCZ protocol.Comment: 4 pages, 2 figures, to appear in PRL, accepted versio
Emission of photon echoes in a strongly scattering medium
We observe the two- and three-pulse photon echo emission from a scattering
powder, obtained by grinding a Pr:YSiO rare earth doped single
crystal. We show that the collective emission is coherently constructed over
several grains. A well defined atomic coherence can therefore be created
between randomly placed particles. Observation of photon echo on powders as
opposed to bulk materials opens the way to faster material development. More
generally, time-domain resonant four-wave mixing offers an attractive approach
to investigate coherent propagation in scattering media
Inhibition of Decoherence due to Decay in a Continuum
We propose a scheme for slowing down decay into a continuum. We make use of a
sequence of ultrashort -pulses applied on an auxiliary transition of the
system so that there is a destructive interference between the two transition
amplitudes - one before the application of the pulse and the other after the
application of the pulse. We give explicit results for a structured continuum.
Our scheme can also inhibit unwanted transitions.Comment: 11 pages and 4 figures, submitted to Physical Review Letter
Large two-atom two-photon vacuum Rabi oscillations in a high-quality cavity
We predict a large cooperative effect involving two-atom two-photon vacuum Rabi oscillations in a high-quality cavity. The two-photon emission occurs as a result of simultaneous deexcitation of both atoms with two-photon resonance condition w1 + w2 is about wa + wb , where w1 , w2 are the atomic transition frequencies and wa , wb are the frequencies of the emitted photons. The actual resonance condition depends on the vacuum Rabi couplings. The effect can be realized either with identical atoms in a bimodal cavity or with nonidentical atoms in a single-mode cavity.Peer reviewedPhysic
Quantum memory for photons: I. Dark state polaritons
An ideal and reversible transfer technique for the quantum state between
light and metastable collective states of matter is presented and analyzed in
detail. The method is based on the control of photon propagation in coherently
driven 3-level atomic media, in which the group velocity is adiabatically
reduced to zero. Form-stable coupled excitations of light and matter
(``dark-state polaritons'') associated with the propagation of quantum fields
in Electromagnetically Induced Transparency are identified, their basic
properties discussed and their application for quantum memories for light
analyzed.Comment: 13 pages, 6 figures, paragraph on photon echo adde
Applications of Site-Specific Labeling to Study HAMLET, a Tumoricidal Complex of α-Lactalbumin and Oleic Acid
umor cells), and its tumoricidal activity has been well established.-acetylgalactosaminyltransferase II (ppGalNAc-T2) and further conjugated with aminooxy-derivatives of fluoroprobe or biotin molecules.We found that the molten globule form of hLA and αD-hLA proteins, with or without C-terminal extension, and with and without the conjugated fluoroprobe or biotin molecule, readily form a complex with OA and exhibits tumoricidal activity similar to HAMLET made with full-length hLA protein. The confocal microscopy studies with fluoroprobe-labeled samples show that these proteins are internalized into the cells and found even in the nucleus only when they are complexed with OA. The HAMLET conjugated with a single biotin molecule will be a useful tool to identify the cellular components that are involved with it in the tumoricidal activity
Changes in Proteasome Structure and Function Caused by HAMLET in Tumor Cells
BACKGROUND: Proteasomes control the level of endogenous unfolded proteins by degrading them in the proteolytic core. Insufficient degradation due to altered protein structure or proteasome inhibition may trigger cell death. This study examined the proteasome response to HAMLET, a partially unfolded protein-lipid complex, which is internalized by tumor cells and triggers cell death. METHODOLOGY/PRINCIPAL FINDINGS: HAMLET bound directly to isolated 20S proteasomes in vitro and in tumor cells significant co-localization of HAMLET and 20S proteasomes was detected by confocal microscopy. This interaction was confirmed by co-immunoprecipitation from extracts of HAMLET-treated tumor cells. HAMLET resisted in vitro degradation by proteasomal enzymes and degradation by intact 20S proteasomes was slow compared to fatty acid-free, partially unfolded alpha-lactalbumin. After a brief activation, HAMLET inhibited proteasome activity in vitro and in parallel a change in proteasome structure occurred, with modifications of catalytic (beta1 and beta5) and structural subunits (alpha2, alpha3, alpha6 and beta3). Proteasome inhibition was confirmed in extracts from HAMLET-treated cells and there were indications of proteasome fragmentation in HAMLET-treated cells. CONCLUSIONS/SIGNIFICANCE: The results suggest that internalized HAMLET is targeted to 20S proteasomes, that the complex resists degradation, inhibits proteasome activity and perturbs proteasome structure. We speculate that perturbations of proteasome structure might contribute to the cytotoxic effects of unfolded protein complexes that invade host cells
HAMLET Binding to α-Actinin Facilitates Tumor Cell Detachment
Cell adhesion is tightly regulated by specific molecular interactions and detachment from the extracellular matrix modifies proliferation and survival. HAMLET (Human Alpha-lactalbumin Made LEthal to Tumor cells) is a protein-lipid complex with tumoricidal activity that also triggers tumor cell detachment in vitro and in vivo, suggesting that molecular interactions defining detachment are perturbed in cancer cells. To identify such interactions, cell membrane extracts were used in Far-western blots and HAMLET was shown to bind α-actinins; major F-actin cross-linking proteins and focal adhesion constituents. Synthetic peptide mapping revealed that HAMLET binds to the N-terminal actin-binding domain as well as the integrin-binding domain of α-actinin-4. By co-immunoprecipitation of extracts from HAMLET-treated cancer cells, an interaction with α-actinin-1 and -4 was observed. Inhibition of α-actinin-1 and α-actinin-4 expression by siRNA transfection increased detachment, while α-actinin-4-GFP over-expression significantly delayed rounding up and detachment of tumor cells in response to HAMLET. In response to HAMLET, adherent tumor cells rounded up and detached, suggesting a loss of the actin cytoskeletal organization. These changes were accompanied by a reduction in β1 integrin staining and a decrease in FAK and ERK1/2 phosphorylation, consistent with a disruption of integrin-dependent cell adhesion signaling. Detachment per se did not increase cell death during the 22 hour experimental period, regardless of α-actinin-4 and α-actinin-1 expression levels but adherent cells with low α-actinin levels showed increased death in response to HAMLET. The results suggest that the interaction between HAMLET and α-actinins promotes tumor cell detachment. As α-actinins also associate with signaling molecules, cytoplasmic domains of transmembrane receptors and ion channels, additional α-actinin-dependent mechanisms are discussed
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