  Based on homodyne detection, we discuss how the presence of an event horizon
affects quantum communication between an inertial partner, Alice, and a
uniformly accelerated partner, Rob. We show that there exists a low frequency
cutoff for Rob's homodyne detector that maximizes the signal to noise ratio and
it approximately corresponds to the Unruh frequency. In addition, the low
frequency cutoff which minimizes the conditional variance between Alice's input
state and Rob's output state is also approximately equal to the Unruh
frequency. Thus the Unruh frequency provides a natural low frequency cutoff in
order to optimize quantum communication of both classical and quantum
information between Alice and Rob.
