  We show that the coupling between a qubit and a single mode cavity can be
estimated from the process tomography data for the qubit alone. All the
parameters of the coupling Hamiltonian between the qubit and the cavity mode
can be obtained from observations on the qubit. We also show that the variance
matrix and the photon number statistics of the single mode cavity can be
reconstructed. Our results provide an alternate means of obtaining the coupling
and reconstructing the state of the cavity mode in comparison with the
techniques presently used.
