Janine Splettstößer
(Chalmers University of Technology, Sweden)

Abstract:
In small-scale thermodynamic devices, fluctuations play an important role (in contrast to standard classical thermodynamics). While close to equilibrium fluctuation-dissipation theorems prescribe how the fluctuations are connected to the desired average output of a device, this is much more difficult to identify far from equilibrium.
Interestingly, the thermodynamic properties of a process or of a system constrain fluctuations. This has been studied in terms of thermodynamic and kinetic uncertainty relation (TURs and KURs) - in particular in weakly coupled open quantum systems. However, steady-state thermoelectric heat engines operate typically far from equilibrium and the coupling to contacts can be strong.
In this presentation, I will show our recent results on thermodynamic and kinetic constraints on fluctuations. I will focus on implications for quantum heat engines, namely quantum systems subject to temperature differences which can be exploited for power production at small scales.
I will  start by introducing fluctuation-dissipation bounds, which constrain the charge-current fluctuations by the dissipated power, both in steady-state ^[1], as well as in time-dependently driven systems ^[2]. In contrast to the well-known fluctuation-dissipation theorem, these bounds are particularly predictive for large temperature bias.
Furthermore, I will show that KUR-like constraintss can be derived from scattering theory, where the “activity”,  is replaced by activity-like transport quantities like particle-current noise and transport bandwidth ^[3,4].
While these constraints are limited to systems described by linear Hamiltonians, we have recently developed a quantum KUR via the Cramér-Rao bound, where the quantum Fisher information takes the role of a partial dynamical activity bounding precision together with a susceptibility term in response to changes in the system-bath coupling strength ^[5].
 
^[1] L. Tesser, J. Splettstoesser: Out-of-Equilibrium Fluctuation-Dissipation Bounds. Phys. Rev. Lett. 132, 186304 (2024)
^[2] L. Tesser, J. Balduque, J. Splettstoesser: Fluctuation-dissipation bounds for time-dependently driven conductors. arXiv:2509.07583 (2025)
^[3] D. Palmqvist, L. Tesser, J. Splettstoesser: Kinetic Uncertainty Relations for Quantum Transport. Phys. Rev. Lett. 135, 166302 (2025)
^[4] D. Palmqvist, L. Tesser, J. Splettstoesser: Combining kinetic and thermodynamic uncertainty relations in quantum transport. Quantum Sci. Technol. 10, 035059 (2025)
^[5] D. Palmqvist, L. Tesser, J. Splettstoesser: Susceptibility-kinetic uncertainty relations for quantum systems. arXiv:2607.01035 (2026)
 

Zoom registration link:
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