QUANTUM COMPUTATION - Groups - Action Tools

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Name: QUANTUM COMPUTATION
Website: http://www.qubit.org
Categories: Technology

Description:
WHAT IS QUANTUM COMPUTATION ?

A fundamentally new mode of information processing that can be performed only by harnessing physical phenomena unique to quantum mechanics (especially quantum interference).

WHAT IS QUANTUM MECHANICS ?

The deepest theory of physics; the framework within which all other current theories, except the general theory of relativity, are formulated. Some of its features are:

* Quantisation (which means that observable quantities do not vary continuously but come in discrete chunks or 'quanta'). This is the one that makes computation, classical or quantum, possible at all.
* Interference (which means that the outcome of a quantum process in general depends on all the possible histories of that process). This is the one that makes quantum computers qualitatively more powerful than classical ones.
* Entanglement (Two spatially separated and non-interacting quantum systems that have interacted in the past may still have some locally inaccessible information in common - information which cannot be accessed in any experiment performed on either of them alone.) This is the one that makes quantum cryptography possible.

WHAT'S ALL THIS ABOUT PARALLEL UNIVERSES ?

If you only want to predict what quantum computers will be able to do, you only need the equations of quantum mechanics. But if you want to explain how they will do it, you need to understand that the computer you can see and touch is only one tiny facet of a far larger object, which is just as real even though its existence is only detectable indirectly, through the computational work it does for us. The best way to describe the structure of a quantum computer is not at present clear, but in some respects it is like many computers similar to the one we see, performing different but correlated computations which affect each other through quantum interference.

In quantum computers, the effects of quantum interference are writ large. But the theory says that the whole of reality behaves in the same way. So the whole universe that we see around us is full of a subtle inner structure. This all-pervasive property is felt by some physicists to be best described as a multiverse, which contains many universes like ours, interacting only through quantum interference.
WHAT WILL QUANTUM COMPUTERS BE GOOD AT ?

These are the most important applications currently known:

* Cryptography: perfectly secure communication.
* Searching, especially algorithmic searching (Grover's algorithm).
* Factorising large numbers very rapidly (Shor's algorithm).
* Simulating quantum-mechanical systems efficiently.

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