From five dollar watches to multi-billion-dollar satellite networks, information processing devices are everywhere in our society. They have not only changed communication, entertainment, and scientific research; but the structure of the economy itself.

Today's information processing devices manipulate information using what is known as the "classical" approximation to the laws of physics. However, we have known for some time that there is a better description--the one provided by quantum mechanics. The study of how the laws of quantum mechanics will affect information processing is known as Quantum Information Processing, or QIP.

Research into the vast applications of QIP can be subdivided into the fields of quantum communication, quantum cryptography, quantum algorithms & complexity and quantum control & quantum computation.

There are at least two reasons why we should be interested in quantum information processing: The first is purely technological and is related to the shrinking of current information processing devices. The second is more fundamental and asks whether quantum mechanical effects can be harnessed to improve the capabilities of information processing devices and techniques.

Anyone who uses computers realizes that they are never as fast as we would like them to be. To make computers faster, the industry has relentlessly miniaturized transistors. In the mid-1960s, Gordon Moore, then chairman of Intel Corporation, noticed that the size of transistors was shrinking by roughly a factor of two every 18 months. There is no obvious reason why this rule, called Moore's law, should be obeyed; however, it has held true through the 1970s, '80s and the '90s and will be true for the first decade of the 21st century.

If we make the assumption that it will also be true for the next 15 to 20 years, transistors will become size of atoms, which are governed by the laws of quantum mechanics. Quantum mechanical effects will cause the transistors to make increasing numbers of errors which are not expected by the approximations of classical physics. To keep up with the pace of progress, it is essential that we understand and control these effects.

In the middle of the last century, many mathematicians explored the possibilities of computing devices. They devised some models of computation to capture what a realistic computer should be able to do and decided how much computing resources were needed to solve certain problems.

Problems that did not require an exponential amount of resources to solve on the model computer were classified as "easy," and the others as "hard." It was believed that any physical realization of a computer would preserve this classification. Recent work in quantum computation questions the heart of this assumption.

In 1994, a theoretical computer scientist named Peter Shor discovered an algorithm to efficiently factor numbers on a theoretical quantum computer. This problem, which may seem purely esoteric, is not without practical significance. The infeasibility of factoring large numbers is the foundation of the RSA encryption protocal which is widely used today for e-commerce.

The power of QIP comes from exploiting the quantum mechanical effect known as "superposition." The principle of superposition states that a quantum system that can be in two different states can also be in both at the same time. A quantum bit or qubit (the fundamental unit of quantum information) can thus be in the state 0 and 1 at the same time. Two quantum bits can simultaneously be in the states 00, 01, 10 and 11. If we have n quantum bits, they can be in two to the power of n (2ⁿ) states at once.

The work on factoring aroused the interest of the cryptographic community around the world. Scientists wanted to know if indeed it would be possible to build quantum computers and break these cryptographic codes. In addition, quantum computers could provide better search algorithms, more sensitive measuring instruments and the ability to efficiently simulate quantum physics. Efficient simulation of quantum physics would give a better understanding of various physical theories and their predictions, and could be applied to the design of new materials, chemicals and medicines.

The discovery of quantum error correction and recent proof-of-principle laboratory demonstrations have given researchers confidence that the power of quantum information processing can be harnessed. The transition to the quantum world is not a straightforward progression of today's technology. It is a leap not only in our way of controlling these systems but also a profound change in our understanding of what information is.

Yet another property of quantum mechanics is applicable to today's information processing techniques. The laws governing observation of quantum mechanical systems state that they can not be observed without also perturbing the system. In other words, they can not be observed without leaving a trace.

Quantum cryptography applies this property to cryptography techniques. Exploiting the properties of quantum mechanical systems allows the definitive detection of any eavesdroppers on a communication channel--a feat not possible with classical communication techniques.

Read another article about Quantum Computing at IQC