1,956 research outputs found
Publicness, Privacy and Confidentiality in the Single-Serving Quantum Broadcast Channel
The 2-receiver broadcast channel is studied: a network with three parties
where the transmitter and one of the receivers are the primarily involved
parties and the other receiver considered as third party. The messages that are
determined to be communicated are classified into public, private and
confidential based on the information they convey. The public message contains
information intended for both parties and is required to be decoded correctly
by both of them, the private message is intended for the primary party only,
however, there is no secrecy requirement imposed upon it meaning that it can
possibly be exposed to the third party and finally the confidential message
containing information intended exclusively for the primary party such that
this information must be kept completely secret from the other receiver. A
trade-off arises between the rates of the three messages, when one of the rates
is high, the other rates may need to be reduced to guarantee the reliable
transmission of all three messages. The encoder performs the necessary
equivocation by virtue of dummy random numbers whose rate is assumed to be
limited and should be considered in the trade-off as well. We study this
trade-off in the one-shot regime of a quantum broadcast channel by providing
achievability and (weak) converse regions. In the achievability, we prove and
use a conditional version of the convex-split lemma as well as position-based
decoding. By studying the asymptotic behaviour of our bounds, we will recover
several well-known asymptotic results in the literature.Comment: 23 pages, 1 figure, journa
Trade-off coding for universal qudit cloners motivated by the Unruh effect
A "triple trade-off" capacity region of a noisy quantum channel provides a
more complete description of its capabilities than does a single capacity
formula. However, few full descriptions of a channel's ability have been given
due to the difficult nature of the calculation of such regions---it may demand
an optimization of information-theoretic quantities over an infinite number of
channel uses. This work analyzes the d-dimensional Unruh channel, a noisy
quantum channel which emerges in relativistic quantum information theory. We
show that this channel belongs to the class of quantum channels whose capacity
region requires an optimization over a single channel use, and as such is
tractable. We determine two triple-trade off regions, the quantum dynamic
capacity region and the private dynamic capacity region, of the d-dimensional
Unruh channel. Our results show that the set of achievable rate triples using
this coding strategy is larger than the set achieved using a time-sharing
strategy. Furthermore, we prove that the Unruh channel has a distinct structure
made up of universal qudit cloning channels, thus providing a clear
relationship between this relativistic channel and the process of stimulated
emission present in quantum optical amplifiers.Comment: 26 pages, 4 figures; v2 has minor corrections to Definition 2.
Definition 4 and Remark 5 have been adde
One-shot capacity bounds on the simultaneous transmission of classical and quantum information
© 1963-2012 IEEE. We study the communication capabilities of a quantum channel under the most general channel model known as the one-shot model. Unlike classical channels that can only be used to transmit classical information (bits), a quantum channel can be used for transmission of classical information, quantum information (qubits) and simultaneous transmission of classical and quantum information. In this work, we investigate the one-shot capabilities of a quantum channel for simultaneously transmitting bits and qubits. This problem was studied in the asymptotic regime for a memoryless channel where a regularized characterization of the capacity region was reported. It is known that the transmission of private classical information is closely related to the problem of quantum information transmission. We resort to this idea and find achievable and converse bounds on the simultaneous transmission of the public and private classical information. Then shifting the classical private rate to the quantum information rate leads to a rate region for simultaneous transmission of classical and quantum information. In the case of asymptotic i.i.d. setting, our one-shot result is evaluated to the known results in the literature. Our main tools used in the achievability proofs are position-based decoding and convex-split lemma
Trade-off capacities of the quantum Hadamard channels
Coding theorems in quantum Shannon theory express the ultimate rates at which
a sender can transmit information over a noisy quantum channel. More often than
not, the known formulas expressing these transmission rates are intractable,
requiring an optimization over an infinite number of uses of the channel.
Researchers have rarely found quantum channels with a tractable classical or
quantum capacity, but when such a finding occurs, it demonstrates a complete
understanding of that channel's capabilities for transmitting classical or
quantum information. Here, we show that the three-dimensional capacity region
for entanglement-assisted transmission of classical and quantum information is
tractable for the Hadamard class of channels. Examples of Hadamard channels
include generalized dephasing channels, cloning channels, and the Unruh
channel. The generalized dephasing channels and the cloning channels are
natural processes that occur in quantum systems through the loss of quantum
coherence or stimulated emission, respectively. The Unruh channel is a noisy
process that occurs in relativistic quantum information theory as a result of
the Unruh effect and bears a strong relationship to the cloning channels. We
give exact formulas for the entanglement-assisted classical and quantum
communication capacity regions of these channels. The coding strategy for each
of these examples is superior to a naive time-sharing strategy, and we
introduce a measure to determine this improvement.Comment: 27 pages, 6 figures, some slight refinements and submitted to
Physical Review
Unconstrained Capacities of Quantum Key Distribution and Entanglement Distillation for Pure-Loss Bosonic Broadcast Channels
We consider quantum key distribution (QKD) and entanglement distribution
using a single-sender multiple-receiver pure-loss bosonic broadcast channel. We
determine the unconstrained capacity region for the distillation of bipartite
entanglement and secret key between the sender and each receiver, whenever they
are allowed arbitrary public classical communication. A practical implication
of our result is that the capacity region demonstrated drastically improves
upon rates achievable using a naive time-sharing strategy, which has been
employed in previously demonstrated network QKD systems. We show a simple
example of the broadcast QKD protocol overcoming the limit of the
point-to-point strategy. Our result is thus an important step toward opening a
new framework of network channel-based quantum communication technology.Comment: 9 pages, 5 figure
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