  The Dynamical Mean Field Theory (DMFT) is a powerful tool for calculating
highly correlated systems (both bosonic and fermionic) in a state of
thermodynamic equilibrium. However, in the case of non-equilibrium states, the
method has significant limitations that do not allow obtaining correct results.
The stumbling block here is the impurity solver: a method for calculating the
dynamics of an open system. In this work we present the prototype of a
universal impurity solver for the DMFT method which can solve both equilibrium
and non-equilibrium problems. We analyse spectral functions of Bose-Hubbard
model on the Bethe lattice in different regimes and show that our solver gives
correct and physical results.
