  The two-hole excitation spectrum of the t-J ladder at half-filling is studied
using linked-cluster series expansion methods. A rich spectrum of bound states
emerges, particularly at small $t/J$. Their dispersion relations and coherence
lengths are computed, along with the threshold behaviour as the bound states
merge into the continuum. A class of 4-hole bound states is also studied,
leading to the conclusion that phase separation occurs for $t/J \lesssim 0.5$,
in agreement with other studies.
