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Universe at your
finger tips
Raj
Kaushik
If you were to be cryogenically frozen today, just
like Mike Myers in Austin Powers: International Man of Mystery, and
defrosted in 2040, would you be able to recognise laptop computers?
Probably not, because unlike today’s computers that contain
processors and integrated circuits, the ones of the future may look
like tiny hour-glasses filled with liquid and flickering light
signals.
Work on developing quantum computers is already under
rapid progress. Christopher Monroe and his colleagues at the
University of Michigan’s Center for Optical Coherent and Ultrafast
Science have reported the first demonstration of laser-cooling of
individual trapped atoms in the April 2002 issue of Physical Review.
As individual atoms are used to store information, it is critical to
keep the atoms entirely isolated and protected from surrounding
interference. This can be achieved by cooling the atom to very low
temperatures.
In their experiment, Michigan researchers used
laser cooling to chill the single Cadmium atom to 0.001 degree
Celsius above absolute zero. Laser cooling removed unwanted motion
in the atom crystal without affecting the internal state of the
other atom. Partially based on the result of their experiment,
Monroe proposed a new “Architecture for a Large-Scale Ion-Trap
Quantum Computer,” with co-authors David Kielpinski, Massachusetts
Institute of Technology and David Wineland, National Institute of
Standards and Technology, in the June 13 2002 issue of the journal
Nature. Fred Chong of the University of California, Davis, Isaac
Chuang at MIT and John Kubiatowicz at UC Berkeley have already
launched a five-year project to build a superfast quantum computer.
Quantum Vs Classical
In classical computers, information
is processed using binary system, which essentially says that a
piece of information can be processed using two states or bits – 1
and 0. For example, a light bulb can exist in two states – either on
(1) or off (0). Classical world is governed by commonsense. For
example, a car can either be in Delhi or in Calcutta at a particular
instant, but it cannot exist at two distant locations
simultaneously.
Quantum world, on the other hand, is full of
weird phenomena. In this world, a particle can exist at two distant
locations at the same time. Just like “mass” is the property of a
car in the classical world; spin is the property of sub-atomic
particles in the quantum world.
A particle can have “Up” spin,
“Down” spin, or something in between. There is no way of knowing
with certainty whether a particle has an up spin or a down spin or
something in between at a particular point of time. Before a
particle is measured, for example, it could have a 90 per cent
chance of being “Up”, and a 10 per cent chance of being “Down”.
After the measurement, it takes on one of these two values.
Hence
unlike classical bits where states can be predicted with certainty,
a quantum bit – or “qubit” - can possess in up, down, and numerous
in-between values at the same time. This is called The Principle of
Superposition, which opens up a new world of exponentially fast
computing. Conventional computers process information in terms of
bits. A string of two bits can represent one out of four possible
numbers – zero (00) or 1(01) or 2(10) or 3(11). In a quantum
computer, qubits can be both one and zero at the same time. A string
of two qubits can therefore represent all four numbers in a single
operation.
As you add up qubits, the number of possibilities
that can be handled simultaneously grows exponentially. A
three-qubit computer can look at eight pieces of information (000,
001, 010, 011, 100, 101, 110, and 111) in a single operation.
Suppose you have 256 students in a school and you want to know the
name of the best ranking student. If you feed the data of 256
students to a classical eight-bit computer, it will perform multiple
operations to get the result. An eight-qubit quantum computer will
solve the problem in one operation.
Why Go Quantum
It is
logical to think why we need quantum computers when we already have
powerful super fast computers. Quantum computers are needed because
today we need to solve complex problems that supercomputers simply
cannot solve in our lifetime. Encryption usually makes the data
incomprehensible by scrambling it with numeric keys. For example,
you can send an encrypted message “Meet me at 317141025122523” to
your friend.
Your friend can decrypt and read the message easily
if you supply her with a decryption table. Encrypted messages in
such a simple fashion can also be decrypted by hackers using a hit
and miss technique. Today online transactions are common. When you
buy a book online, your data are encrypted using 128-bit algorithm,
which is almost impossible to break. To break a 128-bit code, an
algorithm needs to compute two to the power 128 (2128)
possibilities. This may take over trillions of years, which is much
greater time than the age of the universe.
But why anyone would
like to break a secure code. Isn’t it our intention to encrypt the
message in such a manner that it becomes impossible to crack? Or if
it can be broken at all, it should take such a long time that the
message turns of historic value. But what happens if terrorists
exchange encrypted messages over the Net and the government comes to
know only after the damage is done. The government would obviously
like to decrypt the data of terrorists and spies in real-time. To
read a message encrypted with a large key, a conventional computer
could take millions of years because it looks at all the
possibilities sequentially. A quantum computer would solve the
riddle in about a day or week, because it has potential to look at
many possibilities at the same time. Describing the future of
quantum computing, Stan Williams, director of Quantum Science
Research at Hewlett-Packard Labs, said, “This area has gone off like
a big bang. It’s breathtaking. The potential is so huge and it would
be so disruptive, it could completely change the way at least some
computing is done,”
A former project coordinator with the
National Council of Science Museums, India the author now works as
senior server developer in Toronto.
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