Student Nefedova E.A.

Kryvyi Rih Technical University

Quantum computers

Digital electronic computers, widely used nowadays, are created by means of semiconductors technologies.

Such computers in which logical operations are fulfilled with these classical, from physics point of view, conditions are named classical at present.

According to the prognosis of leading firms of the world 5 new types of comparators on nano-technologies are possible in the nearest future.

They are:

1. molecular-silicic computers;

2. biological computers;

3. neuron computers;

4. optical or optical-electronic computers;

5. quantum computers.

What is a quantum computer? A quantum computer is a hypothetical computing device, using for work quantum-mechanical effects, such as quantum confusion and quantum parallelism while implementing of quantum algorithms. It allows overcoming some limitations of classic computers.

Idea of quantum calculations, first stated by Yu. Manin and R. Fehman assumes, that the quantum system from L of two-levels quantum elements (q-bits – quantum bits) has 2L of linearly independent states, and, because of principle of quantum superposition, 2L-measured Hilbert space of states. Operation in quantum calculations corresponds the turn in this space. Thus, a quantum computing device can execute parallel 2L operations.

In the quantum computer control of one particle state causes a states change of all others. It results in quantum parallelism of calculations. Due to this effect such computer can have phenomenal productivity. For the certain types of calculations, for example difficult algorithms for cryptography or searches in giant data massifs, quantum computer can use hundreds of atoms «in tandem». On classical machine it would correspond implementation of milliards of operations simultaneously.

Simplified chart of calculation on the quantum computer looks as the following: initial state is logged to the q-bit system. Then system state or its subsystems states are changed by means of basic quantum operations. The value is measured at the end, and this is result of computer work.

It is evident that for working-out of any calculation two basic operations are quite enough. The quantum system gives a result that is hardly correct. But due to the small increase of operations in the algorithm it is possible to enlarge probability of correct result to unity.

By means of basic quantum operations it is possible to simulate work of ordinary logical elements, which ordinary computers are produced from. Therefore quantum computer will solve any task which is decided now almost for the same time.

It can turn that quantum computer is a sort of analog machine. But it is wrong: on fact it is a digital device, but it has analog nature.

Having only a few q-bit (q-bit – quantum bit –q-bit), it will be extremely useful for conducting of so-called Bell measuring, which can be used for realization of quantum teleportation. Probably, 10 q-bits are enough to realize one the quantum computer quantum encoding of Schumacher, which is essential for effective quantum cryptography. And it’s possible, that 100 bits will be enough quantum computer to become effective instrument of noise (maybe, partly de-coherent) quantum cryptographic connection.

As to appendixes it will be possible to create pairs of Einstein-Podolsk-Rosen, remote on large distances that will allow carrying out new strict experiments on validity verification of quantum theory. Now both in physics and in theory of calculations, active searches of new ways of quantum computers use are looked for.

Due to enormous speed of decomposition on simple multipliers, quantum computer will allow decrypting reports, coded through many popular cryptographic algorithms, such as RSA. Even now this algorithm is considered as comparatively reliable, because effective method of numbers decomposition on simple multipliers for classical computer is presently unknown.

Application of quantum mechanics ideas has already opened new epoch in the field of cryptography, because quantum cryptography methods give new possibilities in the field of messages transferring, which are impossible to «decipher» even in theory. Commercial standards of such systems have been already known and researched.