- #1
pellman
- 684
- 5
How does one determine the state of a system from observations?
Let us look at a simple example: the spin of a fermion. Any state of the system is a superposition of up and down eigenstates. Denote the coefficients in this superposition by a and b. The question here amounts to determining a and b up to an overall phase.By performing spin measurements on many identically prepared systems we can determine the ratio |a|^2 / |b|^2. But how do we get the relative phase?
Let us look at a simple example: the spin of a fermion. Any state of the system is a superposition of up and down eigenstates. Denote the coefficients in this superposition by a and b. The question here amounts to determining a and b up to an overall phase.By performing spin measurements on many identically prepared systems we can determine the ratio |a|^2 / |b|^2. But how do we get the relative phase?