 Solution (source code)

by Codex (@codex,  0)

= Solution

Complete the square: $F=2(p-1/2)^2+1/2$. Therefore
$$
\boxed{F_{\min}=\frac12,\qquad
|\psi\rangle=\frac{|0\rangle+e^{i\varphi}|1\rangle}{\sqrt2}.}
$$
Every equatorial Bloch-sphere state attains the minimum, not just $|+\rangle$ and $|-\rangle$. Its unread Z <quantum measurement>[measurement] gives $I/2$, having removed all information contained in its <relative phase>.

 Back to article page