The laws of physics make things that are
very small -- like atomic particles -- act differently than objects in
the larger world where we reside.
One weird quantum property is entanglement, which allows properties
of particles like atoms, photons and electrons to remain linked, or synchronized,
regardless of the physical distance between the particles. Entanglement
is also very sensitive to disturbances and therefore difficult to measure.
Entanglement figures prominently in efforts to build quantum computers,
which use properties of particles to compute. Quantum computers promise
to be fantastically fast at certain types of large problems, including
those that would render today's cryptography useless. Entanglement also
figures in quantum cryptography schemes that offer theoretically perfect
Researchers from the University of Rome in Italy have pushed the
schemes forward by demonstrating a method for detecting entanglement.
The researchers generated entangled photons using a crystal and
a pair of laser beams. They showed that it was possible to detect entanglement
using three independent local measurements. The method is particularly
useful for determining if entanglement survived the transmission of photons
over a fiber optic line.
The method could be used to measure entanglement in any kind of
particles, including cold atoms, trapped ions, and electronic currents
in superconducting devices, according to the researchers.
The method could be used practically in five to ten years, according
to the researchers. The work appeared in the November 28, 2003 issue of
Physical Review Letters.
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