81 research outputs found
Experimental violation of a Bell-like inequality with optical vortex beams
Optical beams with topological singularities have a Schmidt decomposition.
Hence, they display features typically associated with bipartite quantum
systems; in particular, these classical beams can exhibit entanglement. This
classical entanglement can be quantified by a Bell inequality formulated in
terms of Wigner functions. We experimentally demonstrate the violation of this
inequality for Laguerre-Gauss (LG) beams and confirm that the violation
increases with increasing orbital angular momentum. Our measurements yield
negativity of the Wigner function at the origin for \LG_{10} beams, whereas
for \LG_{20} we always get a positive value.Comment: 6 pages, 4 eps-color figures. Comments welcome
Multiparameter Quantum Metrology of Incoherent Point Sources: Towards Realistic Superresolution
We establish the multiparameter quantum Cram\'er-Rao bound for simultaneously
estimating the centroid, the separation, and the relative intensities of two
incoherent optical point sources using alinear imaging system. For equally
bright sources, the Cram\'er-Rao bound is independent of the source separation,
which confirms that the Rayleigh resolution limit is just an artifact of the
conventional direct imaging and can be overcome with an adequate strategy. For
the general case of unequally bright sources, the amount of information one can
gain about the separation falls to zero, but we show that there is always a
quadratic improvement in an optimal detection in comparison with the intensity
measurements. This advantage can be of utmost important in realistic scenarios,
such as observational astronomy.Comment: 5 pages, 3 figures. Comments welcome
Time-Multiplexed Measurements of Nonclassical Light at Telecom Wavelengths
We report the experimental reconstruction of the statistical properties of an
ultrafast pulsed type-II parametric down conversion source in a periodically
poled KTP waveguide at telecom wavelengths, with almost perfect photon-number
correlations. We used a photon-number-resolving time-multiplexed detector based
on a fiber-optical setup and a pair of avalanche photodiodes. By resorting to a
germane data-pattern tomography, we assess the properties of the nonclassical
light states states with unprecedented precision.Comment: 4.5 pages, 5 color figues. Comments welcome
Efficient algorithm for optimizing data pattern tomography
We give a detailed account of an efficient search algorithm for the data
pattern tomography proposed by J. Rehacek, D. Mogilevtsev, and Z. Hradil [Phys.
Rev. Lett.~\textbf{105}, 010402 (2010)], where the quantum state of a system is
reconstructed without a priori knowledge about the measuring setup. The method
is especially suited for experiments involving complex detectors, which are
difficult to calibrate and characterize. We illustrate the approach with the
case study of the homodyne detection of a nonclassical photon state.Comment: 5 pages, 5 eps-color figure
Intensity-based axial localization at the quantum limit
We derive fundamental precision bounds for single-point axial localization. For Gaussian beams, this ultimate limit can be achieved with a single intensity scan, provided the camera is placed at one of two optimal transverse detection planes. Hence, for axial localization there is no need of more complicated detection schemes. The theory is verified with an experimental demonstration of axial resolution 3 orders of magnitude below the classical depth of focus
Enhancing axial localization with wavefront control
Enhancing the ability to resolve axial details is crucial in
three-dimensional optical imaging. We provide experimental evidence showcasing
the ultimate precision achievable in axial localization using vortex beams. For
Laguerre-Gauss (LG) beams, this remarkable limit can be attained with just a
single intensity scan. This proof-of-principle demonstrates that microscopy
techniques based on LG vortex beams can potentially benefit from the introduced
quantum-inspired superresolution protocol.Comment: 10 pages, 6 figures. Comments welcom
Quantum polarization tomography of bright squeezed light
We reconstruct the polarization sector of a bright polarization squeezed beam
starting from a complete set of Stokes measurements. Given the symmetry that
underlies the polarization structure of quantum fields, we use the unique SU(2)
Wigner distribution to represent states. In the limit of localized and bright
states, the Wigner function can be approximated by an inverse three-dimensional
Radon transform. We compare this direct reconstruction with the results of a
maximum likelihood estimation, finding an excellent agreement.Comment: 15 pages, 5 figures. Contribution to New Journal of Physics, Focus
Issue on Quantum Tomography. Comments welcom
Local Sampling of the Wigner Function at Telecom Wavelength with Loss-Tolerant Detection of Photon Statistics
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