  It is problematic to interpret the quantum jumps of an atom interacting with
thermal light in terms of counts at detectors monitoring the atom's inputs and
outputs. As an alternative, we develop an interpretation based on a
self-consistency argument. We include one mode of the thermal field in the
system Hamiltonian and describe its interaction with the atom by an entangled
quantum state while assuming that the other modes induce quantum jumps in the
usual fashion. In the weak-coupling limit, the photon number expectation of the
selected mode is also seen to execute quantum jumps, although more generally,
for stronger coupling, Rabi oscillations are observed; the equilibrium photon
number distribution is a Bose-Einstein distribution. Each mode may be viewed in
isolation in a similar fashion, and summing over their weak-coupling jump rates
returns the net jump rates for the atom assumed at the outset.

Quantum Physics