  Coherent control of self-contained quantum systems offers the possibility to
fabricate smallest thermal transistors. The steady coherence created by the
delocalization of electronic excited states arouses nonlinear heat transports
in non-equilibrium environment. Applying this result to a three-level quantum
system, we show that quantum coherence gives rise to negative differential
thermal resistances, making the thermal transistor suitable for thermal
amplification. The results show that quantum coherence facilitates efficient
thermal signal processing and can open a new field in the application of
quantum thermal management devices.
