  Entanglement degradation appears to be a generic prediction in relativistic
quantum information whenever horizons restrict access to a region of spacetime.
This property has been previously explored in connection with the Unruh effect,
where a bipartite entangled system composed of an inertial observer (Alice) and
a uniformly accelerated observer (Rob) was studied, with entanglement
degradation caused by the relative acceleration -- and with equivalent results
for the case when Alice is freely falling into a black hole and Rob experiences
a constant proper acceleration as a stationary near-horizon observer. In this
work, we show that a similar degradation also occurs in the case of an
entangled system composed of an inertial observer (Alice) and a "diamond
observer" (Dave) with a finite lifetime. The condition of a finite lifetime is
equivalent to the restriction of Dave's access within a causal diamond.
Specifically, if the system starts in a maximally entangled state, prepared
from Alice's perspective, entanglement degradation is enforced by the presence
of the diamond's causal horizons.
