  Identifying the nature of interactions in a quantum system is essential in
understanding any physical phenomena. Acquiring information on the Hamiltonian
can be a tough challenge in many-body systems because it generally requires
access to all parts of the system. We show that if the coupling topology is
known, the Hamiltonian identification is indeed possible indirectly even though
only a small gateway to the system is used. Surprisingly, even a degenerate
Hamiltonian can be estimated by applying an extra field to the gateway.
