- #1
gasar8
- 63
- 0
Homework Statement
We describe particle's movement with the Hamiltonian:
[tex] H=- \frac{\Delta E}{2} |0\rangle \langle0| + \frac{\Delta E}{2} |1\rangle \langle1|, [/tex]
where [itex] |0\rangle [/itex] and [itex] |1\rangle [/itex] are the ortonormal basis. Let:
[tex] |a\rangle = \frac{1}{\sqrt{2}}|0\rangle +\frac{i}{\sqrt{2}} |1\rangle. [/tex]
a) Find [itex]|b\rangle[/itex] state, so that it would form orthonormal basis of a Hilbert space with [itex]|a\rangle[/itex].
b) Find eigenvalues and eigenstates of a projector [itex]P_b=|b \rangle \langle b|[/itex].
c) Let a particle be in an [itex]|a \rangle[/itex] state at t=0. Find the time evolution of a wave function.
d) At t>0 we do a measurement of an operator[itex]P_b[/itex]. What are possible results of a measurement and what are their chances?
The Attempt at a Solution
a) We can write:
[tex] |b \rangle = A |0 \rangle + B |1 \rangle\\ \langle a|b \rangle=0 \\ \langle b|b \rangle=1.[/tex]
We get:
[tex] A=iB \\ |A|^2 + |B|^2=1,[/tex]
and finally:
[tex] |b \rangle = \frac{i}{\sqrt{2}} |0 \rangle +\frac{1}{\sqrt{2}} |1 \rangle. [/tex]
b) I am not sure what to do here? Do I have to use a projector on states?
[tex]P_b |b \rangle =|b \rangle \langle b|b \rangle [/tex]
I get only b state (because [itex]\langle b|b \rangle=1[/itex]) as an eigenfunction (?), but I'm not sure what are the eigenvalues then?
[tex]P_b |a \rangle =0 [/tex]c) [tex] | a,t \rangle = e^{-i \frac{H}{\hbar} t} | a,0 \rangle \\ H|0\rangle=-\frac{\Delta E}{2} |0\rangle \\ H|1\rangle= \frac{\Delta E}{2} |1\rangle \\ | a,t \rangle = \frac{1}{\sqrt{2}} e^{i \frac{\Delta E}{2 \hbar} t} |0 \rangle + \frac{i}{\sqrt{2}} e^{-i \frac{\Delta E}{2 \hbar} t} |1 \rangle [/tex]
Is this OK?
d) Here, I have got some problems. I am thinking - we can get 0, if the wave function is still in [itex] |a\rangle[/itex] state or (I don't know what) if the wave function gets into [itex] |b\rangle[/itex] state.
But on the other hand I think here must be something with [itex] |0\rangle[/itex] and [itex] |1\rangle[/itex] states, so that I use only square of absolute values of coefficients from c) for their chances (which are 50:50?).
Thank you for your answers.