Saturday, 15 September 2018

quantum mechanics - Heisenberg Picture with a time-dependent Schrödinger Hamiltonian


So when the Hamiltonian is time-independent, we can define the Heisenberg state vectors by evolving the Schrödinger state vectors back in time:


|ψH=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[eit0ˆH(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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