Figure 1

Operation principle. (a) The demon monitors the system (a single-electron transistor) for electrons that tunnel into (panel 1) or out of (panel 3) the island. It then immediately performs a feedback by applying a positive charge to trap (panel 2) or negative charge to repel (panel 4) the electrons. Coulomb blockade ensures that only either one or zero electrons reside in the system island. The electrons are always tunneling against the potential induced by the demon, and therefore the system cools down. (b) Energetics of the system under voltage bias V in the experimental and autonomous realization of the cycle in (a) with another single-electron structure operating as the demon. The conduction electrons of the system follow Fermi distribution, providing electrons that can overcome the energy cost J − e V / 2 , where J is the coupling energy between the system and the demon; however, in doing so, the system cools down by an equal amount. The energy J is dissipated by the demon as it reacts, changing the projected energy cost experienced by the electron tunneling in the system from − J − e V / 2 to J − e V / 2 . Note that here the system island is drawn without Fermi distribution for simplicity. Also, the described operation could, in principle, be performed nonautonomously by externally measuring the system state and changing the energy of the system as feedback; see, e.g., Ref. [25].