We propose a method for the direct extraction of the complex hadron-hadron optical potential (or, equivalently, the phase shift and inelaticity in a given channel) on the lattice, which does not require the use of the multi-channel Luscher formalism, but the knowledge of a tower of energy levels only.
The approach works for any multi-particle states and tested explicitely on a set of synthetic data for the pi eta/Kbar K system. Further, we show how a sufficiently large number of energy eigenvalues can be obtained utilizing partial twisting.