967 research outputs found
Quantum Capacities for Entanglement Networks
We discuss quantum capacities for two types of entanglement networks:
for the quantum repeater network with free classical
communication, and for the tensor network as the rank of the
linear operation represented by the tensor network. We find that
always equals in the regularized case for the samenetwork graph.
However, the relationships between the corresponding one-shot capacities
and are more complicated, and the min-cut upper
bound is in general not achievable. We show that the tensor network can be
viewed as a stochastic protocol with the quantum repeater network, such that
is a natural upper bound of . We analyze the
possible gap between and for certain networks,
and compare them with the one-shot classical capacity of the corresponding
classical network
Quantum network coding for quantum repeaters
This paper considers quantum network coding, which is a recent technique that
enables quantum information to be sent on complex networks at higher rates than
by using straightforward routing strategies. Kobayashi et al. have recently
showed the potential of this technique by demonstrating how any classical
network coding protocol gives rise to a quantum network coding protocol. They
nevertheless primarily focused on an abstract model, in which quantum resource
such as quantum registers can be freely introduced at each node. In this work,
we present a protocol for quantum network coding under weaker (and more
practical) assumptions: our new protocol works even for quantum networks where
adjacent nodes initially share one EPR-pair but cannot add any quantum
registers or send any quantum information. A typically example of networks
satisfying this assumption is {\emph{quantum repeater networks}}, which are
promising candidates for the implementation of large scale quantum networks.
Our results thus show, for the first time, that quantum network coding
techniques can increase the transmission rate in such quantum networks as well.Comment: 9 pages, 11figure
Topology Adaption for the Quantum Internet
In the quantum repeater networks of the quantum Internet, the varying
stability of entangled quantum links makes dynamic topology adaption an
emerging issue. Here we define an efficient topology adaption method for
quantum repeater networks. The model assumes the random failures of entangled
links and several parallel demands from legal users. The shortest path defines
a set of entangled links for which the probability of stability is above a
critical threshold. The scheme is utilized in a base-graph of the overlay
quantum network to provide an efficient shortest path selection for the demands
of all users of the network. We study the problem of entanglement assignment in
a quantum repeater network, prove its computational complexity, and show an
optimization procedure. The results are particularly convenient for future
quantum networking, quantum-Internet, and experimental long-distance quantum
communications.Comment: 17 pages, Journal-ref: Quant. Inf. Proc. (2018
Assisted Entanglement Distillation
Motivated by the problem of designing quantum repeaters, we study
entanglement distillation between two parties, Alice and Bob, starting from a
mixed state and with the help of "repeater" stations. To treat the case of a
single repeater, we extend the notion of entanglement of assistance to
arbitrary mixed tripartite states and exhibit a protocol, based on a random
coding strategy, for extracting pure entanglement. The rates achievable by this
protocol formally resemble those achievable if the repeater station could merge
its state to one of Alice and Bob even when such merging is impossible. This
rate is provably better than the hashing bound for sufficiently pure tripartite
states. We also compare our assisted distillation protocol to a hierarchical
strategy consisting of entanglement distillation followed by entanglement
swapping. We demonstrate by the use of a simple example that our random
measurement strategy outperforms hierarchical distillation strategies when the
individual helper stations' states fail to individually factorize into portions
associated specifically with Alice and Bob. Finally, we use these results to
find achievable rates for the more general scenario, where many spatially
separated repeaters help two recipients distill entanglement.Comment: 25 pages, 4 figure
- …