3,112 research outputs found
Efficient polarization entanglement purification based on parametric down-conversion sources with cross-Kerr nonlinearity
We present a way for entanglement purification based on two parametric
down-conversion (PDC) sources with cross-Kerr nonlinearities. It is comprised
of two processes. The first one is a primary entanglement purification protocol
for PDC sources with nondestructive quantum nondemolition (QND) detectors by
transferring the spatial entanglement of photon pairs to their polarization. In
this time, the QND detectors act as the role of controlled-not (CNot) gates.
Also they can distinguish the photon number of the spatial modes, which
provides a good way for the next process to purify the entanglement of the
photon pairs kept more. In the second process for entanglement purification,
new QND detectors are designed to act as the role of CNot gates. This protocol
has the advantage of high yield and it requires neither CNot gates based on
linear optical elements nor sophisticated single-photon detectors, which makes
it more convenient in practical applications.Comment: 8 pages, 7 figure
Detector imperfections in photon-pair source characterization
We analyze how imperfections in single-photon detectors impact the
characterization of photon-pair sources. We perform exact calculations to
reveal the effects of multi-pair emissions and of noisy, non-unit efficiency,
non photon-number resolving detections on the Cauchy-Schwarz parameter, on the
second order auto-correlation and cross-correlation functions, and on the
visibilities of both Hong-Ou-Mandel and Bell-like interferences. We consider
sources producing either two-mode squeezed states or states with a Poissonian
photon distribution. The proposed formulas are useful in practice to determine
the impacts of multi-pair emissions and dark counts in standard tests used in
quantum optics.Comment: 9 pages, 11 figure
Long-distance practical quantum key distribution by entanglement swapping
We develop a model for practical, entanglement-based long-distance quantum
key distribution employing entanglement swapping as a key building block.
Relying only on existing off-the-shelf technology, we show how to optimize
resources so as to maximize secret key distribution rates. The tools comprise
lossy transmission links, such as telecom optical fibers or free space,
parametric down-conversion sources of entangled photon pairs, and threshold
detectors that are inefficient and have dark counts. Our analysis provides the
optimal trade-off between detector efficiency and dark counts, which are
usually competing, as well as the optimal source brightness that maximizes the
secret key rate for specified distances (i.e. loss) between sender and
receiver.Comment: 14 pages, 9 figures; published in Optics Expres
Limits on the deterministic creation of pure single-photon states using parametric down-conversion
Parametric down-conversion (PDC) is one of the most widely used methods to
create pure single-photon states for quantum information applications. However
little attention has been paid to higher-order photon components in the PDC
process, yet these ultimately limit the prospects of generating single-photons
of high quality. In this paper we investigate the impacts of higher-order
photon components and multiple frequency modes on the heralding rates and
single-photon fidelities. This enables us to determine the limits of PDC
sources for single-photon generation. Our results show that a perfectly
single-mode PDC source in conjunction with a photon-number resolving detector
is ultimately capable of creating single-photon Fock states with unit fidelity
and a maximal state creation probability of 25%. Hence an array of 17 switched
sources is required to build a deterministic (>99% emission probability) pure
single-photon source.Comment: 7 pages, 6 figure
Quantum states prepared by realistic entanglement swapping
Entanglement swapping between photon pairs is a fundamental building block in
schemes using quantum relays or quantum repeaters to overcome the range limits
of long-distance quantum key distribution. We develop a closed-form solution
for the actual quantum states prepared by realistic entanglement swapping,
which takes into account experimental deficiencies due to inefficient
detectors, detector dark counts, and multiphoton-pair contributions of
parametric down-conversion sources. We investigate how the entanglement present
in the final state of the remaining modes is affected by the real-world
imperfections. To test the predictions of our theory, comparison with
previously published experimental entanglement swapping is provided.Comment: 44 pages, 7 figures, Published with minor changes in Phys. Rev.
A conclusive experiment to throw more light on "light"
We describe a new realization of Ghose, Home, Agarwal experiment on wave
particle duality of light where some limitations of the former experiment,
realized by Mizobuchi and Ohtake, are overcome. Our results clearly indicate
that wave-particle complementarity must be understood between interference and
"whelcher weg" knowledge and not in a more general sense
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
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