97 research outputs found
Decision problems with quantum black boxes
We examine how to distinguish between unitary operators, when the exact form
of the possible operators is not known. Instead we are supplied with "programs"
in the form of unitary transforms, which can be used as references for
identifying the unknown unitary transform. All unitary transforms should be
used as few times as possible. This situation is analoguous to programmable
state discrimination. One difference, however, is that the quantum state to
which we apply the unitary transforms may be entangled, leading to a richer
variety of possible strategies. By suitable selection of an input state and
generalized measurement of the output state, both unambiguous and minimum-error
discrimination can be achieved. Pairwise comparison of operators, comparing
each transform to be identified with a program transform, is often a useful
strategy. There are, however, situations in which more complicated strategies
perform better. This is the case especially when the number of allowed
applications of program operations is different from the number of the
transforms to be identified
Continuous Variable Quantum Cryptography using Two-Way Quantum Communication
Quantum cryptography has been recently extended to continuous variable
systems, e.g., the bosonic modes of the electromagnetic field. In particular,
several cryptographic protocols have been proposed and experimentally
implemented using bosonic modes with Gaussian statistics. Such protocols have
shown the possibility of reaching very high secret-key rates, even in the
presence of strong losses in the quantum communication channel. Despite this
robustness to loss, their security can be affected by more general attacks
where extra Gaussian noise is introduced by the eavesdropper. In this general
scenario we show a "hardware solution" for enhancing the security thresholds of
these protocols. This is possible by extending them to a two-way quantum
communication where subsequent uses of the quantum channel are suitably
combined. In the resulting two-way schemes, one of the honest parties assists
the secret encoding of the other with the chance of a non-trivial superadditive
enhancement of the security thresholds. Such results enable the extension of
quantum cryptography to more complex quantum communications.Comment: 12 pages, 7 figures, REVTe
Experimental GHZ Entanglement beyond Qubits
The Greenberger-Horne-Zeilinger (GHZ) argument provides an all-or-nothing
contradiction between quantum mechanics and local-realistic theories. In its
original formulation, GHZ investigated three and four particles entangled in
two dimensions only. Very recently, higher dimensional contradictions
especially in three dimensions and three particles have been discovered but it
has remained unclear how to produce such states. In this article we
experimentally show how to generate a three-dimensional GHZ state from
two-photon orbital-angular-momentum entanglement. The first suggestion for a
setup which generates three-dimensional GHZ entanglement from these entangled
pairs came from using the computer algorithm Melvin. The procedure employs
novel concepts significantly beyond the qubit case. Our experiment opens up the
possibility of a truly high-dimensional test of the GHZ-contradiction which,
interestingly, employs non-Hermitian operators.Comment: 6+6 pages, 8 figure
Size and surface charge of gold nanoparticles determine absorption across intestinal barriers and accumulation in secondary target organs after oral administration
It is of urgent need to identify the exact physico-chemical characteristics which allow maximum uptake and accumulation in secondary target organs of nanoparticulate drug delivery systems after oral ingestion. We administered radiolabelled gold nanoparticles in different sizes (1.4-200 nm) with negative surface charge and 2.8 nm nanoparticles with opposite surface charges by intra-oesophageal instillation into healthy adult female rats. The quantitative amount of the particles in organs, tissues and excrements was measured after 24 h by gamma-spectroscopy. The highest accumulation in secondary organs was mostly found for 1.4 nm particles; the negatively charged particles were accumulated mostly more than positively charged particles. Importantly, 18 nm particles show a higher accumulation in brain and heart compared to other sized particles. No general rule accumulation can be made so far. Therefore, specialized drug delivery systems via the oral route have to be individually designed, depending on the respective target organ
Correlations vs connectivity in R-charge
The holographic relation between quantum correlations and connectivity of
spacetime is explored for single R-charged AdS black holes and their
half-BPS limits (superstars). In a two boundary set-up, the wormhole between
both universes reduces to a designable and computable quantum mechanical
correlation between the dual microscopic degrees of freedom in the BPS limit.
This quantum connectivity is seen as a naked singularity by a single sided
observer. In a single boundary set-up, as a small step towards the description
of entangled black holes, we describe quantum teleportation between two labs in
different locations of the transverse 5-sphere using entangled gravitons in a
reference state that provides a classical channel between both labs.Comment: 53 pages + appendices, 29 figures v2: few corrections and added a
conclusion sectio
Synthesis and Oral Uptake Studies of Lipidic and Glyco-Lipidic Conjugates of Beta-Lactam Antibiotics
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