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http://computer.howstuffworks.com/quantum-computer1.htm

I don't understand the final bit - how does entanglement allow scientists to know the value of the qubits? I can understand how it could allow them to perform complicated calculations without measuring the qubits, so they can remain in superposition throughout the operation. But how can they know the value of them through entanglement?Quantum computers also utilize another aspect of quantum mechanics known as entanglement. One problem with the idea of quantum computers is that if you try to look at the subatomic particles, you could bump them, and thereby change their value. But in quantum physics, if you apply an outside force to two atoms, it can cause them to become entangled, and the second atom can take on the properties of the first atom. So if left alone, an atom will spin in all directions; but the instant it is disturbed it chooses one spin, or one value; and at the same time, the second entangled atom will choose an opposite spin, or value. This allows scientists to know the value of the qubits without actually looking at them, which would collapse them back into 1's or 0's.

Thanks,