Analysis of multiple exceptional points related to three interacting   eigenmodes in a non-Hermitian Hamiltonian
  We have investigated the exceptional points (EPs) which are degeneracies of a non-Hermitian Hamiltonian, in the case that three modes are interacting with each other. Even though the parametric evolution of the modes cannot be uniquely determined when encircling more than two EPs once, we can recover the initial configuration of the modes by encircling two EPs three times or three EPs twice. We confirm our expectation by numerically calculating the modes of an open quantum system, two dielectric microdisks, and 3$\times$3 matrix model. 
Jung-Wan Ryu, Soo-Young Lee, and Sang Wook Kim
quant-ph