  Two entangled two-level Unruh-DeWitt detectors, which are in rest,
spontaneously loose entanglement when at least any one of them is not isolated
from the environment quantum fields. For eternal interaction between the
detectors and environment, the spontaneous emission from the detectors' exited
states and vacuum fluctuations of field influence this negative effect.
Consequently, it suggests that two entangled qubits become less communicated
during their free-fall towards the black hole horizon.
