Real-time dynamics without Hamiltonians

We set up a real-time (Schwinger-Keldysh) path integral to study the evolution of quantum systems driven in real-time completely through the coupling of the system with the environment. This can also be interpreted as measurements being performed on the system, but without being driven by a Hamiltonian. The initial state, is however, prepared with a particular Hamiltonian. While the sign-problem associated with the "real-time" is absent, the measurement process can generate it's own sign-problem.  For a spin-1/2 system, in particular, when the measurement results are averaged over, the resulting sign problem completely disappears, and the system can be simulated with an efficient cluster algorithm. We will also outline the possible extension of this approach to fermionic systems dissipatively coupled to their environment.