1,567 research outputs found
Faithful qubit distribution assisted by one additional qubit against collective noise
We propose a distribution scheme of polarization states of a single photon
over collective-noise channel. By adding one extra photon with a fixed
polarization, we can protect the state against collective noise via a
parity-check measurement and post-selection. While the scheme succeeds only
probabilistically, it is simpler and more flexible than the schemes utilizing
decoherence-free subspace. An application to BB84 protocol through collective
noise channel, which is robust to the Trojan horse attack, is also given.Comment: 4 pages, 3 figures; published version in Phys. Rev. Let
O(N) and USp(N) QCD from String Theory
We propose a holographic dual of large N_c QCD with the gauge group O(N_c)
and USp(N_c) and N_f flavors of massless quarks. This is constructed by adding
O6-planes to an intersecting D4-D8 system in type IIA superstring theory. The
holographic dual description is formulated in the Witten's D4-brane background
with D8-branes and O6-planes embedded in it as probes. The D4-brane background
gives rise to a smooth interpolation of D8-anti-D8 pairs and an O6-anti-O6
pair. We show that the resultant brane configuration explains geometrically the
flavor symmetry breaking patterns in O(N_c) and USp(N_c) QCD that are caused by
quark bilinear condensates.
We next discuss that baryons can be realized as D4-anti-D4 pairs wrapped on
S^4 that intersect with the O6-plane. By analyzing the tachyons on it, we
reproduce the stability conditions of the baryons that are expected from the
gauge theory viewpoint. The stable baryon configurations are classified
systematically by using K-theory. We also give a similar analysis for the flux
tubes and again reproduce the results that are consistent with QCD.Comment: 20 pages, 2 figures, v2: discussions of flux tubes clarified,
references added, v3: minor changes, final version published in PT
Boosting up quantum key distribution by learning statistics of practical single photon sources
We propose a simple quantum-key-distribution (QKD) scheme for practical
single photon sources (SPSs), which works even with a moderate suppression of
the second-order correlation of the source. The scheme utilizes a
passive preparation of a decoy state by monitoring a fraction of the signal via
an additional beam splitter and a detector at the sender's side to monitor
photon number splitting attacks. We show that the achievable distance increases
with the precision with which the sub-Poissonian tendency is confirmed in
higher photon number distribution of the source, rather than with actual
suppression of the multi-photon emission events. We present an example of the
secure key generation rate in the case of a poor SPS with , in
which no secure key is produced with the conventional QKD scheme, and show that
learning the photon-number distribution up to several numbers is sufficient for
achieving almost the same achievable distance as that of an ideal SPS.Comment: 11 pages, 3 figures; published version in New J. Phy
Experimental ancilla-assisted qubit transmission against correlated noise using quantum parity checking
We report the experimental demonstration of a transmission scheme of photonic
qubits over unstabilized optical fibers, which has the plug-and-play feature as
well as the ability to transmit any state of a qubit, regardless of whether it
is known, unknown, or entangled to other systems. A high fidelity to the
noiseless quantum channel was achieved by adding an ancilla photon after the
signal photon within the correlation time of the fiber noise and by performing
quantum parity checking. Simplicity, maintenance-free feature and robustness
against path-length mismatches among the nodes make our scheme suitable for
multi-user quantum communication networks.Comment: 8 pages, 4 figures; published in New J. Phys. and selected in IOP
Selec
Structure and Dynamics of Water at the Water-Air Interface Using First-Principles Molecular Dynamics Simulations. II. NonLocal vs Empirical van der Waals Corrections
Human autologous culture expanded bone marrow mesenchymal cell transplantation for repair of cartilage defects in osteoarthritic knees
AbstractObjective There is no widely accepted method to repair articular cartilage defects. Bone marrow mesenchymal cells have the potential to differentiate into bone, cartilage, fat and muscle. Bone marrow mesenchymal cell transplantation is easy to use clinically because cells can be easily obtained and can be multiplied without losing their capacity of differentiation. The objective of this study was to apply these cell transplantations to repair human articular cartilage defects in osteoarthritic knee joints.Design Twenty-four knees of 24 patients with knee osteoarthritis (OA) who underwent a high tibial osteotomy comprised the study group. Adherent cells in bone marrow aspirates were culture expanded, embedded in collagen gel, transplanted into the articular cartilage defect in the medial femoral condyle and covered with autologous periosteum at the time of 12 high tibial osteotomies. The other 12 subjects served as cell-free controls.Results In the cell-transplanted group, as early as 6.3 weeks after transplantation the defects were covered with white to pink soft tissue, in which metachromasia was partially observed. Forty-two weeks after transplantation, the defects were covered with white soft tissue, in which metachromasia was observed in almost all areas of the sampled tissue and hyaline cartilage-like tissue was partially observed. Although the clinical improvement was not significantly different, the arthroscopic and histological grading score was better in the cell-transplanted group than in the cell-free control group.Conclusions This procedure highlights the availability of autologous culture expanded bone marrow mesenchymal cell transplantation for the repair of articular cartilage defects in humans
Anomalous time delays and quantum weak measurements in optical micro-resonators
We study inelastic resonant scattering of a Gaussian wave packet with the
parameters close to a zero of the complex scattering coefficient. We
demonstrate, both theoretically and experimentally, that such near-zero
scattering can result in anomalously-large time delays and frequency shifts of
the scattered wave packet. Furthermore, we reveal a close analogy of these
anomalous shifts with the spatial and angular Goos-H\"anchen optical beam
shifts, which are amplified via quantum weak measurements. However, in contrast
to other beam-shift and weak-measurement systems, we deal with a
one-dimensional scalar wave without any intrinsic degrees of freedom. It is the
non-Hermitian nature of the system that produces its rich and non-trivial
behaviour. Our results are generic for any scattering problem, either quantum
or classical. As an example, we consider the transmission of an optical pulse
through a nano-fiber with a side-coupled toroidal micro-resonator. The zero of
the transmission coefficient corresponds to the critical coupling conditions.
Experimental measurements of the time delays near the critical-coupling
parameters verify our weak-measurement theory and demonstrate amplification of
the time delay from the typical inverse resonator linewidth scale to the pulse
duration scale.Comment: 14 pages, 5 figure
Exploiting the quantum Zeno effect to beat photon loss in linear optical quantum information processors
We devise a new technique to enhance transmission of quantum information
through linear optical quantum information processors. The idea is based on
applying the Quantum Zeno effect to the process of photon absorption. By
frequently monitoring the presence of the photon through a QND (quantum
non-demolition) measurement the absorption is suppressed. Quantum information
is encoded in the polarization degrees of freedom and is therefore not affected
by the measurement. Some implementations of the QND measurement are proposed.Comment: 4 pages, 1 figur
Accurate molecular orientation at interfaces determined by multimode polarization-dependent heterodyne-detected sum-frequency generation spectroscopy via multidimensional orientational distribution function
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