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).
two-particle entanglement by universal quantum processes
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
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
M Horodecki, P Horodecki, R Horodecki, D Leung & B
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
Distillability criterion for all
bipartite Gaussian states
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.
communication just around the corner?
P Kok, H Lee, N Cerf & J Dowling
on The Physics of
Quantum Information: Quantum Cryptography, Quantum Teleportation, Quantum Computation" (edited by D Bouwmeester, A Ekert & A Zeilinger)