So when the Hamiltonian is time-independent, we can define the Heisenberg state vectors by evolving the Schrödinger state vectors back in time:
|ψ⟩H=ˆU†(t)|ψ(t)⟩S=eiˆHt|ψ(t)⟩S
and we define operators
ˆAH(t)=ˆU†(t)ˆASˆU(t)
which gives us the Heisenberg equation: dˆAH(t)dt=−i[ˆAH(t),ˆH].
If, in the Schrödinger picture, we have a time-dependent Hamiltonian, the time evolution operator is given by
ˆU(t)=T[e−i∫t0ˆH(t′)dt′]
If I define the Heisenberg operators in the same way with the time evolution operators and calculate dAH(t)/dt I find
ddtˆAH(t)=dˆU†(t)dtˆASˆU(t)+ˆU†(t)ˆASdˆU(t)dt=iˆU†(t)^H(t)ˆASˆU(t)−iˆU†(t)ˆASˆH(t)ˆU(t).
At this point, I am not sure how to proceed. I can't commute ˆH(t) through ˆU(t) because [ˆH(t),ˆH(t′)]≠0. How do I show derive Heisenberg's equation for a time-dependent Hamiltonian?
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