8,151 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
Electron-radiation interaction in a Penning trap: beyond the dipole approximation
We investigate the physics of a single trapped electron interacting with a
radiation field without the dipole approximation. This gives new physical
insights in the so-called geonium theory.Comment: 12 pages, RevTeX, 6 figures, Approved for publication in Phys. Rev.
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
Entangled light pulses from single cold atoms
The coherent interaction between a laser-driven single trapped atom and an
optical high-finesse resonator allows to produce entangled multi-photon light
pulses on demand. The mechanism is based on the mechanical effect of light. The
degree of entanglement can be controlled through the parameters of the laser
excitation. Experimental realization of the scheme is within reach of current
technology. A variation of the technique allows for controlled generation of
entangled subsequent pulses, with the atomic motion serving as intermediate
memory of the quantum state.Comment: 4 pages, 3 figures, revised version (new scheme for generation of
subsequent pairs of entangled pulses included). Accepted for publication in
Phys. Rev. Let
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
A tomographic approach to quantum nonlocality
We propose a tomographic approach to study quantum nonlocality in continuous
variable quantum systems. On one hand we derive a Bell-like inequality for
measured tomograms. On the other hand, we introduce pseudospin operators whose
statistics can be inferred from the data characterizing the reconstructed
state, thus giving the possibility to use standard Bell's inequalities.
Illuminating examples are also discussed.Comment: 12 pages, 6 figures, IOP style, to appear in the Special Issue of J
Opt.B connected with Wigner Centennial conference (references added and
updated
Memory effects in attenuation and amplification quantum processes
With increasing communication rates via quantum channels, memory effects
become unavoidable whenever the use rate of the channel is comparable to the
typical relaxation time of the channel environment. We introduce a model of a
bosonic memory channel, describing correlated noise effects in quantum-optical
processes via attenuating or amplifying media. To study such a channel model,
we make use of a proper set of collective field variables, which allows us to
unravel the memory effects, mapping the n-fold concatenation of the memory
channel to a unitarily equivalent, direct product of n single-mode bosonic
channels. We hence estimate the channel capacities by relying on known results
for the memoryless setting. Our findings show that the model is characterized
by two different regimes, in which the cross correlations induced by the noise
among different channel uses are either exponentially enhanced or exponentially
reduced.Comment: 10 pages, 7 figures, close to the published versio
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