RQC Seminar

248th RQC Seminar

• Speaker

  Prof. Kay Brandner
  ( University of Nottingham, UK )

• Date

  16:00-17:00, (4:00p.m.-5:00p.m.) Monday, December 15, 2025

• Venue

  Hybrid( Zoom,
  Seminar Room 345-347, 3F, Main Research Building, Wako Campus / 研究本館3階 セミナー室 (345-347) (C01))

• Title

  Thermodynamic Uncertainty Relations for Coherent Transport

• Inquiries

  norilab_rqc_assist[at]ml.riken.jp

Abstract
Thermodynamic uncertainty relations (TURs) describe a trade-off between precision and dissipation in nonequilibrium thermodynamic processes. Specifically, they provide universal lower bounds on the overall rate of entropy production that depend only on the mean value and fluctuations of a single current. Beyond their conceptual significance, TURs enable the inference of bounds on physical quantities that are difficult to measure directly, such as the efficiency of molecular motors or other types of mesoscopic machines.

Coherent conductors offer a versatile platform for exploring the impact of quantum effects on the precision–dissipation trade-off. These systems can be described within a simple and transparent theoretical framework based on the Landauer–Büttiker model of noninteracting transport carriers. At the same time, they can be experimentally realized with a high degree of accuracy using nanoscale structures at millikelvin temperatures, molecular junctions or ultracold atoms in tailored trapping potentials.

In this talk, we consider general multi-terminal coherent conductors. As a reference, we first derive a TUR that holds under the assumption that transport carriers behave as classical particles, but breaks down in the quantum regime due to the Pauli exclusion principle. We then derive a generalized TUR that accounts for this effect solely by changing the relative weight of fluctuations and dissipation. This bound holds for any multi-terminal geometry and scattering potential, and arbitrarily far from equilibrium. It can be saturated in two-terminal setups with a narrow, boxcar-shaped transmission function and, like its classical counterpart, can be used to establish physically transparent trade-off relations between the figures of merit of small-scale thermal machines such as thermoelectric heat engines and refrigerators. Finally, we show that, at least in time-reversal-symmetric settings, our generalized TUR for coherent transport follows from a more general thermodynamic constraint on the large-deviation functions of particle currents, which bounds both typical and rare fluctuations.