RSA gets a reprieve?
Heyman, Michael
Michael.Heyman at sparta.com
Thu Jun 30 15:16:58 EDT 2005
From:
<www.newscientist.com/channel/info-tech/mg18625054.000>
ATTEMPTS to build quantum computers could run up
against a fundamental limit on how long useful
information can persist inside them. Exceed the
limit and information could just leak away,
making computation impossible...Rather than
remaining in a superposition of two states, a
qubit will spontaneously collapse into one state
or another (Physical Review Letters, vol 94,
p 230401). "When we discovered this we were
stunned," says van den Brink...the time limit
for decoherence seems to grow shorter as systems
get smaller. Zaanen says that for some of the
most promising qubit technologies the limit
would be about 1 second. It's not a problem at
the moment, he says, because researchers are
fighting to get coherence times up to around a
microsecond. "But this fundamental limit is
getting within reach."
This plus the "no-cloning theorem" means that if a quantum computer
cannot factor an RSA modulus in under a second, RSA will remain
unbreakable. (I'm not a quantum physicist or quantum computer programmer
so I don't even know if the no-cloning theorem, which states qubits of
unknown states cannot be copied, applies.)
-Michael Heyman
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