2
$\begingroup$

Why does the Bloch sphere have a radius of 1?

Thank you so much! I am a quantum newbie, so forgive me if this is basic.

$\endgroup$
6
  • 3
    $\begingroup$ Downvotes: why? It seems to be an earnestly asked question. $\endgroup$ Commented Apr 22 at 20:57
  • 3
    $\begingroup$ To the question itself: the radius of a point on or in the Bloch sphere serves as a measure of the fidelity, which is bounded between 0 and 1. A points on the surface of the sphere corresponds to a pure qubit with fidelity = 1, while a point inside corresponds to a qubit in some mixed state, with fidelity <1 (but $\ge$ 0.) $\endgroup$ Commented Apr 22 at 21:00
  • 3
    $\begingroup$ Just to add, a pure single qubit state has to be described by a unit vector so that sum of probabilities of measurement of states 0 and 1 is 1. This may be helpful to understand Bloch sphere better: quantumcomputing.stackexchange.com/questions/37905/…, quantumcomputing.stackexchange.com/questions/9404/…, quantumcomputing.stackexchange.com/questions/10303/… $\endgroup$ Commented Apr 23 at 6:14
  • $\begingroup$ @MarkSpinelli: Absolutely agree, no point in downvoting. Everybody has to start learn from beginning. $\endgroup$ Commented Apr 23 at 6:19
  • $\begingroup$ Thank you so much for the help!! $\endgroup$ Commented Apr 23 at 20:35

0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.