Published on Dec 17, 2015

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. On the atomic scale matter obeys the rules of quantum mechanics, which are quite different from the classical rules that determine the properties of conventional logic gates. So if computers are to become smaller in the future, new, quantum technology must replace or supplement what we have now.

Quantum technology can offer much more than cramming more and more bits to silicon and multiplying the clock-speed of microprocessors. It can support entirely new kind of computation with qualitatively new algorithms based on quantum principles!