98 research outputs found
Quantum broadcast channels
We consider quantum channels with one sender and two receivers, used in
several different ways for the simultaneous transmission of independent
messages. We begin by extending the technique of superposition coding to
quantum channels with a classical input to give a general achievable region. We
also give outer bounds to the capacity regions for various special cases from
the classical literature and prove that superposition coding is optimal for a
class of channels. We then consider extensions of superposition coding for
channels with a quantum input, where some of the messages transmitted are
quantum instead of classical, in the sense that the parties establish bipartite
or tripartite GHZ entanglement. We conclude by using state merging to give
achievable rates for establishing bipartite entanglement between different
pairs of parties with the assistance of free classical communication.Comment: 15 pages; IEEE Trans. Inform. Theory, vol. 57, no. 10, October 201
A father protocol for quantum broadcast channels
A new protocol for quantum broadcast channels based on the fully quantum
Slepian-Wolf protocol is presented. The protocol yields an achievable rate
region for entanglement-assisted transmission of quantum information through a
quantum broadcast channel that can be considered the quantum analogue of
Marton's region for classical broadcast channels. The protocol can be adapted
to yield achievable rate regions for unassisted quantum communication and for
entanglement-assisted classical communication; in the case of unassisted
transmission, the region we obtain has no independent constraint on the sum
rate, only on the individual transmission rates. Regularized versions of all
three rate regions are provably optimal.Comment: Typo in statement of Theorem 4 fixe
Hadamard quantum broadcast channels
We consider three different communication tasks for quantum broadcast channels, and we determine the capacity region of a Hadamard broadcast channel for these various tasks. We define a Hadamard broadcast channel to be such that the channel from the sender to one of the receivers is entanglement-breaking and the channel from the sender to the other receiver is complementary to this one. As such, this channel is a quantum generalization of a degraded broadcast channel, which is well known in classical information theory. The first communication task we consider is classical communication to both receivers, the second is quantum communication to the stronger receiver and classical communication to other, and the third is entanglement-assisted classical communication to the stronger receiver and unassisted classical communication to the other. The structure of a Hadamard broadcast channel plays a critical role in our analysis: The channel to the weaker receiver can be simulated by performing a measurement channel on the stronger receiver’s system, followed by a preparation channel. As such, we can incorporate the classical output of the measurement channel as an auxiliary variable and solve all three of the above capacities for Hadamard broadcast channels, in this way avoiding known difficulties associated with quantum auxiliary variables
Classical codes for quantum broadcast channels
We present two approaches for transmitting classical information over quantum
broadcast channels. The first technique is a quantum generalization of the
superposition coding scheme for the classical broadcast channel. We use a
quantum simultaneous nonunique decoder and obtain a proof of the rate region
stated in [Yard et al., IEEE Trans. Inf. Theory 57 (10), 2011]. Our second
result is a quantum generalization of the Marton coding scheme. The error
analysis for the quantum Marton region makes use of ideas in our earlier work
and an idea recently presented by Radhakrishnan et al. in arXiv:1410.3248. Both
results exploit recent advances in quantum simultaneous decoding developed in
the context of quantum interference channels.Comment: v4: 20 pages, final version to appear in IEEE Transactions on
Information Theor
Classical codes for quantum broadcast channels
We discuss two techniques for transmitting classical information over quantum broadcast channels. The first technique is a quantum generalization of the superposition coding scheme for the classical broadcast channel. We use a quantum simultaneous nonunique decoder and obtain a simpler proof of the rate region recently published by Yard et al. in independent work. Our second result is a quantum Marton coding scheme, which gives the best known achievable rate region for quantum broadcast channels. Both results exploit recent advances in quantum simultaneous decoding developed in the context of quantum interference channels. © 2012 IEEE
An improved rate region for the classical-quantum broadcast channel
We present a new achievable rate region for the two-user binary-input
classical-quantum broadcast channel. The result is a generalization of the
classical Marton-Gelfand-Pinsker region and is provably larger than the best
previously known rate region for classical-quantum broadcast channels. The
proof of achievability is based on the recently introduced polar coding scheme
and its generalization to quantum network information theory.Comment: 5 pages, double column, 1 figure, based on a result presented in the
Master's thesis arXiv:1501.0373
Bounds on entanglement distillation and secret key agreement for quantum broadcast channels
The squashed entanglement of a quantum channel is an additive function of
quantum channels, which finds application as an upper bound on the rate at
which secret key and entanglement can be generated when using a quantum channel
a large number of times in addition to unlimited classical communication. This
quantity has led to an upper bound of on the capacity
of a pure-loss bosonic channel for such a task, where is the average
fraction of photons that make it from the input to the output of the channel.
The purpose of the present paper is to extend these results beyond the
single-sender single-receiver setting to the more general case of a single
sender and multiple receivers (a quantum broadcast channel). We employ
multipartite generalizations of the squashed entanglement to constrain the
rates at which secret key and entanglement can be generated between any subset
of the users of such a channel, along the way developing several new properties
of these measures. We apply our results to the case of a pure-loss broadcast
channel with one sender and two receivers.Comment: 35 pages, 1 figure, accepted for publication in IEEE Transactions on
Information Theor
Entanglement-assisted private communication over quantum broadcast channels
We consider entanglement-assisted (EA) private communication over a quantum
broadcast channel, in which there is a single sender and multiple receivers. We
divide the receivers into two sets: the decoding set and the malicious set. The
decoding set and the malicious set can either be disjoint or can have a finite
intersection. For simplicity, we say that a single party Bob has access to the
decoding set and another party Eve has access to the malicious set, and both
Eve and Bob have access to the pre-shared entanglement with Alice. The goal of
the task is for Alice to communicate classical information reliably to Bob and
securely against Eve, and Bob can take advantage of pre-shared entanglement
with Alice. In this framework, we establish a lower bound on the one-shot EA
private capacity. When there exists a quantum channel mapping the state of the
decoding set to the state of the malicious set, such a broadcast channel is
said to be degraded. We establish an upper bound on the one-shot EA private
capacity in terms of smoothed min- and max-entropies for such channels. In the
limit of a large number of independent channel uses, we prove that the EA
private capacity of a degraded quantum broadcast channel is given by a
single-letter formula. Finally, we consider two specific examples of degraded
broadcast channels and find their capacities. In the first example, we consider
the scenario in which one part of Bob's laboratory is compromised by Eve. We
show that the capacity for this protocol is given by the conditional quantum
mutual information of a quantum broadcast channel, and so we thus provide an
operational interpretation to the dynamic counterpart of the conditional
quantum mutual information. In the second example, Eve and Bob have access to
mutually exclusive sets of outputs of a broadcast channel.Comment: v2: 23 pages, 2 figures, accepted for publication in the special
issue "Shannon's Information Theory 70 years on: applications in classical
and quantum physics" for Journal of Physics
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