  We investigate the quantum discord dynamics and inversion operator of a
two-level atom initially in thermal equilibrium mixed state interacting with a
cavity field prepared in a n-photon Fock state. We considered the
Jaynes-Cummings model which is an exactly quantum mechanical model of
interaction between two different quantum systems, an optical cavity in single
mode n-photon Fock state and a two-level atom. The influence of interaction
time and measurement basis used for calculating the conditional entropy is
discussed on the evolution of the quantum discord and on its minimum. The
evolution of mean value of inversion operator with interaction is also
discussed. It is found that the quantum discord and inversion both shows
oscillatory behaviour and also shows the phenomenon of beats with interaction
time. For a given initial cavity photon Fock state the beat period of minimum
quantum discord is one half of that for inversion operator. However, as the
number of photons in cavity increases the frequency of oscillations of quantum
discord and inversion increases.
