The
subject of quantum computing brings together ideas from classical information
theory, computer science, and quantum physics. This document aims to summarize
not just quantum computing, but the whole subject of quantum information theory.
It turns out that information theory and quantum mechanics fit together very well.
In order to explain their relationship, the paper begins with an introduction
to classical information theory .The principles of quantum mechanics are then
outlined. The EPR-Bell correlation
and quantum entanglement in general, form the essential new ingredient, which
distinguishes quantum from classical information theory, and, arguably, quantum
from classical physics. Basic quantum information ideas are described, including
key distribution, teleportation, the universal quantum computer and quantum algorithms.
The common theme of all these ideas is the use of quantum entanglement as a computational
resource.

Experimental methods
for small quantum processors are briefly sketched, concentrating on ion traps,
super conducting cavities, Nuclear magnetic resonance imaging based techniques,
and quantum dots. "Where a calculator on the Eniac is equipped with 18000
vacuum tubes and weighs 30 tons, computers in the future may have only 1000 tubes
and weigh only 1 1/2 tons" Popular Mechanics, March 1949.Now,
if this seems like a joke, wait a second. "Tomorrows computer might well
resemble a jug of water" .This for sure is no joke. Quantum computing is
here. What was science fiction two decades back is a reality today and is the
future of computing. The history of computer technology has involved a sequence
of changes from one type of physical realization to another --- from gears to
relays to valves to transistors to integrated circuits and so on. Quantum computing
is the next logical advancement. Today's
advanced lithographic techniques can squeeze fraction of micron wide logic gates
and wires onto the surface of silicon chips. Soon they will yield even smaller
parts and inevitably reach a point where logic gates are so small that they are
made out of only a handful of atoms.