5,515 research outputs found
Can Classical Noise Enhance Quantum Transmission?
A modified quantum teleportation protocol broadens the scope of the classical
forbidden-interval theorems for stochastic resonance. The fidelity measures
performance of quantum communication. The sender encodes the two classical bits
for quantum teleportation as weak bipolar subthreshold signals and sends them
over a noisy classical channel. Two forbidden-interval theorems provide a
necessary and sufficient condition for the occurrence of the nonmonotone
stochastic resonance effect in the fidelity of quantum teleportation. The
condition is that the noise mean must fall outside a forbidden interval related
to the detection threshold and signal value. An optimal amount of classical
noise benefits quantum communication when the sender transmits weak signals,
the receiver detects with a high threshold, and the noise mean lies outside the
forbidden interval. Theorems and simulations demonstrate that both
finite-variance and infinite-variance noise benefit the fidelity of quantum
teleportation.Comment: 11 pages, 3 figures, replaced with published version that includes
new section on imperfect entanglement and references to J. J. Ting's earlier
wor
Stochastic resonance in Gaussian quantum channels
We determine conditions for the presence of stochastic resonance in a lossy
bosonic channel with a nonlinear, threshold decoding. The stochastic resonance
effect occurs if and only if the detection threshold is outside of a "forbidden
interval". We show that it takes place in different settings: when transmitting
classical messages through a lossy bosonic channel, when transmitting over an
entanglement-assisted lossy bosonic channel, and when discriminating channels
with different loss parameters. Moreover, we consider a setting in which
stochastic resonance occurs in the transmission of a qubit over a lossy bosonic
channel with a particular encoding and decoding. In all cases, we assume the
addition of Gaussian noise to the signal and show that it does not matter who,
between sender and receiver, introduces such a noise. Remarkably, different
results are obtained when considering a setting for private communication. In
this case the symmetry between sender and receiver is broken and the "forbidden
interval" may vanish, leading to the occurrence of stochastic resonance effects
for any value of the detection threshold.Comment: 17 pages, 6 figures. Manuscript improved in many ways. New results on
private communication adde
Joint source-channel coding for a quantum multiple access channel
Suppose that two senders each obtain one share of the output of a classical,
bivariate, correlated information source. They would like to transmit the
correlated source to a receiver using a quantum multiple access channel. In
prior work, Cover, El Gamal, and Salehi provided a combined source-channel
coding strategy for a classical multiple access channel which outperforms the
simpler "separation" strategy where separate codebooks are used for the source
coding and the channel coding tasks. In the present paper, we prove that a
coding strategy similar to the Cover-El Gamal-Salehi strategy and a
corresponding quantum simultaneous decoder allow for the reliable transmission
of a source over a quantum multiple access channel, as long as a set of
information inequalities involving the Holevo quantity hold.Comment: 21 pages, v2: minor changes, accepted into Journal of Physics
Entanglement-Assisted Quantum Error Correction with Linear Optics
We construct a theory of continuous-variable entanglement-assisted quantum
error correction. We present an example of a continuous-variable
entanglement-assisted code that corrects for an arbitrary single-mode error. We
also show how to implement encoding circuits using passive optical devices,
homodyne measurements, feedforward classical communication, conditional
displacements, and off-line squeezers.Comment: 8 pages, 1 figure, major expansion of paper with detailed exampl
The squashed entanglement of the noiseless quantum Gaussian attenuator and amplifier
We determine the maximum squashed entanglement achievable between sender and
receiver of the noiseless quantum Gaussian attenuators and amplifiers and we
prove that it is achieved sending half of an infinitely squeezed two-mode
vacuum state. The key ingredient of the proof is a lower bound to the squashed
entanglement of the quantum Gaussian states obtained applying a two-mode
squeezing operation to a quantum thermal Gaussian state tensored with the
vacuum state. This is the first lower bound to the squashed entanglement of a
quantum Gaussian state and opens the way to determine the squashed entanglement
of all quantum Gaussian channels. Moreover, we determine the classical squashed
entanglement of the quantum Gaussian states above and show that it is strictly
larger than their squashed entanglement. This is the first time that the
classical squashed entanglement of a mixed quantum Gaussian state is
determined
Fisrt report of indigenous Dermacentor reticulatus populations in Belgium and preliminary study on associated Babesiosis pathogens
Conditional decoupling of quantum information
Insights from quantum information theory show that correlation measures based on quantum entropy are fundamental tools that reveal the entanglement structure of multipartite states. In that spirit, Groisman, Popescu, and Winter [Phys. Rev. A 72, 032317 (2005)PLRAAN1050-294710.1103/PhysRevA.72.032317] showed that the quantum mutual information I(A;B) quantifies the minimal rate of noise needed to erase the correlations in a bipartite state of quantum systems AB. Here, we investigate correlations in tripartite systems ABE. In particular, we are interested in the minimal rate of noise needed to apply to the systems AE in order to erase the correlations between A and B given the information in system E, in such a way that there is only negligible disturbance on the marginal BE. We present two such models of conditional decoupling, called deconstruction and conditional erasure cost of tripartite states ABE. Our main result is that both are equal to the conditional quantum mutual information I(A;B|E) - establishing it as an operational measure for tripartite quantum correlations
Geothermal probabilistic cost study
A tool is presented to quantify the risks of geothermal projects, the Geothermal Probabilistic Cost Model (GPCM). The GPCM model was used to evaluate a geothermal reservoir for a binary-cycle electric plant at Heber, California. Three institutional aspects of the geothermal risk which can shift the risk among different agents was analyzed. The leasing of geothermal land, contracting between the producer and the user of the geothermal heat, and insurance against faulty performance were examined
Optimal tests for continuous-variable quantum teleportation and photodetectors
Quantum teleportation is a primitive in several important applications,
including quantum communication, quantum computation, error correction, and
quantum networks. In this work, we propose an optimal test for the performance
of continuous-variable (CV) quantum teleportation in terms of the
energy-constrained channel fidelity between ideal CV teleportation and its
experimental implementation. All work prior to ours considered suboptimal tests
of the performance of CV teleportation, focusing instead on its performance for
particular states, such as ensembles of coherent states, squeezed states, cat
states, etc. Here we prove that the optimal state for testing CV teleportation
is an entangled superposition of twin-Fock states. We establish this result by
reducing the problem of estimating the energy-constrained channel fidelity
between ideal CV teleportation and its experimental approximation to a
quadratic program and solving it. As an additional result, we obtain an
analytical solution to the energy-constrained diamond distance between a
photodetector and its experimental approximation. These results are relevant
for experiments that make use of CV teleportation and photodetectors.Comment: 20 pages, 3 figure
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