6,874 research outputs found
Reconstructing the density operator by using generalized field quadratures
The Wigner function for one and two-mode quantum systems is explicitely
expressed in terms of the marginal distribution for the generic linearly
transformed quadratures. Then, also the density operator of those systems is
written in terms of the marginal distribution of these quadratures. Some
examples to apply this formalism, and a reduction to the usual optical homodyne
tomography are considered.Comment: 17 pages, Latex,accepted by Quantum and Semiclassical Optic
Density Matrix From Photon Number Tomography
We provide a simple analytic relation which connects the density operator of
the radiation field with the number probabilities. The problem of
experimentally "sampling" a general matrix elements is studied, and the
deleterious effects of nonunit quantum efficiency in the detection process are
analyzed showing how they can be reduced by using the squeezing technique. The
obtained result is particulary useful for intracavity field reconstruction
states.Comment: LATEX,6 pages,accepted by Europhysics Letter
Beyond the Standard "Marginalizations" of Wigner Function
We discuss the problem of finding "marginal" distributions within different
tomographic approaches to quantum state measurement, and we establish
analytical connections among them.Comment: 12 pages, LaTex, no figures, to appear in Quantum and Semiclass. Op
Deformed versus undeformed cat states encoding qubit
We study the possibility of exploiting superpositions of coherent states to
encode qubit. A comparison between the use of deformed and undeformed bosonic
algebra is made in connection with the amplitude damping errors.Comment: 6 pages, 2 eps figures, to appear in J. Opt.
The Pauli Equation for Probability Distributions
The "marginal" distributions for measurable coordinate and spin projection is
introduced. Then, the analog of the Pauli equation for spin-1/2 particle is
obtained for such probability distributions instead of the usual wave
functions. That allows a classical-like approach to quantum mechanics. Some
illuminating examples are presented.Comment: 14 pages, ReVTe
Permutation symmetry for the tomographic probability distribution of a system of identical particles
The symmetry properties under permutation of tomograms representing the
states of a system of identical particles are studied. Starting from the action
of the permutation group on the density matrix we define its action on the
tomographic probability distribution. Explicit calculations are performed in
the case of the two-dimensional harmonic oscillator.Comment: 13 pages, latex, no figure
Synthesis and characterization of entangled mesoscopic superpositions for a trapped electron
We propose a scheme for the generation and reconstruction of entangled states
between the internal and external (motional) degrees of freedom of a trapped
electron. Such states also exhibit quantum coherence at a mesoscopic level.Comment: 4 pages, 1 figure, RevTeX (twocolumn
Back-action cancellation in interferometers by quantum locking
We show that back-action noise in interferometric measurements such as
gravitational-waves detectors can be completely suppressed by a local control
of mirrors motion. An optomechanical sensor with an optimized measurement
strategy is used to monitor mirror displacements. A feedback loop then
eliminates radiation-pressure effects without adding noise. This very efficient
technique leads to an increased sensitivity for the interferometric
measurement, which becomes only limited by phase noise. Back-action
cancellation is furthermore insensitive to losses in the interferometer.Comment: 4 pages, 3 figures, RevTe
Quantum Characterization of a Werner-like Mixture
We introduce a Werner-like mixture [R. F. Werner, Phys. Rev. A {\bf 40}, 4277
(1989)] by considering two correlated but different degrees of freedom, one
with discrete variables and the other with continuous variables. We evaluate
the mixedness of this state, and its degree of entanglement establishing its
usefulness for quantum information processing like quantum teleportation. Then,
we provide its tomographic characterization. Finally, we show how such a
mixture can be generated and measured in a trapped system like one electron in
a Penning trap.Comment: 8 pages ReVTeX, 8 eps figure
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