  In this paper we analyze the interaction of a uniformly accelerated detector
with a quantum field in (3+1)D spacetime, aiming at the issue of how kinematics
can render vacuum fluctuations the appearance of thermal radiance in the
detector (Unruh effect) and how they engender flux of radiation for observers
afar. Two basic questions are addressed in this study: a) How are vacuum
fluctuations related to the emitted radiation? b) Is there emitted radiation
with energy flux in the Unruh effect? We adopt a method which places the
detector and the field on an equal footing and derive the two-point correlation
functions of the detector and of the field separately with full account of
their interplay. From the exact solutions, we are able to study the complete
process from the initial transient to the final steady state, keeping track of
all activities they engage in and the physical effects manifested. We derive a
quantum radiation formula for a Minkowski observer. We find that there does
exist a positive radiated power of quantum nature emitted by the detector, with
a hint of certain features of the Unruh effect. We further verify that the
total energy of the dressed detector and a part of the radiated energy from the
detector is conserved. However, this part of the radiation ceases in steady
state. So the hint of the Unruh effect in radiated power is actually not
directly from the energy flux that the detector experiences in Unruh effect.
Since all the relevant quantum and statistical information about the detector
(atom) and the field can be obtained from the results presented here, they are
expected to be useful, when appropriately generalized, for addressing issues of
quantum information processing in atomic and optical systems, such as quantum
decoherence, entanglement and teleportation.
