Quantum Entanglement

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Quantum Entanglement

Postby New Scientist on Sun Sep 07, 2008 3:09 pm

I have just read the article here: http://www.technologyreview.com/Infotech/21086/?a=f about researchers being able to control the position of a single electron in a silicon circuit.

I'm no scientist and my knowledge of quantum mechanics is laughable but I am a keen albeit frequently perplexed enthusiast. My puzzlement is when the article states that "the electron [was] in two places at once". I can't conceive how something can be in two places at once. Surely if there was an electron in one place and then a counterpart appeared somewhere else, the original electron is the one that hasn't moved from it's original position and the newcomer in a different location is merely a copy?

For something to be a different entity it surely requires that the entity is both:
- in another location (i.e. not sharing the space of another entity), and
- of itself (i.e. not part of the same matter of another entity)

Why is it the case that this '2nd' electron is not applicable to this definition?
New Scientist

Re: Quantum Entanglement

Postby Guest on Thu Mar 05, 2009 4:58 pm


I had a look at your article link. I don't think that it has anything to do with quantum entanglement, but instead with the superposition of states.

Basically, in quantum mechanics, a system gets described by a wavefunction ( a wave-like equation) which is itself related to the PROBABLILITIES of that system being in a certain state at the same time. If a system is prepared just right, then the wavefunction will show that there is a probability of the system being in two states at the same time ( be they energy, position, momentum...whatever). As long as the system is not directly observed, the system stays in this "superposition" of states and so is effectively in both at the same time.


The idea of something being in two places at once is not so far fetched. Electrons can be considered as both waves and particles and there is a famous experiment where an electron is fired at a screen with 2 slits. The interference pattern observed the other side of the screen shows that the electron must have gone through both slits at the same time just like a wave.

For an easily understandable overview of how this stuff can relate to quantum cryptography and computing, I highly recommend reading the last few chapters of "The Code Book" by Simon Singh. Its a popular science book which you can find in most bookshops and gives an overview of how quantum mechanics will be used in the next generation of code-making/breaking machines.

As for cloning, it is a mathematically proven law which states that a quantum object such as an electron cannot be copied exactly.

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