9,593 research outputs found
Entropy exchange and entanglement in the Jaynes-Cummings model
The Jaynes-Cummings model is the simplest fully quantum model that describes
the interaction between light and matter. We extend a previous analysis by
Phoenix and Knight (S. J. D. Phoenix, P. L. Knight, Annals of Physics 186,
381). of the JCM by considering mixed states of both the light and matter. We
present examples of qualitatively different entropic correlations. In
particular, we explore the regime of entropy exchange between light and matter,
i.e. where the rate of change of the two are anti-correlated. This behavior
contrasts with the case of pure light-matter states in which the rate of change
of the two entropies are positively correlated and in fact identical. We give
an analytical derivation of the anti-correlation phenomenon and discuss the
regime of its validity. Finally, we show a strong correlation between the
region of the Bloch sphere characterized by entropy exchange and that
characterized by minimal entanglement as measured by the negative eigenvalues
of the partially transposed density matrix.Comment: 8 pages, 5 figure
Deterministic Quantum Key Distribution Using Gaussian-Modulated Squeezed States
A continuous variable ping-pong scheme, which is utilized to generate
deterministically private key, is proposed. The proposed scheme is implemented
physically by using Gaussian-modulated squeezed states. The deterministic way,
i.e., no basis reconciliation between two parties, leads a two-times efficiency
comparing to the standard quantum key distribution schemes. Especially, the
separate control mode does not need in the proposed scheme so that it is
simpler and more available than previous ping-pong schemes. The attacker may be
detected easily through the fidelity of the transmitted signal, and may not be
successful in the beam splitter attack strategy.Comment: 7 pages, 4figure
Information Theory based on Non-additive Information Content
We generalize the Shannon's information theory in a nonadditive way by
focusing on the source coding theorem. The nonadditive information content we
adopted is consistent with the concept of the form invariance structure of the
nonextensive entropy. Some general properties of the nonadditive information
entropy are studied, in addition, the relation between the nonadditivity
and the codeword length is pointed out.Comment: 9 pages, no figures, RevTex, accepted for publication in Phys. Rev.
E(an error in proof of theorem 1 was corrected, typos corrected
On the classical capacity of quantum Gaussian channels
The set of quantum Gaussian channels acting on one bosonic mode can be
classified according to the action of the group of Gaussian unitaries. We look
for bounds on the classical capacity for channels belonging to such a
classification. Lower bounds can be efficiently calculated by restricting to
Gaussian encodings, for which we provide analytical expressions.Comment: 10 pages, IOP style. v2: minor corrections, close to the published
versio
Quantum key distribution with delayed privacy amplification and its application to security proof of a two-way deterministic protocol
Privacy amplification (PA) is an essential post-processing step in quantum
key distribution (QKD) for removing any information an eavesdropper may have on
the final secret key. In this paper, we consider delaying PA of the final key
after its use in one-time pad encryption and prove its security. We prove that
the security and the key generation rate are not affected by delaying PA.
Delaying PA has two applications: it serves as a tool for significantly
simplifying the security proof of QKD with a two-way quantum channel, and also
it is useful in QKD networks with trusted relays. To illustrate the power of
the delayed PA idea, we use it to prove the security of a qubit-based two-way
deterministic QKD protocol which uses four states and four encoding operations.Comment: 11 pages, 3 figure
Dynamical response of the Hodgkin-Huxley model in the high-input regime
The response of the Hodgkin-Huxley neuronal model subjected to stochastic
uncorrelated spike trains originating from a large number of inhibitory and
excitatory post-synaptic potentials is analyzed in detail. The model is
examined in its three fundamental dynamical regimes: silence, bistability and
repetitive firing. Its response is characterized in terms of statistical
indicators (interspike-interval distributions and their first moments) as well
as of dynamical indicators (autocorrelation functions and conditional
entropies). In the silent regime, the coexistence of two different coherence
resonances is revealed: one occurs at quite low noise and is related to the
stimulation of subthreshold oscillations around the rest state; the second one
(at intermediate noise variance) is associated with the regularization of the
sequence of spikes emitted by the neuron. Bistability in the low noise limit
can be interpreted in terms of jumping processes across barriers activated by
stochastic fluctuations. In the repetitive firing regime a maximization of
incoherence is observed at finite noise variance. Finally, the mechanisms
responsible for spike triggering in the various regimes are clearly identified.Comment: 14 pages, 24 figures in eps, submitted to Physical Review
Finite-Connectivity Spin-Glass Phase Diagrams and Low Density Parity Check Codes
We obtain phase diagrams of regular and irregular finite connectivity
spin-glasses. Contact is firstly established between properties of the phase
diagram and the performances of low density parity check codes (LDPC) within
the Replica Symmetric (RS) ansatz. We then study the location of the dynamical
and critical transition of these systems within the one step Replica Symmetry
Breaking theory (RSB), extending similar calculations that have been performed
in the past for the Bethe spin-glass problem. We observe that, away from the
Nishimori line, in the low temperature region, the location of the dynamical
transition line does change within the RSB theory, in comparison with the (RS)
case. For LDPC decoding over the binary erasure channel we find, at zero
temperature and rate R=1/4 an RS critical transition point located at p_c =
0.67 while the critical RSB transition point is located at p_c = 0.7450, to be
compared with the corresponding Shannon bound 1-R. For the binary symmetric
channel (BSC) we show that the low temperature reentrant behavior of the
dynamical transition line, observed within the RS ansatz, changes within the
RSB theory; the location of the dynamical transition point occurring at higher
values of the channel noise. Possible practical implications to improve the
performances of the state-of-the-art error correcting codes are discussed.Comment: 21 pages, 15 figure
Entropic Entanglement Criteria for Continuous Variables
We derive several entanglement criteria for bipartite continuous variable
quantum systems based on the Shannon entropy. These criteria are more sensitive
than those involving only second-order moments, and are equivalent to
well-known variance product tests in the case of Gaussian states. Furthermore,
they involve only a pair of quadrature measurements, and will thus should prove
extremely useful the experimental identification of entanglement.Comment: 4 pages, 2 figure
Lost at Sea in Search of a Diagnosis: A Case of Unexplained Bleeding
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134475/1/pbc25980_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134475/2/pbc25980.pd
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