Indirect Hamiltonian identification through a small gateway

Identifying the many-body Hamiltonian of a large quantum system is essential in understanding many physical phenomena, yet extremely difficult in general. We show that coupling strengths in networks of spin-1/2 particles can be estimated indirectly through a gateway, provided that the coupling topology is known. The criterion for the feasibility of identification is described only by a simple topological property concerning how the gateway is connected to the entire network. We also address the issues of process efficiency and how degeneracies of the system can be lifted.