Quantum computation and quantum information
Quantum computation and quantum information
Dense quantum coding and quantum finite automata
Journal of the ACM (JACM)
Improved Quantum Communication Complexity Bounds for Disjointness and Equality
STACS '02 Proceedings of the 19th Annual Symposium on Theoretical Aspects of Computer Science
Optimal Lower Bounds for Quantum Automata and Random Access Codes
FOCS '99 Proceedings of the 40th Annual Symposium on Foundations of Computer Science
Improved lower bounds for locally decodable codes and private information retrieval
ICALP'05 Proceedings of the 32nd international conference on Automata, Languages and Programming
IEEE Transactions on Information Theory
Foundations and Trends® in Networking
General Scheme for Perfect Quantum Network Coding with Free Classical Communication
ICALP '09 Proceedings of the 36th International Colloquium on Automata, Languages and Programming: Part I
A father protocol for quantum broadcast channels
IEEE Transactions on Information Theory
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Since quantum information is continuous, its handling is sometimes surprisingly harder than the classical counterpart. A typical example is cloning; making a copy of digital information is straightforward but it is not possible exactly for quantum information. The question in this paper is whether or not quantum network coding is possible. Its classical counterpart is another good example to show that digital information flow can be done much more efficiently than conventional (say, liquid) flow. Our answer to the question is similar to the case of cloning, namely, it is shown that quantum network coding is possible if approximation is allowed, by using a simple network model called Butterfly. In this network, there are two flow paths, s1 to t1 and s2 to t2, which shares a single bottleneck channel of capacity one. In the classical case, we can send two bits simultaneously, one for each path, in spite of the bottleneck. Our results for quantum network coding include: (i) We can send any quantum state |ψ1〉 from s1 to t1 and |ψ2〉 from s2 to t2 simultaneously with a fidelity strictly greater than 1/2. (ii) If one of |ψ1〉 and |ψ2〉 is classical, then the fidelity can be improved to 2/3. (iii) Similar improvement is also possible if |ψ1〉 and |ψ2〉 are restricted to only a finite number of (previously known) states. (iv) Several impossibility results including the general upper bound of the fidelity are also given.