  Imagine that you have several sets of two coupled qubits, but you do not know
the parameters of their Hamitonians. How to determine these without resorting
to the usual spectroscopy approach to the problem? Based on numerical modeling,
we show that all the parameters of a system of two coupled qubits can be
determined by applying to it an external classical noise and analysing the
Fourier spectrum of the elements of the system's density matrix. In particular,
the interlevel spacings as well as the strength and sign of qubit-qubit
coupling can be determined this way.

Quantum Physics