Thus far computation has rested on the laws of physics as they stood in the 19th Century; what physicists refer to as 'classical mechanics'. Quantum Computers operate on an entirely new paradigm for information processing. The laws of physics which bind them are those of 'Quantum Mechanics'.

In its simplest form a classical computer operates by inputting a set of instructions (algorithm) into an operational state of the computer. The computer then changes its state along the guidelines of the algorithm and produces its output. Often this output will then be fed back into the computer to produce further output.

The 'state' of the computer is determined by the orientation of the bits inside the computer. Each of these bits can be in one of two states, which we associate with either a 0 or a 1. The guiding principles of this type of computation (Classical Computation) were outlined in 1936 by the English Mathematician Allen Turing.

Quantum Computers use qubits instead of bits. These qubits can be in both states simultaneously. Hence a quantum computer's algorithm can act on all states of the computer at once. The fundamental operational techniques of a quantum computer transcend those outlined by Turing, and open the way for a radical (and potentially far more powerful) form of computation. To understand this better, it is best to elucidate three basic differences between the Classical and Quantum Computer.

A classical computer takes an input algorithm, processes it, and generates output.

1. Bit to Qubit

The 'bit' is the building block of the classical computer. It is a physical system that can be in one of two states.

We denote either a 0 or 1 to represent each of these states. As common sense would dictate, the bit can be in only one of the two states. The Quantum Computer however is built of qubits.

These qubits have states analogous to the classical situation of 0 or 1, as well as being able to represent intermediate states simultaneously. This is achieved by the wavelike nature of the qubits superimposing themselves upon one another. This property of qubits allows the Quantum Computer to represent all internal states of the computer simultaneously. Hence upon an algorithmic input, the Quantum Computer can run all possible variations at once, rather than having to repeat the process for each possibility.

2. More Logic Gates

Classical Computers operate by using binary logic. Statements such as 'and' and 'or' are represented symbolically and generate a single output bit. For example: if two bits are the same, generate a 1; if they are different, generate a 0. Quantum Computers have an expanded set of logic gates. While theoretically being able to represent all Classical Logic Gates, Quantum Logic Gates are also able to generate a superposition of states as their output. This expanded set of logic gates gives us the potential to generate far greater processing power in Quantum Computers.

3. The Ineffable Nature of States

Coupled with this vast increase in potential information processing power of the Quantum Computer is the fact that it is impossible to ever know exactly what state the computer is in at a given time. Because the Quantum Computer is in a delicate superposition of all states, to determine what state it is in will collapse the superposition and force the computer into one particular state, thus losing all the information about the other states. All we can hope to achieve is to extract some of the information contained inside the Quantum Computer. Designing algorithms for Quantum Computers is thus always a delicate balance of utilizing the vast increase in processing ability, while dealing with the restricted amount of extractable information.

Although Classical Computers are amazingly powerful, and their processing ability appears to be on a steady increase (for the next few decades at least) there are some problems which it seems unlikely they will ever be able to solve. The vast number of variations in combinations of states in problems such as Genome Sequencing, or Quantum Mechanical Simulations would require Classical Computers to run algorithms for a very long time. In some cases this timeframe is longer then the age of the universe! As Quantum Computers can represent all states simultaneously, it is in situations such as this that their processing potential becomes particularly exciting.

Quantum Computers would also possess the ability to 'crack' any of the 'uncrackable' codes of today's encryption techniques. These codes are secure due to the use of extremely large prime numbers in their encryption. Factorization of large numbers is, however, one of the few Quantum Algorithms currently known. Thus, in an age where information and its security is of paramount importance, Quantum Computers hold the keys to all the locks. Fortunately Quantum Computers also have the potential for new locks, by utilizing such things as 'entanglement' and 'transportation'.

Vincent Conrad