  Optical Bloch Equations (OBE) model the dynamics of a classically driven
two-level atom coupled to a thermal electromagnetic field. From a global
viewpoint, they derive from the unitary evolution of a closed, isolated
atom-field system. We study the emergence of the OBE in the case where the
driving and the thermal fields are confined in one spatial dimension -- a
situation usually found in waveguide-QED. The joint atom-field system forms a
"one-dimensional atom" (1D atom) whose closed dynamics can be solved, providing
access to light-matter correlations. Such closure of the OBE unveils a new term
capturing the driving of the atom by itself, or self-drive, which is
proportional to the atom coherences in the energy basis. A 1D atom also
constitutes an autonomous, energy-conserving system. Hence, energy exchanges
between the atom and the field can be conveniently analyzed as closed first
laws, where work-like (heat-like) flows stem from effective unitaries
(correlations) exerted by one system on the other. We show that the closed and
the open approaches only differ by the atom self-work, which yields a tighter
expression of the second law. We quantitatively relate this tightening to the
extra-knowledge acquired by closing the OBE. The concepts and effects we
introduce deepen our understanding of thermodynamics in the quantum regime and
its potential for energy management at quantum scales. They can be probed in
state-of-the-art quantum hardware, e.g. superconducting and photonic circuits.
