Special CPM Seminar/Quantum Lunch

Time-dependent single-electron transport: irreversibility and out-of-equilibrium properties

Klaus Ensslin

ETH Zürich

The second law of thermodynamics states that a macroscopic system out of thermal equilibrium will irreversibly move toward equilibrium driven by a steady increase of its entropy. This macroscopic irreversibility occurs despite the time-reversal symmetry of the underlying microscopic equations of motion. Also, a microscopic system will undergo an irreversible evolution on a long time scale, but, over a sufficiently short observation time both entropy-producing trajectories as well as their time-reversed entropy-consuming counterparts occur. It is only because of the statistics of these occurrences that a long-term irreversible evolution is established. This phenomenon is described by the fluctuation theorem. As a step toward the direct test of the fluctuation theorem in the quantum regime, we verify the fluctuation theorem in single- electron tunneling at low temperatures, although our experiment is carried out in the regime of classical charge counting. We employ real-time detection of single-electron charging in quantum dots (QDs). Monitoring the charge state of two QDs that are coupled both in series and to source and drain electrodes allows us to measure the direction-resolved charge flow through this device and consequently the current probability distribution. In order to avoid the spurious backaction, we employ an optimized sample design that combines electron-beam and scanning-probe lithography. It provides the high tunability and electronic stability required for the experiment while maintaining a good QPC-DQD coupling.