Hi, I have a question about the momentum eigenstates in a 1D infinite square well example. First of all, are there any eigenstates at all in this example? By explicitly applying the wavefunction(stationary states) which can be easily obtained from the boundary conditions, it can shown that the energy eigenstate doesn't have a corresponding momentum eigenstate(in the free particle case, each energy eigenstate corresponds to a momentum eigenstate) I believe it's because the particle is confined that it has a large uncertainty in momentum so no momentum eigenstates exist. But I,myself is not very convinced by this argument. Any input is appreciated.