Formulate amplitudes with SymPy bra-ket states

[redeboer]

It would be great if the amplitudes are built up with bra-ket states. SymPy has some support for this:

import sympy as sp
from sympy.physics.quantum import qapply
from sympy.physics.quantum.spin import JzKet

j, m, a, b, c = sp.symbols("j m alpha beta gamma")
qapply(Rotation(a, b, c) * JzKet(j, m))

Note that this only works for states in a rest frame, but theoretically, one could provide implementations for a JzKet state with dynamics (by deriving from StateBase) and also define something like a LorentzBoost operator (just like the above Rotation).