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Light -Atom Interaction - Part 3
Quantization of Electromagnetic Field, Atom-Field System


In this part:
               1.   Algebraic method for harmonic oscillator   -  creation and annihilation  operators   a+  and    a    
                                    this is needed to treat each of the  eigenmodes (  each one is an independent oscillator )

               2.   Quantum theory of the electromagnetic field    -  two expressions for energy of the field
                                    in eigenmodes, using    a+  and    a   and  using the derived operators for electric and magnetic field strengths

               3.   From Lorentz Force to hamiltonian of charged particle in electric - and magnetc - field         ATOM-FIELD INTERACTION

               4.   Applying the golden rule - what will be the matrix elements

                                  

Algebraic method for the Harmonic oscillator - Creation and annihilation of "energy quanta"

        The next three (smaller size  slides)     were shown at the end of       LAST TIME

    the hamiltonian is transformed to simple and symmetric, dimensionless-operator based form
    Linear combination of this dimensionless   coordinate Q  and momentum P      -  leads to annihilation / creation operators

      1220_Harmonic_Oscillator_Creation_Annihilation.png   
                                                                  
       1220_Harmonic_Oscillator_Creation_Annihilation.png


Algebraic method for the Harmonic oscillator - Creation and annihilation of "energy quanta"

               
Linear combination of this dimensionless   coordinate Q  and momentum P      -  leads to annihilation / creation operators
               ONLY USING    commutation relations


      1230_Harmonic_Oscillator_Creation_Annihilation.png
                                                                           
       1230_Harmonic_Oscillator_Creation_Annihilation.png

 
                 Linear combination of this dimensionless   coordinate Q  and momentum P      -  leads to annihilation / creation operators
                 ONLY USING    commutation relations


                Hamiltonian         Number operator         eigenstates characterized   by "number of quanta"


      1250_Harmonic_Oscillator_Creation_Annihilation.png
                                                                          
       1250_Harmonic_Oscillator_Creation_Annihilation.png

                Linear combination of this dimensionless   coordinate Q  and momentum P      -  leads to annihilation / creation operators
               ONLY USING    commutation relations

               creation and annihilation  operators   a+  and    a

              
Hamiltonian         Number operator         eigenstates characterized   by "number of quanta"

      005_creations_commutations.png

       005_creations_commutations.png

 
               Ladder operators      creation and annihilation  operators   a+  and    a

      006_Quanta_Number__LADDER_operator.png

       006_Quanta_Number__LADDER_operator.png


       Looking back at the wavefunction formulation         operators   a+  and    a    are in fact partly differentiation ......
       Schrödinger equation - replaced by effective first order differential equation

      007_differential_eq-via_Ladder_operator.png

       007_differential_eq-via_Ladder_operator.png


Quantum theory of the electromagnetic field   

                              
-  two expressions for energy of the field
                                    in eigenmodes, using    a+  and    a   and  using the derived operators for electric and magnetic field strengths

                                    Establishing the dimensional constant  ( from the equality of the two energies )

      008_Quantum_Description_of Field_vector_pot_A.png

       008_Quantum_Description_of Field_vector_pot_A.png


      Establishing the dimensional constant  ( from the equality of the two energies )

      010_Classical_Quantum_total_energy_same_M.E.png

       010_Classical_Quantum_total_energy_same_M.E.png


       ATOM-FIELD INTERACTION

         From Lorentz Force to hamiltonian of charged particle in electric - and magnetc - field        

      018Charged_Particle_Lorentz_Force.png

       018Charged_Particle_Lorentz_Force.png


       ATOM-FIELD INTERACTION     
                  hamiltonian of charged particle in electric - and magnetc - field        

      019_Field_Atom_Interaction.png

       019_Field_Atom_Interaction.png


       ATOM-FIELD INTERACTION     
                  hamiltonian of charged particle in electric - and magnetc - field    
   
                  a map of the steps in applying Golden Rule            identifying the    H0    and    H1      

      020_Hamilton_Field_Atom_Interaction.png

       020_Hamilton_Field_Atom_Interaction.png


      ATOM-FIELD INTERACTION     
 
                   applying Golden Rule            identifying the    H0    and    H1  initial  and  final (continuum) states        

      030_Apply_Golden_Rule_to_Atom_Field.png

       030_Apply_Golden_Rule_to_Atom_Field.png


     Discussing details of the resulting matrix element     
    
            what are electronic (red) and what are field (blue) components
            the field is quantized, its description is in terms of creation / annihilation expressions

            but the "eigenmodes" are in the normal 3-dim space - so they will be the same as the electron coordinates
                                                                           (   the exp(- i k r ) - r is the same coordinate as the electron )

      060_Matrix_Element.png

       060_Matrix_Element.png



                      Note above the sign in the exponentials  -       ( discussed also in the next lecture )
                      now changed in agreement with literature - but is seemingly opposite to our usual conventions for plane waves

     In the NEXT LECTURE                 we carry through   the details of the light emission rates

                                                            and    discuss the stimulated emission  in this framework


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