187 research outputs found
Informationally complete measurements and groups representation
Informationally complete measurements on a quantum system allow to estimate
the expectation value of any arbitrary operator by just averaging functions of
the experimental outcomes. We show that such kind of measurements can be
achieved through positive-operator valued measures (POVM's) related to unitary
irreducible representations of a group on the Hilbert space of the system. With
the help of frame theory we provide a constructive way to evaluate the
data-processing function for arbitrary operators.Comment: 9 pages, no figures, IOP style. Some new references adde
Approaching the Heisenberg limit with two mode squeezed states
Two mode squeezed states can be used to achieve Heisenberg limit scaling in
interferometry: a phase shift of can be
resolved. The proposed scheme relies on balanced homodyne detection and can be
implemented with current technology. The most important experimental
imperfections are studied and their impact quantified.Comment: 4 pages, 7 figure
Quantum reconstruction of an intense polarization squeezed optical state
We perform a reconstruction of the polarization sector of the density matrix
of an intense polarization squeezed beam starting from a complete set of Stokes
measurements. By using an appropriate quasidistribution, we map this onto the
Poincare space providing a full quantum mechanical characterization of the
measured polarization state.Comment: 4 pages, 4 eps color figure
Schrodinger cats and their power for quantum information processing
We outline a toolbox comprised of passive optical elements, single photon
detection and superpositions of coherent states (Schrodinger cat states). Such
a toolbox is a powerful collection of primitives for quantum information
processing tasks. We illustrate its use by outlining a proposal for universal
quantum computation. We utilize this toolbox for quantum metrology
applications, for instance weak force measurements and precise phase
estimation. We show in both these cases that a sensitivity at the Heisenberg
limit is achievable.Comment: 10 pages, 5 figures; Submitted to a Special Issue of J. Opt. B on
"Fluctuations and Noise in Photonics and Quantum Optics" (Herman Haus
Memorial Issue
Avvio e gestione di attivitĂ estrattive: un approccio in "Prevention Through Design"
Una efficace analisi e gestione dei rischi presso le unitĂ estrattive, su cui fondare lâattivitĂ in coerenza con le norme vigenti in materia di sicurezza del lavoro, implica un approccio pro-attivo, tenuto conto dei diversi fattori coinvolti.
In tale contesto un approccio pro-attivo richiede una approfondita analisi di rischio, fondata sulla valutazione delle possibili opzioni progettuali e la conoscenza del sito e del programma di coltivazione; nel presente lavoro viene esposta una metodologia basata su un sistema di registrazione dei dati tecnici supportata da un apposito software interattivo, in grado di aiutare la valutazione degli aspetti generali e specifici della sicurezza di comparto e di singole unitĂ estrattive.
Il lavoro Ăš stato svolto dal Dipartimento di Ingegneria del Territorio, dellâAmbiente e delle Geotecnologie del Politecnico di Torino (giĂ Autore di Linee Guida in materia di sicurezza per il comparto estrattivo) con il supporto dellâUfficio Tutela Ambientale della Provincia di Torino
Entanglement purification of multi-mode quantum states
An iterative random procedure is considered allowing an entanglement
purification of a class of multi-mode quantum states. In certain cases, a
complete purification may be achieved using only a single signal state
preparation. A physical implementation based on beam splitter arrays and
non-linear elements is suggested. The influence of loss is analyzed in the
example of a purification of entangled N-mode coherent states.Comment: 6 pages, 3 eps-figures, using revtex
Binary optical communication in single-mode and entangled quantum noisy channels
We address binary optical communication in single-mode and entangled quantum
noisy channels. For single-mode we present a systematic comparison between
direct photodetection and homodyne detection in realistic conditions, i.e.
taking into account the noise that occurs both during the propagation and the
detection of the signals. We then consider entangled channels based on
twin-beam state of radiation, and show that with realistic heterodyne detection
the error probability at fixed channel energy is reduced in comparison to the
single-mode cases for a large range of values of quantum efficiency and noise
parameters
Iterative algorithm for reconstruction of entangled states
An iterative algorithm for the reconstruction of an unknown quantum state
from the results of incompatible measurements is proposed. It consists of
Expectation-Maximization step followed by a unitary transformation of the
eigenbasis of the density matrix. The procedure has been applied to the
reconstruction of the entangled pair of photons.Comment: 4 pages, no figures, some formulations changed, a minor mistake
correcte
Iterative maximum-likelihood reconstruction in quantum homodyne tomography
I propose an iterative expectation maximization algorithm for reconstructing
a quantum optical ensemble from a set of balanced homodyne measurements
performed on an optical state. The algorithm applies directly to the acquired
data, bypassing the intermediate step of calculating marginal distributions.
The advantages of the new method are made manifest by comparing it with the
traditional inverse Radon transformation technique
Exchange Gate on the Qudit Space and Fock Space
We construct the exchange gate with small elementary gates on the space of
qudits, which consist of three controlled shift gates and three "reverse"
gates. This is a natural extension of the qubit case.
We also consider a similar subject on the Fock space, but in this case we
meet with some different situation. However we can construct the exchange gate
by making use of generalized coherent operator based on the Lie algebra su(2)
which is a well--known method in Quantum Optics. We moreover make a brief
comment on "imperfect clone".Comment: Latex File, 12 pages. I could solve the problems in Sec. 3 in the
preceding manuscript, so many corrections including the title were mad
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