  We reveal the potentially important role of a general mechanism that has
hitherto not been invoked in quantum heat management schemes, namely, spectral
filtering of the coupling between the heat baths in the setup and the quantum
system that controls the heat flow. Such filtering is enabled by interfaces
between the system and the baths by means of harmonic-oscillator modes whose
resonant frequencies and coupling strengths are used as control parameters of
the system-bath coupling spectra. We show that this uniquely
quantum-electrodynamic mechanism, here dubbed bath spectral filtering, boosts
the performance of a minimal quantum heat manager comprised of two interacting
qubits or an analogous optomechanical system, allowing this device to attain
either perfect heat diode action or strongly enhanced heat transistor action.
