1,906 research outputs found
Recent Developments in Parallelization of the Multidimensional Integration Package DICE
DICE is a general purpose multidimensional numerical integration package.
There can be two ways in the parallelization of DICE, "distributing random
numbers into workers" and "distributing hypercubes into workers". Furthermore,
there can be the combination of both ways. So far, we had developed the
parallelization code using the former way and reported it in ACAT2002 in
Moscow. Here, we will present the recent developments of parallelized DICE in
the latter way as the 2nd stage of our parallelization activities.Comment: 5 pages, 2 figures, Talk given at the X International Workshop on
Advanced Computing and Analysis Techniques in Physics Research, ACAT 2005,
DESY-Zeuthen, Germany, 22-27 May 200
Oscillations of the purity in the repeated-measurement-based generation of quantum states
Repeated observations of a quantum system interacting with another one can
drive the latter toward a particular quantum state, irrespectively of its
initial condition, because of an {\em effective non-unitary evolution}. If the
target state is a pure one, the degree of purity of the system approaches
unity, even when the initial condition of the system is a mixed state. In this
paper we study the behavior of the purity from the initial value to the final
one, that is unity. Depending on the parameters, after a finite number of
measurements, the purity exhibits oscillations, that brings about a lower
purity than that of the initial state, which is a point to be taken care of in
concrete applications.Comment: 5 pages, 3 figure
Selective writing and read-out of a register of static qubits
We propose a setup comprising an arbitrarily large array of static qubits
(SQs), which interact with a flying qubit (FQ). The SQs work as a quantum
register, which can be written or read-out by means of the FQ through quantum
state transfer (QST). The entire system, including the FQ's motional degrees of
freedom, behaves quantum mechanically. We demonstrate a strategy allowing for
selective QST between the FQ and a single SQ chosen from the register. This is
achieved through a perfect mirror located beyond the SQs and suitable
modulation of the inter-SQ distances.Comment: 14 pages, 4 figure
Extraction of an Entanglement by Repetition of the Resonant Transmission of an Ancilla Qubit
A scheme for the extraction of entanglement in two noninteracting qubits
(spins) is proposed. The idea is to make use of resonant transmission of
ancilla qubit through the two fixed qubits, controlled by the entanglement in
the scatterers. Repetition of the resonant transmission extracts the singlet
state in the target qubits from their arbitrary given state. Neither the
preparation nor the post-selection of the ancilla spin is required, in contrast
to the previously proposed schemes.Comment: 14 pages, 7 figure
Entanglement Purification through Zeno-like Measurements
We present a novel method to purify quantum states, i.e. purification through
Zeno-like measurements, and show an application to entanglement purification.Comment: 5 pages, 1 figure; Contribution to the Proceedings of "Mysteries,
Puzzles and Paradoxes in Quantum Mechanics", Gargnano, Italy, 2003 (to be
published in J. Mod. Opt.
Entanglement-assisted tomography of a quantum target
We study the efficiency of quantum tomographic reconstruction where the
system under investigation (quantum target) is indirectly monitored by looking
at the state of a quantum probe that has been scattered off the target. In
particular we focus on the state tomography of a qubit through a
one-dimensional scattering of a probe qubit, with a Heisenberg-type
interaction. Via direct evaluation of the associated quantum Cram\'{e}r-Rao
bounds, we compare the accuracy efficiency that one can get by adopting
entanglement-assisted strategies with that achievable when entanglement
resources are not available. Even though sub-shot noise accuracy levels are not
attainable, we show that quantum correlations play a significant role in the
estimation. A comparison with the accuracy levels obtainable by direct
estimation (not through a probe) of the quantum target is also performed.Comment: 22 pages, 9 figure
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