  We investigate bipartite and tripartite entanglement in an open quantum
system, specifically three qubits, all of which are damped, and one of which is
driven. We adapt a systematic approach in calculating the entanglement of
various bipartite splits usinga generalized concurrence as an indicator of
entanglement. Our calculations are based on a direct detection scheme that is a
particular unravelling of the density matrix. This system has a collective
dipole-dipole energy shift that couples the atoms and the dissipation is via
partially collective spontaneous emission described by the Lehmberg-Agarwal
master equation.Our results are unravelling dependent, but apply to
applications of entanglement based on direct detection. We also calculate the
three-way tangle or residual entanglement for this system. We present
calculations for a variety of driving and damping rates, and examine what decay
rate is adequate for the system to be reduced to two qubits with a readout
port. We also consider a specific model of three atoms located at particular
positions in free space.
