  The field of thermotronics aims to develop thermal circuits that operate with
temperature biases and heat currents just as how electronic circuits are based
on voltages and electric currents. Here, we investigate a thermal half-wave
rectifier based on a quantum two-level system (a qubit) that is driven by a
periodically modulated temperature difference across it. To this end, we
present a non-equilibrium Green's function technique, which we extend to the
time domain to account for the time-dependent temperature in one of two thermal
reservoirs connected to the qubit. We find that the qubit acts a thermal diode
in parallel with a thermal capacitor, whose capacitance is controlled by the
coupling to the reservoirs. These findings are important for the efforts to
design non-linear thermal components such as heat rectifiers and multipliers
that operate with more than one diode.
