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View Full Version : [SOLVED] QM: system with two lin. independent states


jacobrhcp
Dec28-07, 08:47 AM
1. The problem statement, all variables and given/known data

Imagine a system with just two linear independent states:

|1>=(1,0) and |2>=(0,1) (these are actually column matrices, but I don't know how to type those in tex)

|\Psi>=a|1>+b|2>=(a,b), also |a|^2+|b|^2=1

suppose the hamiltonian is a 2x2 matrix with entries j,g above and g,j below, (g,j \in R>0).

The time-independent schroding equation reads

H |\Psi>=i h/(2 pi) d/dt(|\Psi>)

a) find the eigenvalues and eigenvectors of this hamiltonian
b) suppose the system starts out at t=0 in |1>, what is the state at time t?

3. The attempt at a solution

I thought of solving the time-independent SE;

ja+gb= i h/(2 pi) d/dt(a)
ga+jb= i h/(2 pi) d/dt(b)

but does this mean g=0? And if so, how do I get any further. I'm stuck.

Dick
Dec28-07, 09:19 AM
Change to the basis where H is diagonal.

jacobrhcp
Jan1-08, 08:40 AM
solved it with a friend today =)