415 research outputs found
Demonstration of an optical quantum controlled-NOT gate without path interference
We report the first experimental demonstration of an optical quantum
controlled-NOT gate without any path interference, where the two interacting
path interferometers of the original proposals (Phys. Rev. A {\bf 66}, 024308
(2001), Phys. Rev. A {\bf 65}, 012314 (2002)) have been replaced by three
partially polarizing beam splitters with suitable polarization dependent
transmittances and reflectances. The performance of the device is evaluated
using a recently proposed method (Phys. Rev. Lett. {\bf 94}, 160504 (2005)), by
which the quantum process fidelity and the entanglement capability can be
estimated from the 32 measurement results of two classical truth tables,
significantly less than the 256 measurement results required for full quantum
tomography.Comment: 4 pages, 3 figure
Beating the Standard Quantum Limit with Four Entangled Photons
Precision measurements are important across all fields of science. In
particular, optical phase measurements can be used to measure distance,
position, displacement, acceleration and optical path length. Quantum
entanglement enables higher precision than would otherwise be possible. We
demonstrate an optical phase measurement with an entangled four photon
interference visibility greater than the threshold to beat the standard quantum
limit--the limit attainable without entanglement. These results open the way
for new high-precision measurement applications.Comment: 5 pages, 4 figures Author name was slightly modifie
Distinguishing genuine entangled two-photon-polarization states from independently generated pairs of entangled photons
A scheme to distinguish entangled two-photon-polarization states (ETP) from
two independent entangled one-photon-polarization states (EOP) is proposed.
Using this scheme, the experimental generation of ETP by parametric
down-conversion is confirmed through the anti-correlations between three
orthogonal two-photon-polarization states. The estimated fraction of ETP among
the correlated photon pairs is 37% in the present experimental setup.Comment: 5 pages, 2 figure
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