6 research outputs found
Fidelity threshold for long-range entanglement in quantum networks
We present a strategy to generate long-range entanglement in noisy quantum
networks. We consider a cubic lattice whose bonds are partially entangled mixed
states of two qubits, and where quantum operations can be applied perfectly at
the nodes. In contrast to protocols designed for one- or two-dimensional
regular lattices, we find that entanglement can be created between arbitrarily
distant qubits if the fidelity of the bonds is higher than a critical value,
independent of the system size. Therefore, we show that a constant overhead of
local resources, together with connections of finite fidelity, is sufficient to
achieve long-distance quantum communication in noisy networks.Comment: published versio
Statistical significance of quantitative PCR
BACKGROUND: PCR has the potential to detect and precisely quantify specific DNA sequences, but it is not yet often used as a fully quantitative method. A number of data collection and processing strategies have been described for the implementation of quantitative PCR. However, they can be experimentally cumbersome, their relative performances have not been evaluated systematically, and they often remain poorly validated statistically and/or experimentally. In this study, we evaluated the performance of known methods, and compared them with newly developed data processing strategies in terms of resolution, precision and robustness.
RESULTS: Our results indicate that simple methods that do not rely on the estimation of the efficiency of the PCR amplification may provide reproducible and sensitive data, but that they do not quantify DNA with precision. Other evaluated methods based on sigmoidal or exponential curve fitting were generally of both poor resolution and precision. A statistical analysis of the parameters that influence efficiency indicated that it depends mostly on the selected amplicon and to a lesser extent on the particular biological sample analyzed. Thus, we devised various strategies based on individual or averaged efficiency values, which were used to assess the regulated expression of several genes in response to a growth factor.
CONCLUSION: Overall, qPCR data analysis methods differ significantly in their performance, and this analysis identifies methods that provide DNA quantification estimates of high precision, robustness and reliability. These methods allow reliable estimations of relative expression ratio of two-fold or higher, and our analysis provides an estimation of the number of biological samples that have to be analyzed to achieve a given precision
Quantum random networks
In recent years, new algorithms and cryptographic protocols based on the laws
of quantum physics have been designed to outperform classical communication and
computation. We show that the quantum world also opens up new perspectives in
the field of complex networks. Already the simplest model of a classical random
network changes dramatically when extended to the quantum case, as we obtain a
completely distinct behavior of the critical probabilities at which different
subgraphs appear. In particular, in a network of N nodes, any quantum subgraph
can be generated by local operations and classical communication if the
entanglement between pairs of nodes scales as 1/N^2.Comment: 5 pages, 4 figures, 1 tabl
Entanglement distribution in pure-state quantum networks
We investigate entanglement distribution in pure-state quantum networks. We
consider the case when non-maximally entangled two-qubit pure states are shared
by neighboring nodes of the network. For a given pair of nodes, we investigate
how to generate the maximal entanglement between them by performing local
measurements, assisted by classical communication, on the other nodes. We find
optimal measurement protocols for both small and large 1D networks. Quite
surprisingly, we prove that Bell measurements are not always the optimal ones
to perform in such networks. We generalize then the results to simple small 2D
networks, finding again counter-intuitive optimal measurement strategies.
Finally, we consider large networks with hierarchical lattice geometries and 2D
networks. We prove that perfect entanglement can be established on large
distances with probability one in a finite number of steps, provided the
initial entanglement shared by neighboring nodes is large enough. We discuss
also various protocols of entanglement distribution in 2D networks employing
classical and quantum percolation strategies.Comment: revtex4, 14 pages, 15 figures (.eps), submitted for publicatio