Quantum Computing Update
Wed, 26 Dec 2001 

Quantum computing passes a key early test
http://www.siliconvalley.com/docs/news/svfront/quant122501.htm
On the surface it doesn't look like much: One of the world's strangest, most
cutting-edge computers has calculated that 15 can be divided by three or five.
But this was a quantum computer -- a billion billion molecules in a slosh of
liquid at the bottom of a test tube. It's a primitive example of a machine
that could, in theory, zip through calculations that would take millions of
years on today's fastest models.

And the calculation, performed by scientists at IBM's Almaden Research Center
in San Jose, was a milestone. It showed that a quantum computer, which just a
few years ago seemed the stuff of science fiction, can solve a type of problem
that is central to cracking computer codes that keep electronic data safe.
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IBM quantum computer solves code cracking problem
http://www.eetimes.com/story/technology/OEG20000822S0007
SAN JOSE, Calif. — IBM's Almaden Research Center unveiled the world's largest
quantum computer to date — a 5-bit computer squeezed onto a single molecule —
at the Hot Chips conference last week. The five fluorine atoms in the molecule
each represent a quantum bit, or "qubit," which made the computer the first
ever capable of solving a problem related to code cracking, called the
order-finding problem, in a single step.

"Every other computer in the world takes several steps to solve the
order-finding problem, but our quantum computer solved it in a single step,"
said Stanford University researcher Lieven Vandersypen. The quantum computer
was invented by IBM Almaden Research Center researcher Isaac Chuang, who led a
team of scientists that included fellow researchers Gregory Breyta and
Costantino Yannoni of IBM Almaden, professor Richard Cleve of the University
of Calgary, and researchers Matthias Steffen and Lieven Vandersypen from
Stanford University.
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IBM Advances Tiny Computer Power
Computers Made of Molecules Could Crack Toughest Codes
http://abcnews.go.com/sections/scitech/TechTV/techtv_quantumcompute011221.html
A quantum computer is a new kind of computer that uses individual atoms to
represent information," said Bill Risk, manager for the quantum information
group at IBM's Almaden Research Center, where the research took place.
"Because of the way it represents information and because it operates
according to principles of quantum physics, it can do certain kinds of
calculations much faster than conventional computers."

Conventional supercomputers can take an excruciatingly long time — sometimes
billions of years — to factor large numbers, even though the answer is
relatively simple to verify. Most of today's data-security schemes rely on
this factoring conundrum. By comparison, quantum computers could tackle those
problems with lightning speed.

"Someone's made the calculation that, for a 400-digit number, it would take
something like a billion or 10 billion years for a supercomputer using
conventional algorithms to factor that number. A quantum computer could do
that in a few months," Risk said.

Just as conventional computers store information in bits, which are the zeroes
and ones of binary code, quantum computers store data in qubits, which reside
in the nuclear spins of atoms. But qubits are much more powerful: While
electronic bits can only be ones or zeros, qubits can be both ones and zeroes
at the same time.

"Conventional bits are like a coin, they are either heads or tails," Risk
said. "Qubits can be, say, 90 percent heads and 10 percent tails."
This property makes quantum computers theoretically much faster at crunching
certain labor-intensive calculations, such as factoring large numbers or
searching large, unordered databases.
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Quantum Computing with Molecules
http://www.sciam.com/1998/0698issue/0698gershenfeld.html
Factoring a number with 400 digits--a numerical feat needed to break some
security codes--would take even the fastest supercomputer in existence
billions of years. But a newly conceived type of computer, one that exploits
quantum-mechanical interactions, might complete the task in a year or so,
thereby defeating many of the most sophisticated encryption schemes in use.

Sensitive databanks are safe for the time being, because no one has been 
able to
build a practical quantum computer. But researchers have now demonstrated the
feasibility of this approach. Such a computer would look nothing like the
machine that sits on your desk; surprisingly, it might resemble the cup of
coffee at its side.

We and several other research groups believe quantum computers based on the
molecules in a liquid might one day overcome many of the limits facing
conventional computers. Roadblocks to improving conventional computers will
ultimately arise from the fundamental physical bounds to miniaturization (for
example, because transistors and electrical wiring cannot be made slimmer than
the width of an atom). Or they may come about for practical reasons--most
likely because the facilities for fabricating still more powerful microchips
will become prohibitively expensive. Yet the magic of quantum mechanics might
solve both these problems.

