98 research outputs found
Entangled-photon Fourier optics
Entangled photons, generated by spontaneous parametric down-conversion from a
second-order nonlinear crystal, present a rich potential for imaging and
image-processing applications. Since this source is an example of a three-wave
mixing process, there is more flexibility in the choices of illumination and
detection wavelengths and in the placement of object(s) to be imaged. Moreover,
this source is entangled, a fact that allows for imaging configurations and
capabilities that cannot be achieved using classical sources of light. In this
paper we examine a number of imaging and image-processing configurations that
can be realized using this source. The formalism that we utilize facilitates
the determination of the dependence of imaging resolution on the physical
parameters of the optical arrangement.Comment: 41 pages, 12 figures, accepted for publication in J. Opt. Soc. Am.
Role of entanglement in two-photon imaging
The use of entangled photons in an imaging system can exhibit effects that
cannot be mimicked by any other two-photon source, whatever the strength of the
correlations between the two photons. We consider a two-photon imaging system
in which one photon is used to probe a remote (transmissive or scattering)
object, while the other serves as a reference. We discuss the role of
entanglement versus correlation in such a setting, and demonstrate that
entanglement is a prerequisite for achieving distributed quantum imaging.Comment: 15 pages, 2 figure
Nano-displacement measurements using spatially multimode squeezed light
We demonstrate the possibility of surpassing the quantum noise limit for
simultaneous multi-axis spatial displacement measurements that have zero mean
values. The requisite resources for these measurements are squeezed light beams
with exotic transverse mode profiles. We show that, in principle, lossless
combination of these modes can be achieved using the non-degenerate Gouy phase
shift of optical resonators. When the combined squeezed beams are measured with
quadrant detectors, we experimentally demonstrate a simultaneous reduction in
the transverse x- and y- displacement fluctuations of 2.2 dB and 3.1 dB below
the quantum noise limit.Comment: 21 pages, 9 figures, submitted to "Special Issue on Fluctuations &
Noise in Photonics & Quantum Optics" of J. Opt.
Quantum state reconstruction of the single-photon Fock state
We have reconstructed the quantum state of optical pulses containing single
photons using the method of phase-randomized pulsed optical homodyne
tomography. The single-photon Fock state |1> was prepared using conditional
measurements on photon pairs born in the process of parametric down-conversion.
A probability distribution of the phase-averaged electric field amplitudes with
a strongly non-Gaussian shape is obtained with the total detection efficiency
of (55+-1)%. The angle-averaged Wigner function reconstructed from this
distribution shows a strong dip reaching classically impossible negative values
around the origin of the phase space.Comment: 4 pages, 4 figures, to appear in Physical Review Letters. Avoid
downloading PDF due to extremely poor figure resolution. Use Postscrip
Multi-Parameter Entanglement in Femtosecond Parametric Down-Conversion
A theory of spontaneous parametric down-conversion, which gives rise to a
quantum state that is entangled in multiple parameters, such as
three-dimensional wavevector and polarization, allows us to understand the
unusual characteristics of fourth-order quantum interference in many
experiments, including ultrafast type-II parametric down-conversion, the
specific example illustrated in this paper. The comprehensive approach provided
here permits the engineering of quantum states suitable for quantum information
schemes and new quantum technologies.Comment: to appear in Physical Review
Review of recent experimental progresses in Foundations of Quantum Mechanics and Quantum Information obtained in Parametric Down Conversion Experiments at IENGF
We review some recent experimental progresses concerning Foundations of
Quantum Mechanics and Quantum Information obtained in Quantum Optics Laboratory
"Carlo Novero" at IENGF.
More in details, after a short presentation of our polarization entangled
photons source (based on precise superposition of two Type I PDC emission) and
of the results obtained with it, we describe an innovative double slit
experiment where two degenerate photons produced by PDC are sent each to a
specific slit. Beyond representing an interesting example of relation between
visibility of interference and "welcher weg" knowledge, this configuration has
been suggested for testing de Broglie-Bohm theory against Standard Quantum
Mechanics. Our results perfectly fit SQM results, but disagree with dBB
predictions.
Then, we discuss a recent experiment addressed to clarify the issue of which
wave-particle observables are really to be considered when discussing wave
particle duality. This experiments realises the Agarwal et al. theoretical
proposal, overcoming limitations of a former experiment.
Finally, we hint to the realization of a high-intensity
high-spectral-selected PDC source to be used for quantum information studies
Multi-parameter Entanglement in Quantum Interferometry
The role of multi-parameter entanglement in quantum interference from
collinear type-II spontaneous parametric down-conversion is explored using a
variety of aperture shapes and sizes, in regimes of both ultrafast and
continuous-wave pumping. We have developed and experimentally verified a theory
of down-conversion which considers a quantum state that can be concurrently
entangled in frequency, wavevector, and polarization. In particular, we
demonstrate deviations from the familiar triangular interference dip, such as
asymmetry and peaking. These findings improve our capacity to control the
quantum state produced by spontaneous parametric down-conversion, and should
prove useful to those pursuing the many proposed applications of down-converted
light.Comment: submitted to Physical Review
Surpassing the standard quantum limit for optical imaging using nonclassical multimode light
Using continuous wave superposition of spatial modes, we demonstrate experimentally displacement measurement of a light beam below the standard quantum limit. Multimode squeezed light is obtained by mixing a vacuum squeezed beam and a coherent beam that are spatially orthogonal. Although the resultant beam is not squeezed, it is shown to have strong internal spatial correlations. We show that the position of such a light beam can be measured using a split detector with an increased precision compared to a classical beam. This method can be used to improve the sensitivity of small displacement measurements
Cumulant expansion for studying damped quantum solitons
The quantum statistics of damped optical solitons is studied using
cumulant-expansion techniques. The effect of absorption is described in terms
of ordinary Markovian relaxation theory, by coupling the optical field to a
continuum of reservoir modes. After introduction of local bosonic field
operators and spatial discretization pseudo-Fokker-Planck equations for
multidimensional s-parameterized phase-space functions are derived. These
partial differential equations are equivalent to an infinite set of ordinary
differential equations for the cumulants of the phase-space functions.
Introducing an appropriate truncation condition, the resulting finite set of
cumulant evolution equations can be solved numerically. Solutions are presented
in Gaussian approximation and the quantum noise is calculated, with special
emphasis on squeezing and the recently measured spectral photon-number
correlations [Spaelter et al., Phys. Rev. Lett. 81, 786 (1998)].Comment: 17 pages, 13 figures, revtex, psfig, multicols, published in
Phys.Rev.
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