A system of two coupled oscillators has two natural frequencies. As the coupling strength between the oscillators increases, the lower frequency decreases and the higher increases. This effect can be viewed as a 'repulsion' between the frequencies. The quantum mechanical equivalent to this repulsion effect as known as level repulsion or the Wigner–von Neumann anticrossing rule.

See also

• Intersubband polariton
• Wigner–Ville distribution
• Avoided crossing
  Avoided crossing
  [Image:Avoided_crossing.png|thumb|right|300px|An avoided energy level crossing in a two level system subjected to an external magnetic field. Note the energies of the diabatic states, \scriptstyle...