Linked by Thom Holwerda on Fri 22nd Mar 2013 10:02 UTC

"But a powerful new type of computer that is about to be commercially deployed by a major American military contractor is taking computing into the strange, subatomic realm of quantum mechanics. In that infinitesimal neighborhood, common sense logic no longer seems to apply. A one can be a one, or it can be a one and a zero and everything in between - all at the same time. [...] Now, Lockheed Martin - which bought an early version of such a computer from the Canadian company D-Wave Systems two years ago - is confident enough in the technology to upgrade it to commercial scale, becoming the first company to use quantum computing as part of its business." I always get a bit skeptical whenever I hear the words 'quantum computing', but according to NewScientist, this is pretty legit.

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2010-03-08

Let me try to help you a bit understand what QM is and how it works.

One of the core tasks of physics is to describe what makes things move and how, whether the things in questions are tiny electrons or huge nebulas. Newton's laws of motion are a simple description of this which works pretty well at our scale, whereas Einstein's special and general theories of relativity are more accurate at high speed and large scales, and quantum mechanics (or QM) is the best at small scales.

QM and relativity can both be seen as extensions of Newton's laws to extreme scales, since if we try to apply them to "regular" objects, we'll get similar results as with Newton's laws. However, merging them into one single unified theory has proved to be extremely difficult for theoretical physicists. At this point, finding a satisfactory quantum description of gravitation, as described by the theory of general relativity, remains an open problem.

Now, how does the quantum description of the world differs from the one offered by classical mechanics? In a nutshell, it allows for some physical situations which are perfectly impossible in a Newtonian world, and simultaneously forbids some things which Newton's laws are perfectly fine with. Here are a few examples:

-Quantum objects' properties are not assumed to be perfectly known. What QM describes instead is the probabilities of finding something in a given state: at a given position, with a given speed...

-All these possible states of a system are not just statistical odds. Unless a measurement procedure leads the system to collapse in a single state, multiple "possible" states of a system exist simultaneously, and may thus interact with each other.

-QM's laws of motion are based on this latter effect, describing the probabilities of finding a system in a given state as changing in space and time in a manner similar to that a sound or like wave.

-All properties of a system are not independent, and it's impossible to simultaneously know all of them at once. This stem from the mathematics used to describe quantum states, which happen to be matching some real-world behaviors.

The reason why we're dealing with a theory that violates common sense in such a brutal way is that we have failed to find a saner description of the world which matches experiment so far. As an example, if the microscopic world followed Newton's laws of motion or their relativistic equivalents, electrons would crash into atom nuclei, many magnetic materials would have totally different properties, and we would still have to argue upon whether light is a wave or a stream of particles instead of having a maths that unify both descriptions.

Edited 2013-03-22 21:07 UTC