Today's rudimentary quantum cryptography
systems send encryption key data over fiber-optic lines or through the
air, and each bit of the key is -- ideally -- encoded in a single photon.
Quantum cryptography systems promise potentially perfect security
because it is impossible to eavesdrop on bits encoded in single photons
without revealing the security breach.
Many quantum cryptography schemes involve encoding quantum bits,
or qubits, in the polarizations of photons and transmitting them over
fiber-optic lines. Polarization is the orientation of a photon's electric
But the polarizations of photons tend to rotate as the photons
travel through optical fibers. Researchers have devised several schemes
for overcoming polarization rotation, including sending photons on round
trips to reverse the effect and monitoring the lines to compensate for
changes. These approaches introduce overhead and don't work if the rate
of change is too fast, however.
Researchers from the University of Waterloo in Canada have come
up with a way to make quantum signals that can better withstand this kind
The method takes advantage of decoherence-free subspaces, which
encode a logical qubit in two or more physical qubits. Each qubit is encoded
using the polarization states of three or four photons. A qubit is encoded
in the relationship of three or four photons, so when a fiber optic line
rotates the polarization it affects all of the qubit's photons equally,
thus preserving the qubit.
The protocol could be implemented in today's technology, according
to the researchers. The work appeared in the January 9, 2004 issue of
Physical Review Letters.
Material grabs more sun
Molecule makes electric
Optical quantum memory
micro 3D objects
Tiny rotors spin
Nanotube forms drive
nanotubes in resin
View from the High Ground Q&A
How It Works
News | Blog
Buy an ad link