  We investigate the Quantum Zeno Effect in spin 1/2, spin 1 and spin 3/2 open
quantum systems undergoing Rabi oscillations, revealing unexplored features for
the spin 1 and spin 3/2 systems. The systems interact with an environment
designed to perform continuous measurements of an observable, driving the
systems stochastically towards one of the eigenstates of the corresponding
operator. The system-environment coupling constant represents the strength of
the measurement. Stochastic quantum trajectories are generated by unravelling a
Markovian Lindblad master equation using the quantum state diffusion formalism.
These are regarded as a more appropriate representation of system behaviour
than consideration of the averaged evolution since the latter can mask the
effect of measurement. Complete positivity is maintained and thus the
trajectories can be considered as physically meaningful. The Quantum Zeno
Effect is investigated over a range of measurement strengths. Increasing the
strength leads to greater system dwell in the vicinity of the eigenstates of
the measured observable and lengthens the time taken by the system to return to
that eigenstate,thus the Quantum Zeno Effect emerges. For very strong
measurement, the Rabi oscillations resemble randomly occurring
near-instantaneous jumps between eigenstates. The trajectories followed by the
quantum system are heavily dependent on the measurement strength which other
than slowing down and adding noise to the Rabi oscillations, changes the paths
taken in spin phase space from a circular precession into elaborate
figures-of-eight. For spin 1 and spin 3/2 systems, the measurement strength
determines which eigenstates are explored and the Quantum Zeno Effect is
stronger when the system dwells in the vicinity of certain eigenstates compared
to others.
