Collapse and revival and cat states with anN-spin system

We discuss collapse and revival of Rabi oscillations in a system comprising a qubit and a ``big spin'' (made of N qubits, or spin-$1/2$ particles). We demonstrate a regime of behavior analogous to conventional collapse and revival for a qubit-field system, employing spin coherent states for the initial state of the big spin. These dynamics can be used to create a cat state of the big spin. Even for relatively small values of N, states with significant potential for quantum metrology applications can result, giving sensitivity approaching the Heisenberg limit.