- #1
James MC
- 174
- 0
Standard Pauli spin matrices are:
Sx:
$$\left(\begin{array}{cc}0&1/2\\1/2&0\end{array}\right)$$
Sz:
$$\left(\begin{array}{cc}1/2&0\\0&-1/2\end{array}\right)$$
The Sz eigenvectors are Z+ = (x=1,y=0) and Z- = (x=0,y=1). These yield eigenvalues 1/2 and -1/2 respectively. Similarly, eigenvectors of Sx are defined to guarantee eigenvalues 1/2 and -1/2 (e.g. by making X+ = (1/2(x=sqrt(2),y=sqrt(2))).
My question is this:
Do they need to be those values? What is stopping me from instead defining the operators as follows:
Sx:
$$\left(\begin{array}{cc}0&1\\1&0\end{array}\right)$$
Sz:
$$\left(\begin{array}{cc}1&0\\0&-1\end{array}\right)$$
Retain the Sz eigenvectors. That gives eigenvalues +1 and -1. Make the Sx eigenvectors such that eigenvalues are +1 and -1 (e.g. by making X+ = (x=1/sqrt(2),y=1/sqrt(2)).
Is there some reason why the spin matrices don't take this form instead?
A more general question from which this spawns: Hermitian operators are invoked so as to sure that eigenvalues are always real numbers. But why should they be real numbers? What's wrong with complex eigenvalues?
Interested in your thoughts!
Sx:
$$\left(\begin{array}{cc}0&1/2\\1/2&0\end{array}\right)$$
Sz:
$$\left(\begin{array}{cc}1/2&0\\0&-1/2\end{array}\right)$$
The Sz eigenvectors are Z+ = (x=1,y=0) and Z- = (x=0,y=1). These yield eigenvalues 1/2 and -1/2 respectively. Similarly, eigenvectors of Sx are defined to guarantee eigenvalues 1/2 and -1/2 (e.g. by making X+ = (1/2(x=sqrt(2),y=sqrt(2))).
My question is this:
Do they need to be those values? What is stopping me from instead defining the operators as follows:
Sx:
$$\left(\begin{array}{cc}0&1\\1&0\end{array}\right)$$
Sz:
$$\left(\begin{array}{cc}1&0\\0&-1\end{array}\right)$$
Retain the Sz eigenvectors. That gives eigenvalues +1 and -1. Make the Sx eigenvectors such that eigenvalues are +1 and -1 (e.g. by making X+ = (x=1/sqrt(2),y=1/sqrt(2)).
Is there some reason why the spin matrices don't take this form instead?
A more general question from which this spawns: Hermitian operators are invoked so as to sure that eigenvalues are always real numbers. But why should they be real numbers? What's wrong with complex eigenvalues?
Interested in your thoughts!