QIC Abstracts

 Vol.1 No.3 Oct. 15, 2001 (in print: Nov. 15, 2001)
Bell inequalities and entanglement (pp1-25)
        R Werner & M Wolf
We discuss general Bell inequalities for bipartite and multipartite systems, emphasizing the connection with convex geometry on the mathematical side, and the communication aspects on the physical side. Known results on families of generalized Bell inequalities are summarized. We investigate maximal violations of Bell inequalities as well as states not violating (certain) Bell inequalities. Finally, we discuss the relation between Bell inequality violations and entanglement properties currently discussed in quantum information theory.

Decomposing finite Abelian groups (pp26-32)
        K Cheung & M Mosca

This paper describes a quantum algorithm for efficiently decomposing finite Abelian groups into a product of cyclic groups. Such a decomposition is needed in order to apply the Abelian hidden subgroup algorithm. Such a decomposition (assuming the Generalized Riemann Hypothesis) also leads to an efficient algorithm for computing class numbers (known to be at least as difficult as factoring).

Optimal two-particle entanglement by universal quantum processes (pp33-51)
        G Alber, A Delgado & I Jex
Within the class of all possible universal (covariant) two-particle quantum processes in arbitrary dimensional Hilbert spaces those universal quantum processes are determined whose output states optimize the recently proposed entanglement measure of Vidal and Werner. It is demonstrated that these optimal entanglement processes belong to a one-parameter family of universal entanglement processes whose output states do not contain any separable components. It is shown that these optimal universal entanglement processes generate antisymmetric output states and, with the single exception of qubit systems, they preserve information about the initial input state.

Optimal quantum measurements for spin-1 and spin-3/2 particles  (pp52-61)
        P Aravind
Positive operator valued measures (POVMs) are presented that allow an unknown pure state of a spin-1 particle to be determined with optimal fidelity when 2 to 5 copies of that state are available. Optimal POVMs are also presented for a spin-3/2 particle when 2 or 3 copies of the unknown state are available. Although these POVMs are optimal they are not always minimal, indicating that there is room for improvement.

On using quantum protocols to detect traffic analysis (pp62-69)
        R Steinwandt, D Janzing & T Beth
We consider the problem of detecting whether an attacker measures the amount of traffic sent over a communication channel--possibly without extracting information about the transmitted data. A basic approach for designing a quantum protocol for detecting a perpetual traffic analysis of this kind is described.

Classical capacity of a noiseless quantum channel assisted by noisy entanglement  (pp70-78)
        M Horodecki, P Horodecki, R Horodecki, D Leung & B Terhal
We derive the general formula for the capacity of a noiseless quantum channel assisted by an arbitrary amount of noisy entanglement. In this capacity formula, the ratio of the quantum mutual information and the von Neumann entropy of the sender's share of the noisy entanglement plays the role of mutual information in the completely classical case. A consequence of our results is that bound entangled states cannot increase the capacity of a noiseless quantum channel.

Distillability criterion for all bipartite Gaussian states (pp79-86)
        G Giedke, L-M Duan, I Cirac & P Zoller
We prove that all inseparable Gaussian states of two modes can be distilled into maximally entangled pure states by local operations. Using this result we show that a bipartite Gaussian state of arbitrarily many modes can be distilled if and only if its partial transpose is not positive.

Long-distance quantum communication just around the corner?   (pp87-88)
        P Kok, H Lee, N Cerf & J Dowling

Book review:
on “The Physics of Quantum Information: Quantum Cryptography, Quantum Teleportation, Quantum Computation" (edited by D Bouwmeester, A Ekert & A Zeilinger)  (pp89-90)
        G Milburn
update (pp91-92)
        P Kok

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