13,841 research outputs found
Gaussian bosonic synergy: quantum communication via realistic channels of zero quantum capacity
As with classical information, error-correcting codes enable reliable
transmission of quantum information through noisy or lossy channels. In
contrast to the classical theory, imperfect quantum channels exhibit a strong
kind of synergy: there exist pairs of discrete memoryless quantum channels,
each of zero quantum capacity, which acquire positive quantum capacity when
used together. Here we show that this "superactivation" phenomenon also occurs
in the more realistic setting of optical channels with attenuation and Gaussian
noise. This paves the way for its experimental realization and application in
real-world communications systems.Comment: 5 pages, 4 figures, one appendi
New lower bounds to the output entropy of multi-mode quantum Gaussian channels
We prove that quantum thermal Gaussian input states minimize the output
entropy of the multi-mode quantum Gaussian attenuators and amplifiers that are
entanglement breaking and of the multi-mode quantum Gaussian phase
contravariant channels among all the input states with a given entropy. This is
the first time that this property is proven for a multi-mode channel without
restrictions on the input states. A striking consequence of this result is a
new lower bound on the output entropy of all the multi-mode quantum Gaussian
attenuators and amplifiers in terms of the input entropy. We apply this bound
to determine new upper bounds to the communication rates in two different
scenarios. The first is classical communication to two receivers with the
quantum degraded Gaussian broadcast channel. The second is the simultaneous
classical communication, quantum communication and entanglement generation or
the simultaneous public classical communication, private classical
communication and quantum key distribution with the Gaussian quantum-limited
attenuator
Gaussian states minimize the output entropy of one-mode quantum Gaussian channels
We prove the longstanding conjecture stating that Gaussian thermal input
states minimize the output von Neumann entropy of one-mode phase-covariant
quantum Gaussian channels among all the input states with a given entropy.
Phase-covariant quantum Gaussian channels model the attenuation and the noise
that affect any electromagnetic signal in the quantum regime. Our result is
crucial to prove the converse theorems for both the triple trade-off region and
the capacity region for broadcast communication of the Gaussian quantum-limited
amplifier. Our result extends to the quantum regime the Entropy Power
Inequality that plays a key role in classical information theory. Our proof
exploits a completely new technique based on the recent determination of the
p->q norms of the quantum-limited amplifier [De Palma et al.,
arXiv:1610.09967]. This technique can be applied to any quantum channel
Application of Space-Time Diversity/Coding For Power Line Channels
The purpose of the present work is to evaluate the application of space-time block codes to the transmission of digital data over the power-line communication channel (PLC). Data transmitted over the power-line channel is usually corrupted by impulsive noise. In this work we analyse
the performance of space-time block codes in this type of environment and show that a significant performance gain can be achieved at almost no processing expense
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