What's the fastest computer in the world? If you've seen the new Apple advertisement, you may say the iMac G5. Some of you may say a supercomputer at NASA and others may even say a mainframe at the pentagon. Well those answers are good, but they aren't close enough. The fastest computer in the world is "The Earth Simulator" in Japan. This computer is so fast that it can perform 35.86 trillion calculations per second - more than 4 times greater than the next-fastest machine. Especially considering that a trillion is a thousand billions or a million million. now what if I told you that, a "Quantum Computer" can be at least billion times faster than "The Earth Simulator" in Japan?

A Quantum computer is a special type of a computer that is based on quantum physics and not on conventional physics like out current digital computers. The reliance on quantum physics makes a quantum computer amazingly fast. But quantum before you start taking out your credit card in the hopes that you can but this baby, think again. A Quantum computer does not exist in reality. The fundamental idea behind quantum computers has been laid down on paper. It's just a matter of time before we have the technology to build the first quantum computer.

How it works:

You see a conventional computer hasn't changed in its fundamental principle over its life span. Sure, there have been drastic changes in computer technology since the early pioneering days of Charles Babbage (1791-1871), with mechanical gears leading to vacuum values to transistors and finally to integrated circuits boards. Although computers have become more compact and considerably faster in performing their task, the task remains the same: to manipulate and interpret an encoding of binary bits into a useful computational results. A bit is a fundamental unit of information, classically represented as ones or zeroes in your digital computer. Each classical bit is physically realized through a macroscopic physical system, such as the magnetization on a hard disk or the charge on a capacitor. Here lies a key difference between your classical computer and a quantum computer. Where a classical computer obeys the well understood laws of classical physics, a quantum computer is a device that harnesses physical phenomenon fundamentally new mode of information processing.

In a quantum computer, the fundamental unit of information (called a quantum bit or qubit), is not binary but rather more quaternary in nature. in other words, a qubit can exist in more than one state. This coexistence in multiple states is a function of quantum physics. A simple analog to this can be given by looking at any analog clock and comparing it to a digital clock. The digital clock is very  distinct in its hours, minutes and seconds. The digital watch "jumps" from one minute to the next. It is either 31 minutes past the hour or 32 minutes. There is no in between, there is no compromise. However compare that to an analog clock. See how there are "infinite" number of possibilities between the 31 minute maker and the 32 minute maker. These infinite number of possibilities represent the state of the clock, but we can't measure it precisely. That's why we say, "It's half past the hour." But unlike humans, in quantum computers, we can measure the multiple states of qubits, and we can measure than accurately. This is what makes quantum computers, we can measure the multiple states of qubits, and we can measure them very accurately. This is what makes quantum computers so powerful. So unlike a digital computer, where Boolean logic is applied to information represented as ones and zeros, quantum computers can apply gates to qubits and process nearly infinite amounts of information with one action. This fundamental difference is what makes quantum computer so much faster than conventional computers.

The idea of computational device based on quantum mechanics was first explored in 1970's and early 1980's by physicists and computer scientists. The problem was put forward after realizing that technology developments in this field will shrink computer parts down to the atomic level. At the atomic scale the physical laws that govern the behavior and properties of the circuit and inherently quantum mechanical in nature, not classical. This then raised the question of whether a new kind of computer could be devised based on the principles of quantum physics.

Till now, no full-fledged quantum computer has been built and most researched in the field agree that such a device lies still many years or decades in the future. Much progress has been promising for the implementation of a quantum computer. These systems must consist of a collection of well-defined distinct qubits. The qubits must be isolated from the environment but yet controllable from the computers perspective. This is the hardest to achieve in reality and no one has come close to accomplishing this.

Quantum and Cryptography:

Even though no real quantum computer has been created, much research into quantum information processing has been done. One such research was carried out by Peter Shor of AT&T's Bell Laboratories in New Jersey. Shor circulated in 1994 a preprint of a paper in which he set out a method for using quantum computers to crack an important problem in number theory, namely factorization. This in turn opened a new can of worms - of cryptographs. Cryptography is used to secure important transmission of data, such as financial transactions, government and corporate information. Conventional cryptography is based on public key distribution; which uses prime numbers to make it next to impossible to break the code. However Shor's algorithm challenged the belief that conventional cryptography was unbreakable.

Ironically, this cryptography problem can also be solved by quantum mechanics. The foundation of quantum mechanics is based on a principle which states that observation of a quantum system unavoidably disturbs this system. In other words, every time you open  the lid of the box to look in, the contents of the box change. The more you peek in, the more change happens. This natural phenomenon can be used to guarantee secret key distribution in quantum cryptography. Imagine you have a dozen leaping frogs in a shoebox. The size, weight, and texture of the frogs represent some code, which your friend knows from before. You mail this shoebox to your friend through the post. Now on its way to your friend, the mailman carrying the shoebox gets curious and open the shoebox. He finds leaping frogs in the box and some manage to jump out before he closes the lid. He delivers the box to your with a few missing frogs. You know from before that your friend mailed you a dozen frogs and since someone are missing, you can guess that the security of the box has been compromised.

That's exactly how quantum cryptography works. Two communicating parties agree on a random key by exchanging and manipulating quantum systems in such a way that the law of physics guarantee that an eavesdropper will either reveal themselves with near certainly or gain nearly no information about the key. Quantum key distribution is the most advanced applications of quantum information theory. There have been many successful experiments in realistic circumstances. In all these experiments the two-state quantum systems exchanged by the communicating parties and realized by photons, the qubit being for example encoded in the polarization of the photon. Most experiments to date uses optical fibers to transmit the photons. Currently, distances over ten of kilometers have been achieved at many places, for example at Los Alamos (USA), BT Labs (UK), the University of Geneva (CH).

2020 and beyond:

The pioneering field of quantum information has already  achieved a multitude of exciting and surprising insights - both in the foundations to problems of communication and computation. With many dedicated groups now working in this area, more surprises and breakthroughs are expected. Unfortunately, a quantum computer will not be emerging anytime within the next decade or so. Especially considering that quantum hardware still remains to be an developing field. It may be a matter of time before quantum computers will emerge as the superior computational devices at the very least, and perhaps one day make today's modern computer obsolete. Till then we have to make do with super computers as "The Earth Simulator" in Japan or our iMac G5.