# How could a quantum computer actually physically work ?

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fubear (

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May 18th, 2009

Is the idea of a quantum computer purely theoretical?

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## 8 Answers

Quantum computing is the concept of applying the rules of quantum physics on computing.

Meaning, as far as I’ve learned, it’s an attempt to expand the number of bits that a computer can understand to include more than just 1 and 0.

And as far as I’ve understood, if something like that ever sees the light, probably all the current rules of Digital Logic will become obsolete.

Hardly: as long as you have discrete numbers, digital logic applies. The use of binary math in computers is an accident of engineering, not an essential part of computation theory. There are two mathematical formalisms that are used to define computing: the Turing machine and the lambda calculus, and they have been proven to be expressively equivalent.

Quantum computing may result in things like massive parallelism, which will make our engineering of computers different and change the tradeoffs—for instance, cryptography will probably be changed, because our current approach to cryptography is based on the assumption that factoring large numbers takes a lot of processor time, and if quantum computing makes it possible to factor large numbers quickly, then cryptography will have to change—but unless something happens that makes the computer capable of calculating things that cannot be expressed by a Turing machine or the lambda calculus, it’s not going to make a theoretical difference.

IBM claims to have built a quantum computer. Lots of links on the Web about it.

@oratio – The popular multiplayer game called ‘Outfox the NSA’, but only version 1.0, because for the more recent games more than 7 qubits are required. IBM researchers are still juggling atoms around…

@mattbrowne

Yeah, thanks for mentioning that.

I forgot to mention that a Quantum Computer uses Qbits (Quantum bits) instead of bits.

Basically it uses superposition to represent and process information. There are several quantum algorithms that work on simulated quantum computers. I haven’t heard much in the way of a practical quantum computer yet though (aside from IBM’s new thing).

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