Initialisierung

SetOptions[Plot,LabelStyle->{FontFamily->"Helvetica",FontSize->20}];

En[n1_,n2_,L_,m_]:=(((ℏ^2)(π^2))/(2 m (L^2)))((n1^2)+(n2^2))
ψ[n1_,n2_,L_,x_,y_]:=(Sqrt[4/(L^2)])Sin[((n1 π x)/L)]Sin[((n2 π y)/L)]

h = 6.626068×(10^(-34));
ℏ=(h/(2π));
m=9.1 (10^(-31));
nmax=3;
Lmax=1.;
nm=(10^(-6));

ShowCodeButton:=DynamicModule[{mode=1(*show*)},SelectionMove[EvaluationNotebook[],All,EvaluationCell];
SetOptions[NotebookSelection[EvaluationNotebook[]],CellOpen->False];
Button[Dynamic[If[mode==1,"Show code","Hide code"]],If[mode==1,SelectionMove[EvaluationNotebook[],All,EvaluationCell];
SelectionMove[EvaluationNotebook[],Previous,Cell];SetOptions[NotebookSelection[EvaluationNotebook[]],CellOpen->True];
mode=2,
(*else*)
SelectionMove[EvaluationNotebook[],All,EvaluationCell];
SelectionMove[EvaluationNotebook[],Previous,Cell];SetOptions[NotebookSelection[EvaluationNotebook[]],CellOpen->False];
mode=1
]
]
]

Plots

ShowCodeButton
Manipulate[Show[Plot[Evaluate@Flatten[Table[((ψ[n1,n2,L/Lmax,x,y])^2)0.03+En[n1,n2,L nm,m]/h/(10^9),{n1,1,nmax},{n2,1,nmax}],1],{x,0,L},Filling->Flatten[Table[(n1-1)nmax+ n2->En[n1,n2,L nm,m]/h/(10^9),{n1,1,nmax},{n2,1,nmax}],1],Frame->True,PlotRange->{{-0.07 nmax,1.1}Lmax ,{-0.1,1.2}En[nmax,nmax,Lmax nm,m]/h/(10^9)},PlotStyle->ColorData[1,"ColorList"],ImageSize->600,Axes->False,FrameLabel->{"x [nm]","Energie [GHz h]"},Epilog->Table[Inset[Style[(Subscript["E", ToString[n1]<>ToString[n2]]),16,FontFamily->"Helvetica"],{-0.055n1,En[n1,n2,L nm ,m]/h/(10^9)}],{n1,1,nmax},{n2,1,nmax}]],Graphics[{Line[{{0,#},{L,#}}]&/@Flatten[Table[En[n1,n2,L nm,m]/h/(10^9),{n1,1,nmax},{n2,1,nmax}],1],LightGray,Rectangle[{L ,0},{1.1 Lmax ,1.2 En[nmax,nmax,Lmax nm,m]/h/(10^9)}],Rectangle[{-0.07nmax Lmax ,0},{0,1.2En[nmax,nmax,Lmax nm,m]/h/(10^9)}],Rectangle[{-0.07 nmax Lmax ,-0.1En[nmax,nmax,Lmax nm,m]/h/(10^9)},{1.1 Lmax ,0}]}]],{{L,Lmax,"L [nm]"},(10^(-13)),Lmax ,ControlType->Slider,Appearance->"Labeled"},{{y,0.5,"y [nm]"},0,L ,ControlType->Slider,Appearance->"Labeled"},LabelStyle->Large,SaveDefinitions->True]

ShowCodeButton
Manipulate[Show[Plot3D[Evaluate@(((ψ[n1,n2,L/Lmax,x,y])^2)0.1+En[n1,n2,L nm,m]/h/(10^9)),{x,0,L},{y,0,L},ColorFunction->"RedBlueTones",PlotRange->{{-0.1,1.1}Lmax,{-0.1,1.1}Lmax ,{-0.1,1.5}En[nmax,nmax,Lmax nm,m]/h/(10^9)},ImageSize->600,Axes->True,AspectRatio->1,ViewPoint->{1.8140284791827042`,-2.635547928919315`,1.1014480428432354`},AxesEdge->{{-1,-1},{1,-1},None},LabelStyle->Directive[Large,FontFamily->"Helvetica"],AxesLabel->{"x","y"}],
Graphics3D[Table[Line[{{0,0,En[n1,n2,L nm,m]/h/(10^9)},{L,0,En[n1,n2,L nm,m]/h/(10^9)},{L,L,En[n1,n2,L nm,m]/h/(10^9)},{0,L,En[n1,n2,L nm,m]/h/(10^9)},{0,0,En[n1,n2,L nm,m]/h/(10^9)}}],{n1,1,nmax},{n2,1,nmax}]],
Graphics3D[Table[Text[Style[(Subscript["E", ToString[n1]<>ToString[n2]]),12,FontFamily->"Helvetica"],{-0.03 (Lmax n2),-0.03 (Lmax n2),En[n1,n2,L nm,m]/h/(10^9)}],{n1,1,nmax},{n2,1,nmax}]]
],{{L,Lmax,"L [nm]"},(10^(-13)),Lmax ,ControlType->Slider,Appearance->"Labeled"},{{n1,1,"(Subscript[n, x])"},1,nmax ,1,ControlType->Slider,Appearance->"Labeled"},{{n2,1,"(Subscript[n, y])"},1,nmax ,1,ControlType->Slider,Appearance->"Labeled"},LabelStyle->Large,SaveDefinitions->True]