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ABSTRACT: We demonstrate a method to generate entangled photons with controlled spatial shape by parametric down conversion (PDC) in a 2D nonlinear crystal. A compact and novel crystal source was designed and fabricated, generating directly path entangled photons without the use of additional beam-splitters. This crystal supports two PDC processes, emitting biphotons into two beamlike modes simultaneously. Two coherent path entangled amplitudes of biphotons were created and their interference observed. Our method enables the generation of entangled photons with controlled spatial, spectral and polarization properties.
Optics Express 03/2013; 21(6):6689-96. · 3.59 Impact Factor
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ABSTRACT: Optical parametric down-conversion is a common source for the generation of
non-classical correlated photonic states. Using a parametric down-conversion
source and photon-number resolving detectors, we measure the two-mode
photon-number distribution of up to 10 photons. By changing the heralded
collection efficiency, we control the level of correlations between the two
modes. Clear evidence for photon-number correlations are presented despite
detector imperfections such as low detection efficiency and other distorting
effects. Two criteria, derived directly from the raw data, are shown to be good
measures for the degree of correlation. Additionally, using a fitting
technique, we find a connection between the measured photon-number distribution
and the degree of correlation of the reconstructed original two-mode state.
These observations are only possible as a result of the detection of high
photon number events.
10/2012;
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ABSTRACT: The role of the timing and order of quantum measurements is not just a
fundamental question of quantum mechanics, but also a puzzling one. Any part of
a quantum system that has finished evolving, can be measured immediately or
saved for later, without affecting the final results, regardless of the
continued evolution of the rest of the system. In addition, the non-locality of
quantum mechanics, as manifested by entanglement, does not apply only to
particles with spatial separation, but also with temporal separation. Here we
demonstrate these principles by generating and fully characterizing an
entangled pair of photons that never coexisted. Using entanglement swapping
between two temporally separated photon pairs we entangle one photon from the
first pair with another photon from the second pair. The first photon was
detected even before the other was created. The observed quantum correlations
manifest the non-locality of quantum mechanics in spacetime.
09/2012;
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ABSTRACT: Current photon entangling schemes require resources that grow with the photon
number. We present a new approach that generates quantum entanglement between
many photons, using only a single source of entangled photon pairs. The
different spatial modes, one for each photon as required by other schemes, are
replaced by different time slots of only two spatial modes. States of any
number of photons are generated with the same setup, solving the scalability
problem caused by the previous need for extra resources. Consequently,
entangled photon states of larger numbers than before are practically
realizable.
Physical Review Letters 04/2012; 109. · 7.37 Impact Factor
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ABSTRACT: We describe the full characterization of the biaxial nonlinear crystal BiB₃O₆ (BiBO) as a polarization entangled photon source using non-collinear type-II parametric down-conversion. We consider the relevant parameters for crystal design, such as cutting angles, polarization of the photons, effective nonlinearity, spatial and temporal walk-offs, crystal thickness and the effect of the pump laser bandwidth. Experimental results showing entanglement generation with high rates and a comparison to the well investigated β-BaB₂O₄ (BBO) crystal are presented as well. Changing the down-conversion crystal of a polarization entangled photon source from BBO to BiBO enhances the generation rate as if the pump power was increased by 2.5 times. Such an improvement is currently required for the generation of multiphoton entangled states.
Optics Express 10/2011; 19(21):20420-34. · 3.59 Impact Factor
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ABSTRACT: Bell state measurements, in which two quantum bits are projected onto a maximally entangled state, are an essential component of quantum information science. We propose and experimentally demonstrate the projection of two quantum systems with three states (qutrits) onto a generalized maximally entangled state. Each qutrit is represented by the polarization of a pair of indistinguishable photons-a biphoton. The projection is a joint measurement on both biphotons using standard linear optics elements. This demonstration enables the realization of quantum information protocols with qutrits, such as teleportation and entanglement swapping.
Physical Review Letters 04/2011; 106(13):130502. · 7.37 Impact Factor
