Nowadays the information technology is evolving rapidly. The search is primarily focused on the words compact and efficient. As the number of transistors per cm2 increases rapidly it s fair to say that as they get smaller, the next computational stage is going to be performed at atomic scale. At this level, the principles of classic physics and mechanics will be taken over by some new concepts: the quantum laws. The point of this is that quantum technology can offer much more than the classical one and although it s still in its primordial stages, this technology is opening new paths and new horizons in the new computational era. In a classical computational system a bit can have to physic or logic states: 1 or 0 or, respectively TRUE or FALSE. These two states can be represented in several ways. For instance the voltage between the plates of a capacitor. A charged capacitor could represent a bit value of 1 and an uncharged capacitor 0. Another way to represent or to code a bit of information could be two different electronic states of an atom But an atom can also have a superposition of two states. If a bit can exist in either of two states then it can also exist in a superposition of the two states. In other words, if we want to chose an atom as a physical bit, then it s possible to have more than 2 states. It can have both the value 1 and 0 and also any value in between. To understand the idea of a quantum object being in 2 states at once here is a very simple experiment.
This conclusion, in more technical terms, could be rephrased as fallow: the photon is in a coherent superposition of being in the transmitted beam and the reflected beam. In the same sort of manner, the atom can be prepared in a superposition of two different electronic states. Such a quantum system with two states is called a quantum bit, or a qubit and it can be prepared in superposition of its 2 logical states 0 and 1. [2] If we take a very simple example. Let s say we have 3 bits. With the classical computation methods, we can store in these 3 bits one of all 3 digit numbers in base 2 at a time. For example: 001, 010, 011 and so on. In total there are 23 = 8 possible numbers which can be stored in this 3 bit register. But a similar quantum 3 bit register would be able to store all these 8 numbers at the same time. So, a N bit quantum register would be able to store numbers 2N numbers at the same time. And the best thing about this is that operations can be performed on all of them at the same time. One way in which we could do this, is by taking quabits as atoms and then with tuned laser pulses we would be able to affect the atomic electronic states. In this way, we would be able to operate on all of them at the same time. During the operation all the numbers in the superposition are affected. This is a parallel computation.
In this way it would be able to perform in one computational step 2N classical operations. To get the same result with a classic ...
http://www.ce.jhu.edu/bhiriyur/Quantum%20Computation.ppt
[2] http://qubit.physics.ox.ac.uk/oldsite/intros/comp/comp.htm
[3] http://www.computer.org/intelligent/ex1999/pdf/x4009.pdf
[4] http://www-users.cs.york.ac.uk/~schmuel/comp/comp.html
[5] http://computer.howstuffworks.com/quantum-computer.htm/printable
[6] http://computer.howstuffworks.com/framed.htm?parent=quantum- computer.htm&url=http://www.connect.net/smalling/quantum1.htm
[7] http://qubit.physics.ox.ac.uk/oldsite/QuantumComputationFAQ.html
[8] http://qubit.physics.ox.ac.uk/oldsite/Intros_Tuts.html
[9] http://www.conect.net/smalling/quantum1.htm
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