Heat transport, fluctuations, and Maxwell's demon in electronic nanocircuits

The field of thermodynamics describes the properties of a system that is coupled to one or several heat baths. A new direction in the field is to investigate the thermodynamics at microscopic level, considering the stochastic evolution of individual system state trajectories. A thought experiment presented over 150 years ago, which is known as Maxwell's demon and apparently violates the Second law of thermodynamics, is currently investigated to assess the relation between information and energy. This thesis studies stochastic thermodynamics and Maxwell's demon experimentally in electronic nanocircuits. The first part of the thesis covers the basic thermodynamic concepts and recently discovered fluctuation relations. The original thought experiments of Maxwell's demon and Szilard's engine are presented, after which information in thermodynamics is discussed in more detail. Next, this thesis discusses heat transport in metallic nanoelectronic circuits. A superconductor, which ideally is an excellent thermal insulator, leaks heat in a direct contact to a normal metal due to a phenomenon known as inverse proximity effect. This thesis describes the measurement of this heat leak, and demonstrates how inverse proximity effect can be exploited to fabricate fully normal aluminum-based tunnel junctions. The remaining part of the thesis is about devices based on single-electron phenomena, and the experiments on stochastic thermodynamics presented here are based on them. An experimental setup based on a device known as a single-electron box is used to determine distributions of thermodynamic quantities, by which the fluctuation relations are tested experimental-ly in the case of multiple heat baths, and by which the general properties of the distribution are investigated as a function of temperature. Moreover, the setup is operated as a Szilard's engine, where one bit of information is used to extract energy equal to k_BT ln(2), where k_B is the Boltzmann constant and T is the temperature.Finally, heat transfer in single-electron devices is investigated at the level where the effect of heat generation is measurable as a change in temperature. The thesis shows how a device known as a single electron transistor can be operated to achieve local cooling. Furthermore, when such a device is coupled to a similar one, the setup realizes an autonomous Maxwell's demon. The presented experiment shows how the whole transistor cools down, however the coupled device (the demon) heats up corresponding to the information flow between them.