Instantonic approach to triple well potential
  By using a usual instanton method we obtain the energy splitting due to quantum tunneling through the triple well barrier. It is shown that the term related to the midpoint of the energy splitting in propagator is quite different from that of double well case, in that it is proportional to the algebraic average of the frequencies of the left and central wells. 
Soo-Young Lee, Jae-Rok Kahng, Sahng-Kyoon Yoo, D.K.Park, C.H.Lee,   Chang Soo Park, Eui-Soon Yim