  A quantum thermal transistor is designed by the strong coupling between one
qubit and one qutrit which are in contact with three heat baths with different
temperatures. The thermal behavior is analyzed based on the master equation by
both the numerical and the approximately analytic methods. It is shown that the
thermal transistor, as a three-terminal device, allows a weak modulation heat
current (at the modulation terminal) to switch on/off and effectively modulate
the heat current between the other two terminals. In particular, the weak
modulation heat current can induce the strong heat current between the other
two terminals with the multiple-region amplification of heat current.
Furthermore, the heat currents are quite robust to the temperature (current)
fluctuation at the lower-temperature terminal within certain range of
temperature, so it can behave as a heat current stabilizer.
