95 research outputs found
Spatial properties of entangled photon pairs generated in nonlinear layered structures
A spatial quantum model of spontaneous parametric down-conversion in
nonlinear layered structures is developed expanding the interacting vectorial
fields into monochromatic plane waves. A two-photon spectral amplitude
depending on the signal- and idler-field frequencies and propagation directions
is used to derive transverse profiles of the emitted fields as well as their
spatial correlations. Intensity spatial profiles and their spatial correlations
are mainly determined by the positions of transmission peaks formed in these
structures with photonic bands. A method for geometry optimization of the
structures with respect to efficiency of the nonlinear process is suggested.
Several structures composed of GaN/AlN layers are analyzed as typical examples.
They allow the generation of photon pairs correlated in several emission
directions. Photon-pair generation rates increasing better than the second
power of the number of layers can be reached. Also structures efficiently
generated photon pairs showing anti-bunching and anti-coalescence can be
obtained. Three reasons for splitting the correlated area in photonic-band-gap
structures are revealed: zig-zag movement of photons inside the structure,
spatial symmetry and polarization-dependent properties. Also spectral splitting
can be observed in these structures.Comment: 13 pages, 17 figure
Experimental joint signal-idler quasi-distributions and photon-number statistics for mesoscopic twin beams
Joint signal-idler photoelectron distributions of twin beams containing
several tens of photons per mode have been measured recently. Exploiting a
microscopic quantum theory for joint quasi-distributions in parametric
down-conversion developed earlier we characterize properties of twin beams in
terms of quasi-distributions using experimental data. Negative values as well
as oscillating behaviour in quantum region are characteristic for the
subsequently determined joint signal-idler quasi-distributions of integrated
intensities. Also the conditional and difference photon-number distributions
are shown to be sub-Poissonian and sub-shot-noise, respectively.Comment: 7 pages, 6 figure
Measurement-based tailoring of Anderson localization of partially coherent light
We put forward an experimental configuration to observe transverse Anderson
localization of partially coherent light beams with a tunable degree of
first-order coherence. The scheme makes use of entangled photons propagating in
disordered waveguide arrays, and is based on the unique relationship between
the degree of entanglement of a pair of photons and the coherence properties of
the individual photons constituting the pair. The scheme can be readily
implemented with current waveguide-on-a-chip technology, and surprisingly, the
tunability of the coherence properties of the individual photons is done at the
measurement stage, without resorting changes of the light source itself.Comment: 7 pages, 5 figures, additional correction
Surface spontaneous parametric down-conversion
Surface spontaneous parametric down-conversion is predicted as a consequence
of continuity requirements for electric- and magnetic-field amplitudes at a
discontinuity of chi2 nonlinearity. A generalization of the usual two-photon
spectral amplitude is suggested to describe this effect. Examples of nonlinear
layered structures and periodically-poled nonlinear crystals show that surface
contributions to spontaneous down-conversion can be important.Comment: 4 pages, 3 figure
Randomly poled crystals as a source of photon pairs
Generation of photon pairs from randomly poled nonlinear crystals is
investigated using analytically soluble model and numerical calculations.
Randomly poled crystals are discovered as sources of entangled ultra broad-band
signal and idler fields. Their photon-pair generation rates scale linearly with
the number of domains. Entanglement times as short as several fs can be
reached. Comparison with chirped periodically-poled structures is given and
reveals close similarity.Comment: 13 pages, 29 figure
Emission of photon pairs at discontinuities of nonlinearity in spontaneous parametric down-conversion
In order to fulfil the continuity requirements for electric- and
magnetic-field amplitudes at discontinuities of chi2 nonlinearity additional
photon pairs have to be emitted in the area of discontinuity. Generalized
two-photon spectral amplitudes can be used to describe properties of photon
pairs generated in this process that we call surface spontaneous parametric
down-conversion. The spectral structure of such photon pairs is similar to that
derived for photon pairs generated in the volume. Surface and volume
contributions to spontaneous down-conversion can be comparable as an example of
nonlinear layered structures shows.Comment: 11 pages, 8 figure
Photon-number distributions of twin beams generated in spontaneous parametric down-conversion and measured by an intensified CCD camera
The measurement of photon-number statistics of fields composed of photon
pairs, generated in spontaneous parametric down-conversion and detected by an
intensified CCD camera is described. Final quantum detection efficiencies,
electronic noises, finite numbers of detector pixels, transverse intensity
spatial profiles of the detected beams as well as losses of single photons from
a pair are taken into account in a developed general theory of photon-number
detection. The measured data provided by an iCCD camera with single-photon
detection sensitivity are analyzed along the developed theory. Joint
signal-idler photon-number distributions are recovered using the reconstruction
method based on the principle of maximum likelihood. The range of applicability
of the method is discussed. The reconstructed joint signal-idler photon-number
distribution is compared with that obtained by a method that uses superposition
of signal and noise and minimizes photoelectron entropy. Statistics of the
reconstructed fields are identified to be multi-mode Gaussian. Elements of the
measured as well as the reconstructed joint signal-idler photon-number
distributions violate classical inequalities. Sub-shot-noise correlations in
the difference of the signal and idler photon numbers as well as partial
suppression of odd elements in the distribution of the sum of signal and idler
photon numbers are observed.Comment: 14 pages, 14 figure
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