http://dailynews.yahoo.com/h/nm/20000315/tc/science_quantum_1.html
Wednesday March 15 2:49 PM ET
U.S. Scientists Closer to Making Supercomputer
By Bill Rosato
LONDON (Reuters) - U.S. scientists Wednesday moved a step closer to
developing a super-computer after looking at a branch of physics which
researches the physics of particles invisible to the human eye.
``In the language of quantum information science, we have realized a
four-quantum-bit logic gate. This system is relevant for the future
development of quantum information technology,'' the scientists said in the
journal Nature.
Conventional computers are based on binary ``switches,'' or bits, which can
either be switched on or off and computers carry out calculations utilizing
these switches.
Quantum theory holds that entities such as atoms do not decide whether they
exist in an on or off state until they are measured or interact with
something.
When they are not interacting the atoms exist in both states at once -- a
quantum superposition -- said Christopher Monroe, a researcher at the
National Institute of Standards and Technology (NIST).
Computers based on quantum physics would therefore be able to have switches
or ``qbits,'' which exist in both on and off states simultaneously.
A string of these quantum bits would consequently offer every possible on-off
combination and could carry out every calculation a computer needed
simultaneously, hugely increasing the computer's power and memory.
But maintaining several superpositions -- an entanglement -- is difficult. So
far it had only been maintained in systems of two or three qbits until US
researchers at NIST entangled four quantum particles, Rainer Blatt of the
University of Innsbruck said in an article in the journal nature.
Although many more particles would have to be ``entangled'' in order for a
quantum computer to become a reality the researchers were confident that the
technique could be used to create larger entanglements.
``Our technique is scalable to a lot more atoms. If we get to that level,
we'll not only bring the strangest feature of quantum mechanics closer to the
macroscopic world (the world visible to the naked eye), but we may also have
a quantum computer,'' Monroe said in a statement.
The new U.S. technique allows many-particle entanglement with ``comparatively
little effort'' and will be invaluable to further quantum state engineering,
Blatt said.
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