Vol.2 No.4 June 15, 2002 (print: July 15,
2002)
Researches:
Transport of quantum states and
separation of ions in a dual RF ion trap
(pp257271)
M.A. Rowe, A. BenKish, B. DeMarco, D.
Leibfried, V. Meyer, J. Beall, J. Britton, J. Hughes, W.M. Itano, B.
Jelenkovic, C. Langer, T. Rosenband, and D.J. Wineland
We have investigated ion dynamics associated with a dual
linear ion trap where ions can be stored in and moved between two
distinct locations. Such a trap is a building block for a system to
engineer arbitrary quantum states of ion ensembles. Specifically, this
trap is the unit cell in a strategy for scalable quantum computing using
a series of interconnected ion traps. We have transferred an ion between
trap locations 1.2 mm apart in 50 $\mu$s with near unit efficiency ($>
10^{6}$ consecutive transfers) and negligible motional heating, while
maintaining internalstate coherence. In addition, we have separated two
ions held in a common trap into two distinct traps.
Quantum
statistical properties in a single trapped ion interacting with a laser
fields
(pp272284)
M. AbdelAty, S. Furuichi, and S. Nakamura
In this paper
we use the quasimutual entropy, which does not depend on quantum
channel, as a measure of information content of ionic state due to
ionlaser interaction in a single trapped ion. It is found that the
quasimutual entropy is a good measure of the entanglement degree of the
ionic state at any time. We examine numerically the population
inversion, the photon number distribution and degree of entanglement due
to quasimutual entropy for a single trapped ion interacting with a
laser field. During the transition from collapse to revival and
viceversa we have a minimum degree of entanglement value. Successive
revival peaks show a lowering of the local maximum points indicating a
dissipative irreversible change in the ionic state. We propose a
generation of Belltype states having a simple initial state preparation
of a single trapped ion. Timeoptimal
Hamiltonian simulation and gate synthesis using homogeneous local
unitaries
(pp285296)
Ll. Masanes, G. Vidal, and J.I. Latorre
Motivated by experimental limitations commonly met in the
design of solid state quantum computers, we study the problems of
nonlocal Hamiltonian simulation and nonlocal gate synthesis when
only {\em homogeneous} local unitaries are performed in order to tailor
the available interaction. Homogeneous (i.e. identical for all
subsystems) local manipulation implies a more refined classification of
interaction Hamiltonians than the inhomogeneous case, as well as the
loss of universality in Hamiltonian simulation. For the case of
symmetric twoqubit interactions, we provide timeoptimal protocols
for both Hamiltonian simulation and gate synthesis. Quantum computer
architecture for fast entropy extraction
(pp297306)
A.M. Steane
If a quantum computer is
stabilized by faulttolerant quantum error correction (QEC), then most
of its resources (qubits and operations) are dedicated to the extraction
of error information. Analysis of this process leads to a set of central
requirements for candidate computing devices, in addition to the basic
ones of stable qubits and controllable gates and measurements. The
logical structure of the extraction process has a natural geometry and
hierarchy of communication needs; a computer whose physical architecture
is designed to reflect this will be able to tolerate the most noise. The
relevant networks are dominated by quantum information transport,
therefore to assess a computing device it is necessary to characterize
its ability to transport quantum information, in addition to assessing
the performance of conditional logic on nearest neighbours and the
passive stability of the memory. The transport distances involved in QEC
networks are estimated, and it is found that a device relying on swap
operations for information transport must have those operations an order
of magnitude more precise than the controlled gates of a device which
can transport information at low cost. Stabilizer codes
can be realized as graph codes
(pp307323)
D Schlingemann
We establish the
connection between a recent new construction technique for quantum
error correcting codes, based on graphs, and the socalled stabilizer
codes: Each stabilizer code can be realized as a graph code and vice
versa. ROMbased
computation: quantum versus classical
(pp324332)
B.C. Travaglione, M.A. Nielsen, H.M. Wiseman and A. Ambainis
We introduce a model of computation
based on \emph{read only memory} (ROM), which allows us to compare the
spaceefficiency of reversible, errorfree classical computation with
reversible, errorfree quantum computation. We show that a ROMbased
quantum computer with one writable qubit is universal, whilst two
writable bits are required for a universal classical ROMbased computer.
We also comment on the timeefficiency advantages of quantum computation
within this model.
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