# Measurements of angular momentum components

#### Winnie

If I make a measurement of Lz, and then make a measurement of Lx, then this value will not be deterministic, but how can I calculate the possible values that Lx can take?

Then if I make another measurement of Lz after the Lx measurement, what are the possible values of this? I think that this will be different from the first Lz measurement as measuring Lx will have changed the state of the system?

#### topsquark

Forum Staff
If I make a measurement of Lz, and then make a measurement of Lx, then this value will not be deterministic, but how can I calculate the possible values that Lx can take?

Then if I make another measurement of Lz after the Lx measurement, what are the possible values of this? I think that this will be different from the first Lz measurement as measuring Lx will have changed the state of the system?
You have the basic idea correct about the measurement. For the Lx measurement after the Lz you need to find the probability of each possible state that Lx could take. For example it would be typical for each value of lx (L = 1, then the lx runs over -1, 0, 1) would have the same probability, so you would have a 1/3 probability to find Lx in any particular state.

-Dan