I am reading Quantum Computation and Quantum Information by Nelson and Chuang myself and came across the Bloch Sphere representation of a quibit on page 15 (equation 1.4) as:(adsbygoogle = window.adsbygoogle || []).push({});

[tex]|\psi> = \cos\frac{\theta}{2} |0> + e^{i\psi}\sin\frac{\theta}{2} |1>[/tex]

I have two questions:

1. What is the motivation behind such a representation (other than the fact that the sum of the squares of the coefficients of [itex]|0>[/itex] and [itex]|1>[/itex] equals 1)?

2. Why use [itex]\theta/2[/itex] rather than [itex]\theta[/itex]?

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# Simple question regarding the Bloch Sphere

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