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Conference on Information Sciences and Systems

On Multicast in Quantum Networks

Yaoyun Shi, Emina Soljanin

Published Mar 1, 2006• 37 citations
Publisher

Abstract

We consider quantum multicast networks in which quantum states generated by multiple sources have to be simultaneously delivered to multiple receivers. We demonstrate that in addition to the apparent similarity to the multicommodity flow problems, quantum networks, to a certain extent, behave as classical communication networks. In particular, we show that lossless compression of special multicast quantum states is possible and significantly reduces the edge capacity requirements of the multicast.

DOI
10.1109/ciss.2006.286589

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We consider quantum multicast networks in which quantum states generated by multiple sources have to be simultaneously delivered to multiple receivers. We demonstrate that in addition to the apparent similarity to the multicommodity flow problems, quantum networks, to a certain extent, behave as classical communication networks. In particular, we show that lossless compression of special multicast quantum states is possible and significantly reduces the edge capacity requirements of the multicast.
We study the problem of perfectly multicasting symmetric universal clones of unknown quantum states over quantum networks with free classical communication. We construct a protocol that multicasts symmetric universal clones of input states from multiple source nodes by extending the quantum network coding protocol proposed by Kobayashi et al. We further establish a sufficient condition for perfect multicast in the single-source setting. Specifically, we show that when a single copy of a qrq^rqr-dimensional input state is available at the source node, where qqq is a sufficiently large prime power, perfect multicast of the corresponding symmetric universal clone is achievable using a small amount of entanglement shared among the target nodes. This result holds for quantum networks represented by an undirected graph GGG, where each edge corresponds to a noiseless qqq-dimensional quantum channel, provided that there exists an acyclic directed graph G′G'G′ obtained by assigning directions to the edges of GGG such that the minimum cut of G′G'G′ is at least rrr.
Abstract Quantum and private communications are affected by a fundamental limitation which severely restricts the optimal rates that are achievable by two distant parties. To overcome this problem, one needs to introduce quantum repeaters and, more generally, quantum communication networks. Within a quantum network, other problems and features may appear when we move from the basic unicast setting of single-sender/single-receiver to more complex multiend scenarios, where multiple senders and multiple receivers simultaneously use the network to communicate. Assuming various configurations, including multiple-unicast, multicast, and multiple-multicast communication, we bound the optimal rates for transmitting quantum information, distributing entanglement, or generating secret keys in quantum networks connected by arbitrary quantum channels. These bounds cannot be surpassed by the most general adaptive protocols of quantum network communication.
Multicast of unknown quantum states is an unavoidable issue in the construction of quantum networks. Most existing quantum network coding schemes can only restore an unknown state at one of the target nodes during multicast. In this paper, we propose a quantum network coding scheme to multicast unknown quantum states in networks with linear network coding. Concretely, GHZ states are generated between each sender and all receivers. Unknown states are then sent and stored in the entangled state shared by the receivers. Finally, the receivers use asymmetric optimal universal cloning to obtain the required states. The scheme achieved to multicast within 1 quantum transmission and 2 classical transmissions in networks with constrained classical communication. Compared to other schemes, our scheme allows receivers to autonomously adjust the fidelity without the sender knowing the requirements.
Multicasting of quantum states is an essential feature of quantum internet. Since the noncloning theorem prohibits perfect cloning of an unknown quantum state, an appropriate protocol may depend on the purpose of the multicast. In this paper, we treat the multicasting of a single copy of an unknown state over a quantum network with free classical communication. We especially focus on protocols exactly multicasting an asymmetric optimal universal clone. Hence, these protocols are optimal and universal in terms of mean fidelity between input and output states, but the fidelities can depend on target nodes. Among these protocols, a protocol spending smaller communication resources is preferable. Here, we construct such a protocol attaining the min-cut of the network described as follows. Two (three) asymmetric optimal clones of an input state are created at a source node. Then, the state is divided into classical information and a compressed quantum state. The state is sent to two (three) target nodes using the quantum network coding. Finally, the asymmetric clones are reconstructed using LOCC with a small amount of entanglement shared among the target nodes and the classical information sent from the source node.
This paper considers a problem of quantum communication between parties that are connected through a network of quantum channels. The model in this paper assumes that there is no prior entanglement shared among any of the parties, but that classical communication is free. The task is to perfectly transfer an unknown quantum state from a source subsystem to a target subsystem, where both source and target are formed by ordered sets of some of the nodes. It is proved that a lower bound of the rate at which this quantum communication task is possible is given by the classical min-cut max-flow theorem of network coding, where the capacities in question are the quantum capacities of the edges of the network.
This paper considers the problem of efficiently transmitting quantum states through a network. It has been known for some time that without additional assumptions it is impossible to achieve this task perfectly in general — indeed, it is impossible even for the simple butterfly network. As additional resource we allow free classical communication between any pair of network nodes. It is shown that perfect quantum network coding is achievable in this model whenever classical network coding is possible over the same network when replacing all quantum capacities by classical capacities. More precisely, it is proved that perfect quantum network coding using free classical communication is possible over a network with k source-target pairs if there exists a classical linear (or even vector-linear) coding scheme over a finite ring. Our proof is constructive in that we give explicit quantum coding operations for each network node. This paper also gives an upper bound on the number of classical communication required in terms of k, the maximal fan-in of any network node, and the size of the network. x1 x2 s1 ♠ s2 ♠ ❍❍❍❍ ❥ x1 x2 ✟ n1 x1 x1 ⊕ x2 x2 n2 ♠ x1 ⊕ x2✟ ❍❍❍❍ ❥ x1 ⊕ x2