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Mathematics for Quantum Physics
lectures
Commits
04a85057
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04a85057
authored
4 years ago
by
Michael Wimmer
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fix Schroedinger
parent
56ab99c6
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!9
DifferentialEquationsLecture2
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04a85057
...
@@ -240,13 +240,13 @@ is a $3$-rd order equation because of the third derivative with respect to x
...
@@ -240,13 +240,13 @@ is a $3$-rd order equation because of the third derivative with respect to x
in the equation.
in the equation.
To begin, we demonstrate that PDE's are of fundamental importance in physics,
To begin, we demonstrate that PDE's are of fundamental importance in physics,
especially in quantum physics. In particular, the Schr
\"
{o}
dinger equation,
especially in quantum physics. In particular, the Schr
ö
dinger equation,
which is of central importance in quantum physics is a partial differential
which is of central importance in quantum physics is a partial differential
equation with respect to time and space. This equation is very important
equation with respect to time and space. This equation is very important
because it describes the evolution in time and space of the entire description
because it describes the evolution in time and space of the entire description
of a quantum system $
\p
si(x,t)$, which is known as the wavefunction.
of a quantum system $
\p
si(x,t)$, which is known as the wavefunction.
For a free particle in one dimension, the Schr
\"
{o}
dinger equation is
For a free particle in one dimension, the Schr
ö
dinger equation is
$$i
\h
bar
\f
rac{
\p
artial
\p
si(x,t)}{
\p
artial t} = -
\f
rac{
\h
bar^2}{2m}
\f
rac{
\p
artial^2
\p
si(x,t)}{
\p
artial x^2}. $$
$$i
\h
bar
\f
rac{
\p
artial
\p
si(x,t)}{
\p
artial t} = -
\f
rac{
\h
bar^2}{2m}
\f
rac{
\p
artial^2
\p
si(x,t)}{
\p
artial x^2}. $$
...
@@ -259,7 +259,7 @@ the equation. In partial differential equations at least one such constant will
...
@@ -259,7 +259,7 @@ the equation. In partial differential equations at least one such constant will
arise from the time derivative and likewise at least one from the spatial
arise from the time derivative and likewise at least one from the spatial
derivative.
derivative.
For the Schr
\"
{o}
dinger equation, we could supply the initial conditions
For the Schr
ö
dinger equation, we could supply the initial conditions
$$
\p
si(x,0)=
\p
si_{0}(x)
\
&
\ \p
si(0,t) =
\p
si{t, L} = 0.$$
$$
\p
si(x,0)=
\p
si_{0}(x)
\
&
\ \p
si(0,t) =
\p
si{t, L} = 0.$$
...
@@ -287,7 +287,7 @@ physics.
...
@@ -287,7 +287,7 @@ physics.
## Separation of variables ##
## Separation of variables ##
Let us focus on the one dimensional Schr
\"
{o}
dinger equation of a free particle
Let us focus on the one dimensional Schr
ö
dinger equation of a free particle
$$i
\h
bar
\f
rac{
\p
artial
\p
si(x,t)}{
\p
artial t} = -
\f
rac{
\h
bar^2}{2m}
\f
rac{
\p
artial^2
\p
si(x,t)}{
\p
artial x^2}. $$
$$i
\h
bar
\f
rac{
\p
artial
\p
si(x,t)}{
\p
artial t} = -
\f
rac{
\h
bar^2}{2m}
\f
rac{
\p
artial^2
\p
si(x,t)}{
\p
artial x^2}. $$
...
@@ -336,7 +336,7 @@ needed to introduce a separation constant, which remains to be determined.
...
@@ -336,7 +336,7 @@ needed to introduce a separation constant, which remains to be determined.
### Boundary and eigenvalue problems ###
### Boundary and eigenvalue problems ###
Continuing on with the Schr
\"
{o}
dinger equation example from the previous
Continuing on with the Schr
ö
dinger equation example from the previous
section, let us focus on
section, let us focus on
$$-
\f
rac{
\h
bar^2}{2m}
\p
hi''(x) =
\l
ambda
\p
hi(x),$$
$$-
\f
rac{
\h
bar^2}{2m}
\p
hi''(x) =
\l
ambda
\p
hi(x),$$
...
@@ -477,7 +477,7 @@ the eigenfunctions of $L$.
...
@@ -477,7 +477,7 @@ the eigenfunctions of $L$.
In terms of hermitian operators and their eigenfunctions, the eigenfunctions
In terms of hermitian operators and their eigenfunctions, the eigenfunctions
play the role of the orthonormal basis. In reference to our running example,
play the role of the orthonormal basis. In reference to our running example,
the 1D Schr
\"
{o}
dinger equation of a free particle, the eigenfunctions
the 1D Schr
ö
dinger equation of a free particle, the eigenfunctions
$sin(
\f
rac{n
\p
i x}{L})$ play the role of the basis functions $
\k
et{u_n}$.
$sin(
\f
rac{n
\p
i x}{L})$ play the role of the basis functions $
\k
et{u_n}$.
To close our running example, consider the initial condition
To close our running example, consider the initial condition
...
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