Fig. 3

Heat engines and chillers. a The cycle for a quantum-dot chiller. The solid curve in the temperature-entropy plot shows these quantities for the quantum-dot as it is driven by a laser pulse and absorbs heat from the phonon bath. The temperature shown is defined by Eq. (4). The wavy lines depict the subsequent radiative decay, which returns the quantum dot to its ground state. The upper (lower) square box in the engine diagram represents the phonon (electromagnetic) environment, and the circle the quantum dot. b The cycle for a quantum-dot heat engine. This comprises the same heat-absorption stroke as the chiller, but the cycle is then closed by a partial Carnot cycle, which implements a reversible heat transfer to a bath at a temperature T_c < T_ph