7,923 research outputs found
Quantum Entangled Supercorrelated States in the Jaynes-Cummings Model
The regions of independent quantum states, maximally classically correlated
states, and purely quantum entangled (supercorrelated) states described in a
recent formulation of quantum information theory by Cerf and Adami are explored
here numerically in the parameter space of the well-known exactly soluable
Jaynes-Cummings model for equilibrium and nonequilibrium time-dependent
ensembles.Comment: 12 pages, 3 figure
Bell's inequality with Dirac particles
We study Bell's inequality using the Bell states constructed from four
component Dirac spinors. Spin operator is related to the Pauli-Lubanski pseudo
vector which is relativistic invariant operator. By using Lorentz
transformation, in both Bell states and spin operator, we obtain an observer
independent Bell's inequality, so that it is maximally violated as long as it
is violated maximally in the rest frame.Comment: 7 pages. arXiv admin note: text overlap with arXiv:quant-ph/0308156
by other author
The future burden of cancer in London compared with England.
BACKGROUND: The future burden of cancer in England is predicted to increase by 33% by 2020. Those planning health services are often interested in predictions at a local level. This study aimed to estimate the future burden of cancer in London and compare this with estimates for England. METHODS: Predictions for London were based on cancer registration data (1985-2003) and population projections up until 2024. The number of future cases and age-standardized incidence rates (ASRs) were projected using an age-period-cohort model developed for the analysis of cancer trends and projections in the Nordic countries. Estimates for England were taken from an earlier publication. RESULTS: In London, ASRs for all cancers (excluding non-melanoma skin cancer) decreased for both sexes, whereas in England, ASRs decreased in males and increased slightly in females. In London, the number of cases for both sexes is predicted to increase from approximately 27,000 in 2002 to approximately 28,500 in 2022, an increase of 5%. In England, a greater increase is predicted, from approximately 224,000 in 2001 to approximately 299,000 in 2020, an increase of 33%. CONCLUSIONS: Projections of the future burden of cancer are particularly sensitive to demographic population trends. They are likely to be different for cities compared with rural areas or entire countries
Entropic bounds on coding for noisy quantum channels
In analogy with its classical counterpart, a noisy quantum channel is
characterized by a loss, a quantity that depends on the channel input and the
quantum operation performed by the channel. The loss reflects the transmission
quality: if the loss is zero, quantum information can be perfectly transmitted
at a rate measured by the quantum source entropy. By using block coding based
on sequences of n entangled symbols, the average loss (defined as the overall
loss of the joint n-symbol channel divided by n, when n tends to infinity) can
be made lower than the loss for a single use of the channel. In this context,
we examine several upper bounds on the rate at which quantum information can be
transmitted reliably via a noisy channel, that is, with an asymptotically
vanishing average loss while the one-symbol loss of the channel is non-zero.
These bounds on the channel capacity rely on the entropic Singleton bound on
quantum error-correcting codes [Phys. Rev. A 56, 1721 (1997)]. Finally, we
analyze the Singleton bounds when the noisy quantum channel is supplemented
with a classical auxiliary channel.Comment: 20 pages RevTeX, 10 Postscript figures. Expanded Section II, added 1
figure, changed title. To appear in Phys. Rev. A (May 98
Quantum discord and local demons
Quantum discord was proposed as a measure of the "quantumness" of
correlations. There are at least three different discord-like quantities, two
of which determine the difference between the efficiencies of a Szilard's
engine under different sets of restrictions. The three discord measures vanish
simulataneosly. We introduce an easy way to test for zero discord, relate it to
the Cerf-Adami conditional entropy and show that there is no relation between
the discord and the local disitnguishability.Comment: 7 pages, RevTeX. Some minor changes after comments from colleagues,
some references added. Similar to published versio
Selective pressures on genomes in molecular evolution
We describe the evolution of macromolecules as an information transmission
process and apply tools from Shannon information theory to it. This allows us
to isolate three independent, competing selective pressures that we term
compression, transmission, and neutrality selection. The first two affect
genome length: the pressure to conserve resources by compressing the code, and
the pressure to acquire additional information that improves the channel,
increasing the rate of information transmission into each offspring. Noisy
transmission channels (replication with mutations) gives rise to a third
pressure that acts on the actual encoding of information; it maximizes the
fraction of mutations that are neutral with respect to the phenotype. This
neutrality selection has important implications for the evolution of
evolvability. We demonstrate each selective pressure in experiments with
digital organisms.Comment: 16 pages, 3 figures, to be published in J. theor. Biolog
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