- #1
giova7_89
- 31
- 0
Here's my question: as soon as I learned Quantum Mechanics and Schrodinger equation, I saw a "similarity" with the equation one gets in classical mechanics for the evolution of a function in phase space. In QM one has:
[itex]
i\hbar\frac{d}{dt}\psi = \hat{H}\psi
[/itex]
and this is a evolution equation where [itex] \psi [/itex] is the element which evolves and it is an element of a space of functions.
If one represents this equation (considering one spinless particle) in the [itex] |\vec{x}> [/itex] basis, one gets the wave equation that everyone knows, where the hamiltonian on this basis acts on the state ket as
[itex]
-\frac{\hbar^2}{2m}\nabla^2 + U(\vec{x})
[/itex]
does.
In CM one has:
[itex]
\frac{d}{dt}f = \hat{L}f
[/itex]
where f is the element that evolves and it is an element of a space on functions, too. (here I assumed that the functions I want to evolve from time t0 to time t do not depend on t0 explicitly, otherwise I should have added [itex] \partial_t f [/itex] to that equation)
If one represents that equation in the [itex] |\vec{q},\vec{p}> [/itex] basis one gets:
[itex]
\frac{d}{dt}f (\vec{q},\vec{p}) = \{f(\vec{q},\vec{p}),H(\vec{q},\vec{p})\}
[/itex]
and if I solve Hamilton equations and get the hamiltonian flow [itex] \Phi^H_{(t,t_0)} [/itex], I know that the solution to the equation with initial condition f0 is:
[itex]
(e^{\hat{L}\Delta t}[f])(\vec{q},\vec{p}) = f(\Phi^H_{(t,t_0)}(\vec{q},\vec{p}))
[/itex]
(I assumed that H does not depend on time).
Then my question is: in CM i can solve the evolution equation for f (a PDE) by solving ODEs. Can a similar thing be done in QM with Schrodinger equation? Is there any vector field [itex] \vec{X} [/itex] whose associated flow (which i can find by solving [itex] \frac{d}{dt}\vec{x} = \vec{X} [/itex]) one can use to evolve the initial state ket of QM?
[itex]
i\hbar\frac{d}{dt}\psi = \hat{H}\psi
[/itex]
and this is a evolution equation where [itex] \psi [/itex] is the element which evolves and it is an element of a space of functions.
If one represents this equation (considering one spinless particle) in the [itex] |\vec{x}> [/itex] basis, one gets the wave equation that everyone knows, where the hamiltonian on this basis acts on the state ket as
[itex]
-\frac{\hbar^2}{2m}\nabla^2 + U(\vec{x})
[/itex]
does.
In CM one has:
[itex]
\frac{d}{dt}f = \hat{L}f
[/itex]
where f is the element that evolves and it is an element of a space on functions, too. (here I assumed that the functions I want to evolve from time t0 to time t do not depend on t0 explicitly, otherwise I should have added [itex] \partial_t f [/itex] to that equation)
If one represents that equation in the [itex] |\vec{q},\vec{p}> [/itex] basis one gets:
[itex]
\frac{d}{dt}f (\vec{q},\vec{p}) = \{f(\vec{q},\vec{p}),H(\vec{q},\vec{p})\}
[/itex]
and if I solve Hamilton equations and get the hamiltonian flow [itex] \Phi^H_{(t,t_0)} [/itex], I know that the solution to the equation with initial condition f0 is:
[itex]
(e^{\hat{L}\Delta t}[f])(\vec{q},\vec{p}) = f(\Phi^H_{(t,t_0)}(\vec{q},\vec{p}))
[/itex]
(I assumed that H does not depend on time).
Then my question is: in CM i can solve the evolution equation for f (a PDE) by solving ODEs. Can a similar thing be done in QM with Schrodinger equation? Is there any vector field [itex] \vec{X} [/itex] whose associated flow (which i can find by solving [itex] \frac{d}{dt}\vec{x} = \vec{X} [/itex]) one can use to evolve the initial state ket of QM?