Quantum computing is a young research area of study focused on developing computer technology based on the principles of quantum theory, which explains the nature and behavior of energy and matter on the quantum (atomic and subatomic) level. It combines quantum mechanics with computer science, by studying models of computers based on quantum mechanics and trying to build such computers. This has resulted in many unexpected discoveries and opened up new frontiers.

## Quantum computing in Brief

A quantum computer is a device that performs quantum computing. Quantum computer is a special type of computer that uses qubits to model complex interactions between particles. Instead of taking a value of 1 or 0 as a bit in a normal computer, the qubit may be in a superposition of these States. The quantum computer, following the laws of quantum physics, would gain enormous processing power through the ability to be in multiple states, and to perform tasks using all possible permutations simultaneously.
Quantum computers compute by encoding information into a quantum state and performing quantum transformations on it. For certain problems, quantum computers can be exponentially faster than conventional (classical) computers, due to a larger space of states and transformations that they can use.
Quantum algorithms (such as Shorâ€™s factoring algorithm) can solve computational problems that are intractable for conventional computers.
Quantum mechanics enables quantum cryptography which provides an ultimate degree of security that cannot be achieved by conventional methods. These developments have generated an enormous interest in both building a quantum computer and exploring the mathematical foundations of quantum information.
Another application for quantum computing is artificial intelligence (AI). AI is based on the principle of learning from experience, becoming more accurate as feedback is given. This feedback is based on calculating the probabilities for many possible choices, and so AI is an ideal candidate for quantum computation. Some other applications include biomedical computations and simulations, financial modelling, particle physics modelling and other.

## Developments of Quantum Theory

Niels Bohr proposed the Copenhagen interpretation of quantum theory. This theory says that a particle cannot be endowed with properties until it is measured, since it is in all possible states.
Let's analyze the theory on the example of schrÃ¶dinger's cat. The cat is in a lead box, also there is placed a flask with cyanide. We do not know whether the cat is alive or not, because it is unknown whether he broke the flask or left it untouched. Only after opening the box we find out what became of the cat.
Another interpretation is the theory of the multiverse. It holds that for each individual state of an object there is a separate universe containing a single unique state of the object. There is a connection between these universes that affects the final state in one way or another.

## Quantum Programming

There have been two notable successes thus far with quantum programming. The first occurred in 1994 by Peter Shor, (now at AT&T Labs) who developed a quantum algorithm that could efficiently factorize large numbers. It centers on a system that uses number theory to estimate the periodicity of a large number sequence. The significance of the algorithm lies in the fact that with its help (when using a quantum computer with several thousand logical qubits) it becomes possible to hack cryptographic systems with a public key. For example, RSA uses the public key M, which is the product of two large primes. One of the ways to crack the cipher of the RSA is to find multipliers M with a sufficiently large M it is almost impossible to do this using well-known classical algorithms.

The other major breakthrough happened with Lov Grover of Bell Labs in 1996, with a very fast algorithm that is proven to be the fastest possible for searching through unstructured databases. The algorithm is so efficient that it requires only, on average, roughly N square root (where N is the total number of elements) searches to find the desired result, as opposed to a search in classical computing, which on average needs N/2 searches.

## Conclusion

Even though there are many problems to overcome, the breakthroughs in the last years have made some form of practical quantum computing not unfeasible, but there is much debate as to whether this is less than a decade away or a hundred years into the future. However, the potential that this technology offers is attracting tremendous interest from both the government and the private sector. Military applications include the ability to break encryptions keys via brute force searches, while civilian applications range from DNA modeling to complex material science analysis. It is this potential that is rapidly breaking down the barriers to this technology, but whether all barriers can be broken, and when, is very much an open question.

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