Quick question about Bloch's sphere

[Joao]

Hi everyone! Sorry for the bad English!

Please, I'm trying to understand Dirac' s notation and the Bloch sphere, but I'm stuck here:

I've read that, thinking about the Bloch Sphere as a compass, the North pole would be 1 and the South pole would be 0. And in the classical bits the bit could be only in North or South pole. In qubits, there would be a vector with 1 unit length (or something like it), since it is in a superposition of states 0 or 1 until it's measured. And the odds of it turning into 0 or 1 is determined by a complex number, in the power of two (not sure how to say it in english). And the odds of being 0 added to the odds of being 1 must sum to "1".

Ok, but in many places I've seen the Bloch Sphere represented as something like this: North means 1, east also 1, South- 1 and West -1.

And I've seen a vector representing "vertical polarizing" going straight to North and "horizontal polarizing" going straight to east...
(If I remember correctly).

Anyway, since the qubit can only "resolves" into 0 or 1, how can it be that the Bloch Sphere can have values like -1?

Thanks a lot! =)

 

[jedishrfu]

Here's some info on the Bloch sphere:

https://en.wikipedia.org/wiki/Bloch_sphere

In general, the labeling is arbitrary but for qubit notation folks set North to be |0> and South to be !1> vectors.

Here's the PBS series episode on Qubits:



and this one by Veritaseum:



There are many other youtube videos on its usage:

https://www.google.com/search?q=qub...pojbAhUDYawKHXjgA3AQ_AUIDSgE&biw=1312&bih=839

 

[Joao]

Thanks a lot! These videos really helped! =) thanks again! =)