I have the following situation: About the polarization of the photon, I introduce the basis:
Horizontal polarization $|\leftrightarrow>=\binom{1}{0}$ Vertical polarization $|\updownarrow>=\binom{0}{1}$
The density matrix in this problem is:
$$\rho =\frac{1}{2}\begin{pmatrix} 1+\xi _{1} & \xi_{2}-i\xi _{3}\\ \xi_{2}+i\xi _{3} & 1-\xi _{1} \end{pmatrix}$$
The Stokes parameters are: $\xi _{1}, \xi _{2}, \xi _{3}$
The probability that if the photon has got lineal polarization whose axis forms an angle $\theta$ with de horizontal is:
$$|w>=cos\theta |\leftrightarrow>+sin\theta|\updownarrow>$$
$$ P_{\theta}=<w|\rho|w>=\frac{1}{2}\left ( 1+\xi_{1}cos(2\theta)+\xi_{2}sin(2\theta) \right )$$
Is there any value of the Stokes parameters for which this probability is zero?
