Vol.3 No.1 January 1,
2003
Researches:
Between entropy and subentropy
(pp114)
S.R. Nichols and
W.K. Wootters
The von Neumann entropy and the subentropy of a mixed
quantum state are upper and lower bounds, respectively, on the
accessible information of any ensemble consistent with the given mixed
state. Here we define and investigate a set of quantities intermediate
between entropy and subentropy.
Simulation of
quantum dynamics with quantum optical systems
(pp1537)
E. Jané, G. Vidal, W. Dür, P.
Zoller, J.I. Cirac
We propose the use of quantum optical systems to perform
universal simulation of quantum dynamics. Two specific implementations
that require present technology are put forward for illustrative
purposes. The first scheme consists of neutral atoms stored in optical
lattices, while the second scheme consists of ions stored in an array of
microtraps. Each atom (ion) supports a twolevel system, on which
local unitary operations can be performed through a laser beam. A raw
interaction between neighboring twolevel systems is achieved by
conditionally displacing the corresponding atoms (ions) Then, average
Hamiltonian techniques are used to achieve evolutions in time according
to a large class of Hamiltonians.
Dynamics of
distillability
(pp3847)
W. Wu, W. Wang, and
X. X. Yi
The time evolution of a maximally entangled bipartite
systems is presented in this paper. The distillability criterion is
given in terms of Kraus operators. Using the criterion, we discuss the
distillability of 2x2 and nxn (n>2) systems in their evolution process.
There are two distinguished processes, dissipation and decoherence,
which may destroy the distillability. We discuss the effects of those
processes on distillability in details.
On the problem
of authentication in a quantum protocol to detect traffic analysis
(pp4854)
J. MullerQuade and
R. Steinwandt
Recently, a basic design for a quantum protocol to detect
a perpetual traffic analysis of a communication channel has been
proposed\cite{SJB01}. As it stands, this protocol does not take the
problem of authentication into account. We show that a `standard'
authentication procedure does not apply in this context, as the attacker
is only interested in the number of transmitted bits. Moreover, we
demonstrate how to use a onetime pad like construction for solving this
authentication problem.
On the structure
of a reversible entanglement generating set for tripartite states
(pp5563)
A. Acin, G. Vidal
and J.I. Cirac
We show that EinsteinPodolskyRosenBohm (EPR) and
GreenbergerHorneZeilingerMermin (GHZ) states can not generate,
through local manipulation and in the asymptotic limit, all forms of
tripartite purestate entanglement in a reversible way. The techniques
that we use indicate that there is a connection between this result and
the irreversibility that occurs in the asymptotic preparation and
distillation of bipartite mixed states.
Local vs. joint
measurements for the entanglement of assistance
(pp6483)
T.
Laustsen, F. Verstraete, and S. J. van Enk We
consider a variant of the entanglement of assistance, as independently
introduced by D.P. DiVincenzo et al. (quantph/9803033) and O.
Cohen (Phys. Rev. Lett. 80, 2493 (1998)). Instead of considering
threeparty states in which one of the parties, the assistant, performs
a measurement such that the remaining two parties are left with on
average as much entanglement as possible, we consider fourparty states
where two parties play the role of assistants. We answer several
questions that arise naturally in this scenario, such as (i) how much
more entanglement can be produced when the assistants are allowed to
perform joint measurements, (ii) for what type of states are local
measurements sufficient, (iii) is it necessary for the second assistant
to know the measurement outcome of the first, and (iv) are projective
measurements sufficient or are more general POVMs needed?
Both Toffoli and ControlledNOT need
little help to universal quantum computing
(pp8492)
YY Shi
What additional gates are needed for a
set of classical universal gates to do universal quantum
computation? We prove that any
singlequbit real gate suffices, except those that preserve the
computational basis. The GottesmanKnill Theorem implies that any
quantum circuit involving only the ControlledNOT and Hadamard gates can
be efficiently simulated by a classical circuit. In contrast, we prove
that ControlledNOT plus any singlequbit real gate that does not
preserve the computational basis and is not Hadamard (or its like) are
universal for quantum computing. Previously only a generic gate, namely
a rotation by an angle incommensurate with \pi, is known to be
sufficient in both problems, if only one singlequbit gate is
added.
Book Review:
On “An Introduction to Quantum
Computing Algorithms” by A.O. Pittenger, “Quantum Computing” by M.
Hirvensalo, and "Classical and Quantum Computation” by A. Yu. Kitaev, A.
Shen, and M.N. Vyalyi
(pp9396)
R. de Wolf
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