1. The problem statement, all variables and given/known data Hello, I'm a bit confused about the calculation of the expectation values. Normally, when I have a wave function of sort and I want to calculate the expectation value of some operator, I just insert it into the braket <ψ|A|ψ>, where ψ for example is a wave function composed out of eigenstates ψ=1/√3⋅(φ1+φ2+φ3) and I will just multiply those accordingly. My problem started when I was asked to calculate uncertainty for Lx and Ly, I keep seeing the expectation value it's being calculated like this: Lx=1/2⋅<lm|L++L-|lm>=0, with both bra-ket are for the same state. I don't understand, why can't the wavefunction be one that is composed out of several different eigenstates? 2. Relevant equations 3. The attempt at a solution When I calculated it at first, I did: <Lx>=1/2⋅<lm|L++L-|l'm'>, which confused me even more, since this is actually a calculation for the Lx matrix elements. What am I doing wrong here?