选定对称规范:
A
^
=
1
2
(
−
B
y
B
x
0
)
{\displaystyle {\hat {\mathbf {A} }}={\frac {1}{2}}{\begin{pmatrix}-By\\Bx\\0\end{pmatrix}}}
对于哈密顿算符进行去量纲化:
H
^
=
1
2
[
(
−
i
∂
∂
x
−
y
2
)
2
+
(
−
i
∂
∂
y
+
x
2
)
2
]
{\displaystyle {\hat {H}}={\frac {1}{2}}\left[\left(-i{\frac {\partial }{\partial x}}-{\frac {y}{2}}\right)^{2}+\left(-i{\frac {\partial }{\partial y}}+{\frac {x}{2}}\right)^{2}\right]}
实际值可以通过引入
q
{\displaystyle q}
、
c
{\displaystyle c}
、
ℏ
{\displaystyle \hbar }
、
B
{\displaystyle \mathbf {B} }
及
m
{\displaystyle m}
等常数得出。
引入算符
a
^
=
1
2
[
(
x
2
+
∂
∂
x
)
−
i
(
y
2
+
∂
∂
y
)
]
{\displaystyle {\hat {a}}={\frac {1}{\sqrt {2}}}\left[\left({\frac {x}{2}}+{\frac {\partial }{\partial x}}\right)-i\left({\frac {y}{2}}+{\frac {\partial }{\partial y}}\right)\right]}
a
^
†
=
1
2
[
(
x
2
−
∂
∂
x
)
+
i
(
y
2
−
∂
∂
y
)
]
{\displaystyle {\hat {a}}^{\dagger }={\frac {1}{\sqrt {2}}}\left[\left({\frac {x}{2}}-{\frac {\partial }{\partial x}}\right)+i\left({\frac {y}{2}}-{\frac {\partial }{\partial y}}\right)\right]}
b
^
=
1
2
[
(
x
2
+
∂
∂
x
)
+
i
(
y
2
+
∂
∂
y
)
]
{\displaystyle {\hat {b}}={\frac {1}{\sqrt {2}}}\left[\left({\frac {x}{2}}+{\frac {\partial }{\partial x}}\right)+i\left({\frac {y}{2}}+{\frac {\partial }{\partial y}}\right)\right]}
b
^
†
=
1
2
[
(
x
2
−
∂
∂
x
)
−
i
(
y
2
−
∂
∂
y
)
]
{\displaystyle {\hat {b}}^{\dagger }={\frac {1}{\sqrt {2}}}\left[\left({\frac {x}{2}}-{\frac {\partial }{\partial x}}\right)-i\left({\frac {y}{2}}-{\frac {\partial }{\partial y}}\right)\right]}
这些算符的对易关系为:
[
a
^
,
a
^
†
]
=
[
b
^
,
b
^
†
]
=
1
{\displaystyle [{\hat {a}},{\hat {a}}^{\dagger }]=[{\hat {b}},{\hat {b}}^{\dagger }]=1}
.
哈密顿算符可记为:
H
^
=
a
^
†
a
^
+
1
2
{\displaystyle {\hat {H}}={\hat {a}}^{\dagger }{\hat {a}}+{\frac {1}{2}}}
朗道能级序数
n
{\displaystyle n}
是
a
^
†
a
^
{\displaystyle {\hat {a}}^{\dagger }{\hat {a}}}
的本征值。
角动量z方向上的分量为:
L
^
z
=
−
i
ℏ
∂
∂
θ
=
−
ℏ
(
b
^
†
b
^
−
a
^
†
a
^
)
{\displaystyle {\hat {L}}_{z}=-i\hbar {\frac {\partial }{\partial \theta }}=-\hbar ({\hat {b}}^{\dagger }{\hat {b}}-{\hat {a}}^{\dagger }{\hat {a}})}
利用其与哈密顿算符可对易,即
[
H
^
,
L
^
z
]
=
0
{\displaystyle [{\hat {H}},{\hat {L}}_{z}]=0}
,我们选定
L
^
z
{\displaystyle {\hat {L}}_{z}}
的本征值
−
m
ℏ
{\displaystyle -m\hbar }
为使
H
^
{\displaystyle {\hat {H}}}
与
L
^
z
{\displaystyle {\hat {L}}_{z}}
对角化的本征函数。易见,在第
n
{\displaystyle n}
个朗道能级上存在
m
≥
−
n
{\displaystyle m\geq -n}
。然而
m
{\displaystyle m}
的值可能非常大。在下面将推导系统表现出的有限简并度。
使用
b
^
†
{\displaystyle {\hat {b}}^{\dagger }}
可以使
m
{\displaystyle m}
减小一个单位同时使
n
{\displaystyle n}
保持不变,而
a
^
†
{\displaystyle {\hat {a}}^{\dagger }}
则可以使
n
{\displaystyle n}
增大一个单位,同时令
m
{\displaystyle m}
减小一个单位。类比量子谐振子,可以得到:
H
^
|
n
,
m
⟩
=
E
n
|
n
,
m
⟩
{\displaystyle {\hat {H}}|n,m\rangle =E_{n}|n,m\rangle }
E
n
=
(
n
+
1
2
)
{\displaystyle E_{n}=\left(n+{\frac {1}{2}}\right)}
|
n
,
m
⟩
=
(
b
^
†
)
m
+
n
(
m
+
n
)
!
(
a
^
†
)
n
n
!
|
0
,
0
⟩
{\displaystyle |n,m\rangle ={\frac {({\hat {b}}^{\dagger })^{m+n}}{\sqrt {(m+n)!}}}{\frac {({\hat {a}}^{\dagger })^{n}}{\sqrt {n!}}}|0,0\rangle }
在朗道规范与对称规范下,每个朗道能级上的简并轨道分别以量子数ky及
m
{\displaystyle m}
表征,每个朗道能级上单位面积的简并度是相同的。
可以证明选定下面这个波函数时,也可以得到上面得到的结果:
ψ
n
,
m
(
x
,
y
)
=
(
∂
∂
w
−
w
¯
4
)
n
w
n
+
m
e
−
|
w
|
2
/
4
{\displaystyle \psi _{n,m}(x,y)=\left({\frac {\partial }{\partial w}}-{\frac {\bar {w}}{4}}\right)^{n}w^{n+m}e^{-|w|^{2}/4}}
式中
w
=
x
+
i
y
{\displaystyle w=x+iy}
。
特别地,对于最低的朗道能级,即
n
=
0
{\displaystyle n=0}
时,波函数为任意一个解析函数与高斯函数的乘积:
ψ
(
x
,
y
)
=
f
(
w
)
e
−
|
w
|
2
/
4
{\displaystyle \psi (x,y)=f(w)e^{-|w|^{2}/4}}
。