sentences:  The dynamics of the electromagnetic field of the monochromatic laser can be derived by first treating the two-level atom as a spin-1/2 system with two energy eigenstates which have energy separation of ħω.The dynamics of the atom can then be described by the three rotation operators, formula_1,formula_2,formula_3, acting upon the Bloch sphere.Thus the energy of the system is described entirely through an electric dipole interaction between the atom and field with the resulting hamiltonian being described by
  
  formula_4 .