The advantage of quantum computers arises from the way they encode a bit, the
fundamental unit of information. The state of a bit in a classical digital
computer is specified by one number, 0 or 1. An n-bit binary word in a typical
computer is accordingly described by a string of n zeros and ones. A quantum
bit, called a qubit, might be represented by an atom in one of two different
states, which can also be denoted as 0 or 1. Two qubits, like two classical
bits, can attain four different well-defined states ( 0 & 0,  0 & 1, 1 & 0, 
or 1 & 1).

But unlike classical bits, qubits can exist simultaneously as 0 & 1, with
the probability for each state given by a numerical coefficient. Describing a
two-qubit quantum computer thus requires four coefficients. In general, n
qubits demand 2n numbers, which rapidly becomes a sizable set for larger
values of n. For example, if n equals 50, about 1015 numbers are required to
describe all the probabilities for all the possible states of the quantum
machine--a number that exceeds the capacity of the largest conventional
computer. A quantum computer promises to be immensely powerful because it can
be in multiple states at once--a phenomenon called superposition--and because
it can act on all its possible states simultaneously. Thus, a quantum computer
could naturally perform myriad operations in parallel, using only a single
processing unit.
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A Quantum Leap for Computing
http://domino.research.ibm.com/comm/wwwr_thinkresearch.nsf/pages/quantum498.html

In Brief:
Systems in which information obeys the laws of quantum mechanics could far
exceed the performance of any conventional computer. Now that the principles
of quantum computing have been demonstrated in the lab, IBM scientists are
tackling the formidable task of building machines.

Although quantum computing is based on physical ideas elaborated in the 1920s,
the recognition that quantum mechanics might be useful for computing only
dawned on scientists in the 1980s. One reason is that the computers of the
1940s and '50s were built from vacuum tubes and other devices that were
clearly in the macroscopic realm, suggests IBM Fellow Charles Bennett, one of
the creators of the broader field of quantum information theory. Quantum
concepts simply didn't appear relevant.

Nevertheless, as physicists began to consider the physical limits of
computing, they were gradually led toward the quantum arena. First, IBM Fellow
Rolf Landauer discovered, in 1961, that energy is used up only during
irreversible operations, ones in which information is discarded. Based on that
work, Bennett showed in 1973 that fully reversible computation, which did not
consume any energy, was theoretically possible. Since quantum computations
also are reversible, experience gained in reversible programming in the 1970s
and '80s proved useful for designing quantum algorithms.

The path toward quantum computing began in 1980, when Paul Benioff of Argonne
National Laboratory published a quantum mechanical model for computation. Two
years later, Richard Feynman introduced the idea that any physical system
could be simulated with a quantum computer. It was David Deutsch at Oxford
University who, in 1985, first produced a mathematical description of a
universal quantum computer -- a machine that could be constructed out of
quantum elements and would in some ways be superior to a conventional
computer. But a flood of interest in the field did not emerge till 10 years
later.
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Harnessing the power of atoms, molecules
http://www.usatoday.com/news/science/stuffworks/2001-01-27-quantumcomputer.htm
Will we ever have the amount of computing power we need, or want? If, as
Moore's Law states, the number of transistors on a microprocessor continues to
double every 18 months, the year 2020 or 2030 will find the circuits on a
microprocessor measured on an atomic scale. And the logical next step will be
to create quantum computers, which will harness the power of atoms and
molecules to perform memory and processing tasks. Quantum computers have the
potential to perform certain calculations billions of times faster than any
silicon-based computer.

Scientists have already built basic quantum computers that can perform certain
calculations; but a practical quantum computer is still years away. If you
can't wait 20 or 30 years to delve into the details of the first computer with
a quantum processor, read this edition of How Stuff Will Work. You'll learn
what a quantum computer is and just what it'll be used for in the next era of
computing.
---------------------

The Hitchhiker's Guide To Quantum Computing
http://www.doc.ic.ac.uk/~nd/surprise_97/journal/vol1/spb3/
Although the future of quantum computing looks promising, we have only just
taken our first steps to actually realising a quantum computer. There are many
hurdles which need to be overcome before we can begin to appreciate the
benefits they may deliver. Researchers around the world are racing to be the
first to achieve a practical system, a task which some scientists think is
futile. David Deutsch - one of the ground breaking scientists in the world of
quantum computing - said himself that perhaps 'their most profound effect may
prove to be theoretical'.

In comparison the progress in quantum communications has been somewhat more
fruitful. Companies like BT have actually achieved working systems that are
able to use quantum effects to detect eavesdropping on a channel. Whether or
not such systems will prove practical remains to be seen.
Can we really build a useful quantum computer?
Who knows; in a quantum world, anything is possible!